HK1193283A - Motion vector determination for video coding - Google Patents

Description

Motion vector determination for video coding

This application claims the rights of united states provisional application No. 61/535,964, filed on 9/17/2011, united states provisional application No. 61/564,764, filed on 11/29/2011, and united states provisional application No. 61/564,799, filed on 11/29/2011, each of which is incorporated herein by reference in its entirety.

Technical Field

This disclosure relates to video coding, and more particularly, to inter-prediction of video data.

Background

Digital video capabilities can be incorporated into a wide variety of devices, including digital televisions, digital direct broadcast systems, wireless broadcast systems, Personal Digital Assistants (PDAs), laptop or desktop computers, digital cameras, digital recording devices, digital media players, video gaming devices, video gaming consoles, cellular or satellite radio telephones, video teleconferencing devices, and the like. Digital video devices implement video compression techniques, such as the standards defined by MPEG-2, MPEG-4, ITU-T h.263, ITU-T h.264/MPEG-4 part 10 (advanced video coding (AVC)), the High Efficiency Video Coding (HEVC) standard currently under development, and the video compression techniques described in the extensions of the standards, to more efficiently transmit, receive, and store digital video information.

Video compression techniques perform spatial (intra picture) prediction and/or temporal (inter picture) prediction to reduce or remove redundancy inherent in video sequences. For block-based video coding, a video slice may be partitioned into video blocks, which may also be referred to as treeblocks, Coding Units (CUs), and/or coding nodes. Video blocks in an intra-coded (I) slice of a picture are encoded using spatial prediction with respect to reference samples in neighboring blocks in the same picture. Video blocks in an inter-coded (P or B) slice of a picture may use spatial prediction with respect to reference samples in neighboring blocks in the same picture or use temporal prediction with respect to reference samples in other reference pictures. A picture may be referred to as a frame and a reference picture may be referred to as a reference frame.

Disclosure of Invention

In general, techniques are described for encoding and decoding video data. The video coder generates a candidate list for each Prediction Unit (PU) of the current Coding Unit (CU) according to a merge mode or an Advanced Motion Vector Prediction (AMVP) process. The video coder generates the candidate list such that each candidate in the candidate list generated based on motion information of at least one other PU is generated without using motion information of any other PU that belongs to the current CU. The candidates generated based on the motion information of the other PUs may include original candidates that indicate motion information of the other PUs and candidates that indicate motion information derived from motion information of one or more other PUs. After generating the candidate list for a PU, the video coder may generate a predictive video block for the PU based on one or more reference blocks indicated by motion information of the PU. The motion information of the PU may be determined based on motion vectors indicated by one or more selected candidates in the candidate list for the PU. Because the candidates in the candidate list for the PU of the current CU are not generated using motion information of any other PUs of the current CU, the video coder may generate the candidate lists for one or more of the PUs of the current CU in parallel.

This disclosure describes a method for coding video data. The method comprises the following steps: for each PU of a plurality of PUs belonging to a current CU, generating a candidate list for the PU such that each candidate in the candidate list generated based on motion information of at least one other PU is generated without using motion information of any other PU belonging to the current CU. In addition, the method comprises: for each PU belonging to the current CU, generating a predictive video block for the PU based on a reference block indicated by motion information of the PU, the motion information of the PU being determinable based on a motion vector indicated by a selected candidate in the candidate list for the PU.

Additionally, this disclosure describes a video coding device comprising one or more processors configured to: for each PU of a plurality of PUs belonging to a current CU, generating a candidate list for the PU such that each candidate in the candidate list generated based on motion information of at least one other PU is generated without using motion information of any of the PUs belonging to the current CU. The one or more processors are further configured to: for each PU belonging to the current CU, generating a predictive video block for the PU based on a reference block indicated by motion information of the PU, the motion information of the PU being determinable based on a motion vector indicated by a selected candidate in the candidate list for the PU.

In addition, this disclosure describes a video coding device comprising means for, for each PU of a plurality of PUs belonging to a current CU, generating a candidate list for the PU such that each candidate in the candidate list generated based on motion information of at least one other PU is generated without using motion information of any of the PUs belonging to the current CU. In addition, the video coding device comprises means for generating, for each PU belonging to the current CU, a predictive video block for the PU based on a reference block indicated by motion information of the PU, the motion information of the PU being determinable based on a motion vector indicated by a selected candidate in the candidate list for the PU.

Additionally, this disclosure describes a computer program product comprising one or more computer-readable storage media storing instructions that, when executed, configure one or more processors to: for each PU of a plurality of PUs belonging to a current CU, generating a candidate list for the PU such that each candidate in the candidate list generated based on motion information of at least one other PU is generated without using motion information of any of the PUs belonging to the current CU. The instructions also configure the one or more processors to: for each PU belonging to the current CU, generating a predictive video block for the PU based on a reference block indicated by motion information of the PU, the motion information of the PU being determinable based on a motion vector indicated by a selected candidate in the candidate list for the PU.

The details of one or more examples are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.

Drawings

FIG. 1 is a block diagram illustrating an example video coding system that may utilize techniques of this disclosure.

FIG. 2 is a block diagram illustrating an example video encoder that may be configured to implement the techniques of this disclosure.

FIG. 3 is a block diagram illustrating an example video decoder that may be configured to implement the techniques of this disclosure.

Fig. 4 is a block diagram illustrating an example configuration of an inter prediction module.

FIG. 5 is a flow diagram illustrating an example merge operation.

Fig. 6 is a flow diagram illustrating an example Advanced Motion Vector Prediction (AMVP) operation.

Fig. 7 is a flow diagram illustrating an example motion compensation operation performed by a video decoder.

Fig. 8A is a conceptual diagram illustrating a Coding Unit (CU) and an example source location associated with the CU.

FIG. 8B is a conceptual diagram illustrating a CU and an example alternative source location associated with the CU.

Fig. 9A is a conceptual diagram illustrating an example reference index source location to the left of a 2NxN partitioned CU.

Fig. 9B is a conceptual diagram illustrating an example reference index source location to the left of an Nx 2N-partitioned CU.

Fig. 9C is a conceptual diagram illustrating an example reference index source location above a 2NxN partitioned CU.

Fig. 9D is a conceptual diagram illustrating an example reference index source location above an Nx 2N-partitioned CU.

Fig. 9E is a conceptual diagram illustrating an example reference index source location to the left of an NxN partitioned CU.

Fig. 9F is a conceptual diagram illustrating an example reference index source location above an NxN partitioned CU.

Fig. 10A is a conceptual diagram illustrating an example reference index source location to the left of a 2NxN partitioned CU.

Fig. 10B is a conceptual diagram illustrating an example reference index source location to the left of an Nx 2N-partitioned CU.

Fig. 10C is a conceptual diagram illustrating an example reference index source location above a 2NxN partitioned CU.

Fig. 10D is a conceptual diagram illustrating an example reference index source location above an Nx 2N-partitioned CU.

Fig. 10E is a conceptual diagram illustrating an example reference index source location to the left of an NxN-partitioned CU.

FIG. 11 is a flow diagram illustrating example operations to generate time candidates for a PU.

FIG. 12 is a flowchart illustrating a first example operation to generate a candidate list for a PU.

FIG. 13 is a flow diagram illustrating a second example operation to generate a candidate list for a PU.

Fig. 14A is a conceptual diagram illustrating example spatial candidate source locations associated with a left PU of an example Nx 2N-partitioned CU.

Fig. 14B is a conceptual diagram illustrating example spatial candidate source locations associated with a lower PU of a 2NxN partitioned CU.

Fig. 15A-15D are conceptual diagrams illustrating example spatial candidate source locations associated with PUs of an NxN partitioned CU.

Detailed Description

A video encoder may perform inter prediction to reduce temporal redundancy between pictures. As described below, a Coding Unit (CU) may have multiple Prediction Units (PUs). In other words, multiple PUs may belong to a CU. When the video encoder performs inter prediction, the video encoder may signal motion information for the PU. The motion information of the PU may include a reference picture index, a motion vector, and a prediction direction indicator. The motion vector may indicate a displacement between a video block of the PU and a reference block of the PU. The reference block of the PU may be part of a reference picture that is similar to the video block of the PU. The reference block may be in a reference picture indicated by a reference picture index and a prediction direction indicator.

To reduce the number of bits needed to represent the motion information of the PU, the video encoder may generate a candidate list for each of the PUs according to a merge mode or Advanced Motion Vector Prediction (AMVP) process. Each candidate in the candidate list for the PU may indicate motion information. The motion information indicated by some of the candidates in the candidate list may be based on the motion information of other PUs. For example, the candidate list may include "original" candidates that indicate motion information for PUs that encompass a specified spatial or temporal candidate location. Furthermore, in some examples, the candidate list may include candidates generated by combining partial motion vectors from different original candidates. Furthermore, the candidate list may include "artificial" candidates that are not generated based on the motion information of other PUs, such as candidates that indicate motion vectors with zero magnitude.

According to the techniques of this disclosure, a video encoder may generate a candidate list for each PU of a CU such that each candidate in the candidate list generated based on motion information of at least one other PU is generated without using motion information of any other PU belonging to the CU. Because the candidates in the candidate list are not generated using motion information of any other PU of the same CU, the video encoder may be able to generate the candidate lists in parallel. Generating the candidate lists in parallel may facilitate implementation of a video encoder. In some cases, generating the candidate lists in parallel may be faster than generating the candidate lists continuously.

After generating the candidate list for the PU of the CU, the video encoder may select a candidate from the candidate list and output the candidate index in the bitstream. The candidate index may indicate a position of the selected candidate in the candidate list. The video encoder may also generate a predictive video block for the PU based on the reference block indicated by the motion information of the PU. The motion information of the PU may be determined based on the motion information indicated by the selected candidate. For example, in merge mode, the motion information of the PU may be the same as the motion information indicated by the selected candidate. In AMVP mode, the motion information for the PU may be determined based on the motion vector difference for the PU and the motion information indicated by the selected candidate. The video encoder may generate one or more residual video blocks for the CU based on the prediction video blocks of the PUs of the CU and the original video blocks for the CU. The video encoder may then encode and output one or more residual video blocks in the bitstream.

The video decoder may generate a candidate list for each of the PUs of the CU. In accordance with the techniques of this disclosure, a video decoder may generate a candidate list for a PU for each of the PUs such that each candidate in the candidate list generated based on motion information of at least one other PU is generated without using motion information of any other PU belonging to the CU. The candidate list generated by the video decoder for the PU may be the same as the candidate list generated by the video encoder for the PU. Because the video decoder may generate each of the candidates in the candidate list without using motion information of any other PU of the CU, the video decoder may be able to generate the candidate lists in parallel.

The bitstream may include data identifying a selected candidate in the candidate list of PUs. The video decoder may determine the motion information of the PU based on the motion information indicated by the selected candidate in the candidate list of the PU. The video decoder may identify one or more reference blocks for the PU based on the motion information of the PU. After identifying the one or more reference blocks of the PU, the video decoder may generate a predictive video block for the PU based on the one or more reference blocks of the PU. The video decoder may reconstruct the video blocks for the CU based on the predictive video blocks for the PUs of the CU and the one or more residual video blocks for the CU.

Thus, the techniques of this disclosure may enable a video coder (i.e., a video encoder or a video decoder) to: for each PU of a plurality of PUs belonging to a current CU, generating a candidate list for the PU such that each candidate in the candidate list generated based on motion information of at least one other PU is generated without using motion information of any other PU belonging to the current CU. The video coder may, for each PU belonging to the current CU, generate a predictive video block for the PU based on a reference block indicated by motion information of the PU, the motion information of the PU being determinable based on a motion vector indicated by a selected candidate in the candidate list for the PU.

For ease of explanation, this disclosure may describe locations or video blocks as having various spatial relationships with CUs or PUs. This description may be interpreted to mean that the locations or video blocks have various spatial relationships to the video blocks associated with the CUs or PUs. Furthermore, this disclosure may refer to a PU that the video coder is currently coding as the current PU. This disclosure may refer to a CU that a video coder is currently coding as the current CU. This disclosure may refer to the picture that the video coder is currently coding as the current picture.

The figures illustrate several examples. Elements indicated by reference numerals in the drawings correspond to elements indicated by similar reference numerals in the following description. In the present disclosure, elements having names beginning with ordinal words (e.g., "first," "second," "third," etc.) do not necessarily imply a particular order to the elements. Rather, such ordinal words are used only to refer to different elements of the same or similar type.

FIG. 1 is a block diagram illustrating an example video coding system 10 that may utilize techniques of this disclosure. As used in the description herein, the term "video coder" generally refers to both video encoders and video decoders. In this disclosure, the terms "video coding" or "coding" may generally refer to video encoding and video decoding.

As shown in fig. 1, video coding system 10 includes a source device 12 and a destination device 14. Source device 12 generates encoded video data. Accordingly, source device 12 may be referred to as a video encoding device. Destination device 14 may decode the encoded video data generated by source device 12. Destination device 14 may therefore be referred to as a video decoding device. Source device 12 and destination device 14 may be examples of video coding devices.

Source device 12 and destination device 14 may comprise a wide variety of devices, including desktop computers, mobile computing devices, notebook (e.g., laptop) computers, tablet computers, set-top boxes, telephone handsets (e.g., so-called "smart" phones), televisions, cameras, display devices, digital media players, video game consoles, in-vehicle computers, and the like. In some examples, source device 12 and destination device 14 may be equipped for wireless communication.

Destination device 14 may receive encoded video data from source device 12 via channel 16. Channel 16 may comprise a type of media or device capable of moving encoded video data from source device 12 to destination device 14. In one example, channel 16 may comprise a communication medium that enables source device 12 to transmit encoded video data directly to destination device 14 in real-time. In this example, source device 12 may modulate the encoded video data according to a communication standard (e.g., a wireless communication protocol), and may transmit the modulated video data to destination device 14. The communication medium may comprise a wireless or wired communication medium such as a Radio Frequency (RF) spectrum or one or more physical transmission lines. The communication medium may form part of a packet-based network, such as a local area network, a wide area network, or a global network such as the internet. The communication medium may include a router, switch, base station, or other apparatus that facilitates communication from source device 12 to destination device 14.

In another example, channel 16 may correspond to a storage medium that stores encoded video data generated by source device 12. In this example, destination device 14 may access the storage medium via disk access or card access. The storage medium may comprise a variety of locally-accessible data storage media such as blu-ray discs, DVDs, CD-ROMs, flash memory, or other suitable digital storage media for storing encoded video data. In another example, channel 16 may include a file server or another intermediate storage device that stores encoded video generated by source device 12. In this example, destination device 14 may access the encoded video data stored at a file server or other intermediate storage device via streaming or download. The file server may be a server of the type capable of storing encoded video data and transmitting the encoded video data to destination device 14. Example file servers include web servers (e.g., for a website), File Transfer Protocol (FTP) servers, Network Attached Storage (NAS) devices, and local disk drives. Destination device 14 may access the encoded video data over a standard data connection, including an internet connection. Example types of data connections may include a wireless channel (e.g., a Wi-Fi connection), a wired connection (e.g., DSL, cable modem, etc.), or a combination of both, suitable for accessing encoded video data stored on a file server. The transmission of the encoded video data from the file server may be a streaming transmission, a download transmission, or a combination of both.

The techniques of this disclosure are not limited to wireless applications or settings. The techniques may be applied to video coding in support of any of a variety of multimedia applications, such as: over-the-air television broadcasts, cable television transmissions, satellite television transmissions, streaming video transmissions (e.g., via the internet), encoding digital video for storage on a data storage medium, decoding digital video stored on a data storage medium, or other applications. In some examples, video coding system 10 may be configured to support one-way or two-way video transmission to support applications such as video streaming, video playback, video broadcasting, and/or video telephony.

In the example of fig. 1, source device 12 includes a video source 18, a video encoder 20, and an output interface 22. In some cases, output interface 22 may include a modulator/demodulator (modem) and/or a transmitter. In source device 12, video source 18 may comprise a source, such as a video capture device (e.g., a video camera), a video archive containing previously captured video data, a video feed interface to receive video data from a video content provider, and/or a computer graphics system for generating video data, or a combination of such sources.

Video encoder 20 may encode captured, pre-captured, or computer-generated video data. The encoded video data may be transmitted directly to destination device 14 via output interface 22 of source device 12. The encoded video data may also be stored on a storage medium or file server for later access by destination device 14 for decoding and/or playback.

In the example of fig. 1, destination device 14 includes an input interface 28, a video decoder 30, and a display device 32. In some cases, input interface 28 may include a receiver and/or a modem. Input interface 28 of destination device 14 receives the encoded video data over channel 16. The encoded video data may include a variety of syntax elements generated by video encoder 20 that represent the video data. Such syntax elements may be included within encoded video data transmitted on a communication medium, stored on a storage medium, or stored in a file server.

The display device 32 may be integrated with the destination device 14 or may be external to the destination device 14. In some examples, destination device 14 may include an integrated display device and may also be configured to interface with an external display device. In other examples, destination device 14 may be a display device. In general, display device 32 displays the decoded video data to a user. The display device 32 may comprise any of a variety of display devices, such as a Liquid Crystal Display (LCD), a plasma display, an Organic Light Emitting Diode (OLED) display, or another type of display device.

Video encoder 20 and video decoder 30 may operate according to a video compression standard, such as the High Efficiency Video Coding (HEVC) standard currently under development, and may conform to the HEVC test model (HM). A recent draft of the upcoming HEVC standard, referred to as "HEVC working draft 7" or "WD 7", is described in Bross et al, document JCTVC-I1003_ d54, "High Efficiency Video Coding (HEVC) text Specification draft 7" (JCT-VC, Joint collaborative team of video coding (JCT-VC) of ITU-T SG16WP3 and ISO/IECJTC1/SC29/WG11, conference 9: Switzerland, Indoway, 5 months 2012), which is downloadable from http:// phenix. int-evry. fr/ict/doc _ end _ user/documents/9_ Geneva/wgl1/JCTVC-I1003-v6.zip from 19 days 2012, the entire contents of which are incorporated herein by reference. Alternatively, video encoder 20 and video decoder 30 may operate according to other proprietary or industrial standards, such as the ITU-T h.264 standard, alternatively referred to as MPEG-4 part 10, Advanced Video Coding (AVC), or extensions of such standards. However, the techniques of this disclosure are not limited to any particular coding standard or technique. Other examples of video compression standards and techniques include MPEG-2, ITU-T H.263, and proprietary or open source compression formats, such as VP8 and related formats.

Although not shown in the example of fig. 1, video encoder 20 and video decoder 30 may each be integrated with an audio encoder and decoder, and may include appropriate MUX-DEMUX units, or other hardware and software, to handle encoding of both audio and video in a common data stream or separate data streams. If applicable, in some examples, the MUX-DEMUX unit may conform to the ITU H.223 multiplexer protocol or other protocols such as the User Datagram Protocol (UDP).

Again, fig. 1 is merely an example, and the techniques of this disclosure may be applicable to video coding settings (e.g., video encoding or video decoding) that do not necessarily include any data communication between an encoding device and a decoding device. In other examples, the data may be retrieved from local memory, streamed over a network, and so on. An encoding device may encode and store data to memory, and/or a decoding device may retrieve and decode data from memory. In many examples, the encoding and decoding are performed by devices that do not communicate with each other, but merely encode and/or retrieve data to and/or from memory and decode the data.

Video encoder 20 and video decoder 30 may each be implemented as any of a variety of suitable circuits such as one or more microprocessors, Digital Signal Processors (DSPs), Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), discrete logic, hardware, or any combinations thereof. When the techniques are implemented in part in software, a device may store instructions for the software in a suitable non-transitory computer-readable storage medium, and may execute the instructions in hardware using one or more processors to perform the techniques of this disclosure. Each of video encoder 20 and video decoder 30 may be included in one or more encoders or decoders, either of which may be integrated as part of a combined encoder/decoder (CODEC) in the respective device.

As briefly mentioned above, video encoder 20 encodes video data. The video data may include one or more pictures. Each of the pictures is a still image that forms part of the video. In some cases, a picture may be referred to as a video "frame. When video encoder 20 encodes the video data, video encoder 20 may generate a bitstream. The bits may comprise a sequence of bits that forms a coded representation of the video data. The bitstream may include coded pictures and associated data. A coded picture is a coded representation of a picture.

To generate the bitstream, video encoder 20 may perform an encoding operation on each picture in the video data. When video encoder 20 performs an encoding operation on a picture, video encoder 20 may generate a series of coded pictures and associated data. The associated data may include sequence parameter sets, picture parameter sets, adaptation parameter sets, and other syntax structures. A Sequence Parameter Set (SPS) may contain parameters applicable to zero or more picture sequences. A Picture Parameter Set (PPS) may contain parameters applicable to zero or more pictures. An Adaptation Parameter Set (APS) may contain parameters applicable to zero or more pictures. The parameters in the APS may be parameters that are more likely to change than the parameters in the PPS.

To generate a coded picture, video encoder 20 may partition the picture into equally sized video blocks. The video blocks may be a two-dimensional array of samples. Each of the video blocks is associated with a treeblock. In some cases, a treeblock may be referred to as a Largest Coding Unit (LCU). The treeblocks of HEVC may be broadly similar to macroblocks of previous standards (e.g., h.264/AVC). However, a treeblock is not necessarily limited to a particular size and may include one or more Coding Units (CUs). Video encoder 20 may use quadtree partitioning to partition the video blocks of a treeblock into video blocks associated with the CU, hence the name "treeblock.

In some examples, video encoder 20 may partition a picture into multiple slices. Each of the slices may include an integer number of CUs. In some cases, a slice includes an integer number of treeblocks. In other cases, the boundary of the slice may be within a tree block.

As part of performing the encoding operation on the picture, video encoder 20 may perform the encoding operation on each slice of the picture. When video encoder 20 performs an encoding operation on a slice, video encoder 20 may generate encoded data associated with the slice. The encoded data associated with a slice may be referred to as a "coded slice".

To generate a coded slice, video encoder 20 may perform an encoding operation on each treeblock in the slice. When video encoder 20 performs an encoding operation on a treeblock, video encoder 20 may generate a coded treeblock. The coded treeblock may include data representing an encoded version of the treeblock.

When video encoder 20 generates a coded slice, video encoder 20 may perform encoding operations (i.e., encode) on treeblocks in the slice, which in this case represent largest coding units, according to a raster scan order. In other words, video encoder 20 may encode the treeblocks of the slice in an order that spans from left to right across the topmost column of treeblocks in the slice, then from left to right across the next column of treeblocks, and so on until video encoder 20 has encoded each of the treeblocks in the slice.

As a result of encoding treeblocks according to a raster scan order, treeblocks above and to the left of a given treeblock may have been encoded, but treeblocks below and to the right of the given treeblock have not yet been encoded. Thus, video encoder 20 may be able to access information generated by encoding treeblocks above and to the left of a given treeblock when encoding the given treeblock. However, video encoder 20 may not be able to access the information generated by encoding treeblocks below and to the right of a given treeblock when encoding the given treeblock.

To generate coded treeblocks, video encoder 20 may recursively perform quadtree partitioning on the video blocks of the treeblocks to divide the video blocks into progressively smaller video blocks. Each of the smaller video blocks may be associated with a different CU. For example, video encoder 20 may partition a video block of a treeblock into four equally sized sub-blocks, partition one or more of the sub-blocks into four equally sized sub-sub-blocks (sub-sub-blocks), and so on. A partitioned CU may be a CU whose video block is partitioned into video blocks associated with other CUs. An undivided CU may be a CU whose video block is undivided into video blocks associated with other CUs.

One or more syntax elements in the bitstream may indicate a maximum number of times video encoder 20 may partition a video block of a treeblock. The video block of a CU may be square in shape. The size of the video block of a CU (i.e., the size of the CU) may vary from 8x8 pixels up to the size of the video block of a treeblock (i.e., the size of the treeblock) of 64x64 pixels or larger at maximum.

Video encoder 20 may perform an encoding operation (i.e., encoding) on each CU of a treeblock according to the z-scan order. In other words, video encoder 20 may encode the top-left CU, the top-right CU, the bottom-left CU, and then the bottom-right CU in that order. When video encoder 20 performs an encoding operation on a partitioned CU, video encoder 20 may encode CUs associated with sub-blocks of a video block of the partitioned CU according to the z-scan order. In other words, video encoder 20 may encode the CU associated with the top-left sub-block, the CU associated with the top-right sub-block, the CU associated with the bottom-left sub-block, and then the CU associated with the bottom-right sub-block in that order.

As a result of encoding CUs of the treeblock according to the z-scan order, CUs above, above-left, above-right, left, and below-left of a given CU may have been encoded. The CUs below or to the right of a given CU have not yet been encoded. Thus, video encoder 20 may be able to access information generated by encoding some CUs that neighbor a given CU when encoding the given CU. However, video encoder 20 may not be able to access information generated by encoding other CUs that neighbor the given CU when encoding the given CU.

When video encoder 20 encodes an undivided CU, video encoder 20 may generate one or more Prediction Units (PUs) for the CU. Each of the PUs of the CU may be associated with a different video block within the video block of the CU. Video encoder 20 may generate a prediction video block for each PU of the CU. The predictive video block of the PU may be a block of samples. Video encoder 20 may generate the predictive video block for the PU using either intra prediction or inter prediction.

When video encoder 20 generates the predictive video block for the PU using intra prediction, video encoder 20 may generate the predictive video block for the PU based on decoded samples of a picture associated with the PU. A CU is an intra-predicted CU if video encoder 20 uses intra-prediction to generate predicted video blocks for PUs of the CU. When video encoder 20 generates the predictive video block for the PU using inter prediction, video encoder 20 may generate the predictive video block for the PU based on decoded samples of one or more pictures other than the picture associated with the PU. A CU is an inter-predicted CU if video encoder 20 uses inter prediction to generate the predictive video blocks for the PUs of the CU.

Moreover, when video encoder 20 generates the predictive video block for the PU using inter-frame prediction, video encoder 20 may generate motion information for the PU. The motion information for the PU may indicate one or more reference blocks of the PU. Each reference block of a PU may be a video block within a reference picture. The reference picture may be a picture other than the picture associated with the PU. In some cases, the reference block of the PU may also be referred to as a "reference sample" of the PU. Video encoder 20 may generate the predictive video block for the PU based on the reference block of the PU.

After video encoder 20 generates the predictive video blocks for the one or more PUs of the CU, video encoder 20 may generate residual data for the CU based on the predictive video blocks for the PUs of the CU. The residual data for the CU may indicate differences between samples in the predictive video blocks for the PUs of the CU and the original video block of the CU.

Moreover, as part of performing encoding operations on an undivided CU, video encoder 20 may perform recursive quadtree partitioning on residual data of the CU to partition the residual data of the CU into one or more blocks of residual data (i.e., residual video blocks) associated with Transform Units (TUs) of the CU. Each TU of a CU may be associated with a different residual video block.

Video encoder 20 may apply one or more transforms to a residual video block associated with a TU to generate a block of transform coefficients (i.e., a block of transform coefficients) associated with the TU. Conceptually, a transform coefficient block may be a two-dimensional (2D) matrix of transform coefficients.

After generating the transform coefficient block, video encoder 20 may perform a quantization process on the transform coefficient block. Quantization generally refers to a process of quantizing transform coefficients to possibly reduce the amount of data used to represent the transform coefficients, thereby providing further compression. The quantization process may reduce the bit depth associated with some or all of the transform coefficients. For example, during quantization, an n-bit transform coefficient may be rounded down to an m-bit transform coefficient, where n is greater than m.

Video encoder 20 may associate each CU with a Quantization Parameter (QP) value. The QP value associated with a CU may determine how video encoder 20 quantizes a transform coefficient block associated with the CU. Video encoder 20 may adjust the degree of quantization applied to the transform coefficient block associated with the CU by adjusting the QP value associated with the CU.

After video encoder 20 quantizes the transform coefficient block, video encoder 20 may generate a set of syntax elements that represent the transform coefficients in the quantized transform coefficient block. Video encoder 20 may apply entropy encoding operations, such as Context Adaptive Binary Arithmetic Coding (CABAC) operations, to some of these syntax elements.

The bitstream generated by video encoder 20 may include a series of Network Abstraction Layer (NAL) units. Each of the NAL units may be a syntax structure that contains an indication of the type of data in the NAL unit and byte containing the data. For example, a NAL unit may contain data representing a sequence parameter set, a picture parameter set, a coded slice, Supplemental Enhancement Information (SEI), an access unit delimiter, filler data (filler data), or another type of data. The data in a NAL unit may include various syntax structures.

Video decoder 30 may receive a bitstream generated by video encoder 20. The bitstream may include a coded representation of the video data encoded by video encoder 20. When video decoder 30 receives the bitstream, video decoder 30 may perform a parsing operation on the bitstream. When video decoder 30 performs a parsing operation, video decoder 30 may extract syntax elements from the bitstream. Video decoder 30 may reconstruct the pictures of the video data based on the syntax elements extracted from the bitstream. The process of reconstructing video data based on syntax elements may generally be reciprocal to the process performed by video encoder 20 to generate syntax elements.

After video decoder 30 extracts the syntax elements associated with the CU, video decoder 30 may generate the predictive video blocks for the PUs of the CU based on the syntax elements. In addition, video decoder 30 may inverse quantize transform coefficient blocks associated with TUs of the CU. Video decoder 30 may perform an inverse transform on the transform coefficient blocks to reconstruct residual video blocks associated with TUs of the CU. After generating the prediction video block and reconstructing the residual video block, video decoder 30 may reconstruct the video block of the CU based on the prediction video block and the residual video block. In this way, video decoder 30 may reconstruct the video block of the CU based on the syntax elements in the bitstream.

As briefly described above, video encoder 20 may use inter prediction to generate the predictive video blocks and motion information for the PUs of the CU. In many cases, the motion information of a given PU may be the same as or similar to the motion information of one or more nearby PUs (i.e., PUs whose video blocks are spatially or temporally nearby to the video block of the given PU). Because nearby PUs often have similar motion information, video encoder 20 may encode the motion information of a given PU with reference to the motion information of the nearby PUs. Encoding motion information for a given PU with reference to motion information of nearby PUs may reduce the number of bits in the bitstream needed to indicate the motion information for the given PU.

Video encoder 20 may encode the motion information for a given PU in various ways with reference to the motion information of nearby PUs. For example, video encoder 20 may indicate that the motion information of a given PU is the same as the motion information of nearby PUs. This disclosure may use the phrase "merge mode" to refer to indicating that the motion information of a given PU is the same as or derivable from the motion information of nearby PUs. In another example, video encoder 20 may calculate a Motion Vector Difference (MVD) for a given PU. The MVD indicates the difference between the motion vector of a given PU and the motion vectors of nearby PUs. In this example, video encoder 20 may include the MVD in the motion information for the given PU instead of the motion vector for the given PU. Fewer bits may be needed in the bitstream to represent an MVD than the motion vector for a given PU. This disclosure may use the phrasal "advanced motion vector prediction" (AMVP) mode to refer to signaling the motion information for a given PU in this manner.

To signal motion information for a given PU using merge mode or AMVP mode, video encoder 20 may generate a candidate list for the given PU. The candidate list may include one or more candidates. Each of the candidates in the candidate list for a given PU may specify motion information. The motion information indicated by the candidates may include motion vectors, reference picture indices, and prediction direction indicators. Candidates in the candidate list may include candidates that are based on (e.g., indicate, are derived from, etc.) motion information of PUs other than the given PU, provided that the other PUs do not belong to CUs associated with the given PU.

After generating the candidate list for the PU, video encoder 20 may select one of the candidates from the candidate list for the PU. Video encoder 20 may output the candidate index for the PU. The candidate index may identify the position of the selected candidate in the candidate list.

Furthermore, video encoder 20 may generate the predictive video block for the PU based on the reference block indicated by the motion information of the PU. The motion information for the PU may be determined based on the motion information indicated by the selected candidate in the candidate list for the PU. For example, in merge mode, the motion information of the PU may be the same as the motion information indicated by the selected candidate. In AMVP mode, the motion information for the PU may be determined based on the motion vector difference for the PU and the motion information indicated by the selected candidate. Video encoder 20 may process the predictive video blocks for the PU, as described above.

When video decoder 30 receives the bitstream, video decoder 30 may generate a candidate list for each of the PUs of the CU. The candidate list generated by video decoder 30 for the PU may be the same as the candidate list generated by video encoder 20 for the PU. The syntax parsed from the bitstream may indicate a location of a selected candidate in the candidate list of PUs. After generating the candidate list for a PU, video decoder 30 may generate a predictive video block for the PU based on one or more reference blocks indicated by motion information of the PU. Video decoder 30 may determine the motion information for the PU based on the motion information indicated by the selected candidate in the candidate list for the PU. Video decoder 30 may reconstruct the video blocks for the CU based on the predictive video blocks for the PU and the residual video blocks for the CU.

While encoding the motion information of the first PU with reference to the motion information of the second PU may reduce the number of bits in the bitstream required to indicate the motion information of the first PU, doing so may prevent video encoder 20 from encoding the motion information of the first PU until video encoder 20 has encoded the motion information of the second PU. Thus, video encoder 20 may not be able to encode the motion information for the first and second PUs in parallel. The ability to encode the motion information for multiple PUs in parallel may increase the throughput of video encoder 20.

Likewise, encoding the motion information of the first PU with reference to the motion information of the second PU may prevent video decoder 30 from determining the motion information of the first PU until video decoder 30 has determined the motion information of the second PU later. Thus, video decoder 30 may not be able to generate prediction blocks for the first and second PUs in parallel. The ability to decode the motion information of multiple PUs in parallel may increase the throughput of video decoder 30.

In accordance with the techniques of this disclosure, video encoder 20 and video decoder 30 may generate a candidate list for each PU of a CU such that each candidate in the candidate list for the PU that is generated based on motion information of at least one other PU is generated without using motion information of any other PU of the same CU. Because candidates are not generated using motion information of any other PU of the same CU, video encoder 20 may encode motion information of multiple PUs of the CU in parallel. Because candidates are not generated using motion information of any other PU of the same CU, video decoder 30 may decode motion information of multiple PUs of the CU in parallel. This may increase the speed at which video encoder 20 may encode video data and video decoder 30 may decode video data.

In this way, a video coder (e.g., video encoder 20 or video decoder 30) may, for each PU of a plurality of PUs belonging to a current CU, generate a candidate list for the PU such that each candidate in the candidate list generated based on motion information of at least one other PU is generated without using motion information of any other PU belonging to the current CU. The video coder may, for each PU belonging to the current CU, generate a predictive video block for the PU based on a reference block indicated by motion information of the PU, the motion information of the PU being determinable based on a motion vector indicated by a selected candidate in the candidate list for the PU.

FIG. 2 is a block diagram illustrating an example video encoder 20 that may be configured to implement the techniques of this disclosure. Fig. 2 is provided for purposes of explanation, and should not be taken as limiting the techniques as broadly illustrated and described in this disclosure. For purposes of explanation, this disclosure describes video encoder 20 in the context of HEVC coding. However, the techniques of this disclosure may be applicable to other coding standards or methods.

In the example of fig. 2, video encoder 20 includes a plurality of functional components. The functional components of video encoder 20 include a prediction module 100, a residual generation module 102, a transform module 104, a quantization module 106, an inverse quantization module 108, an inverse transform module 110, a reconstruction module 112, a filter module 113, a decoded picture buffer 114, and an entropy encoding module 116. The prediction module 100 includes an inter prediction module 121, a motion estimation module 122, a motion compensation module 124, and an intra prediction module 126. In other examples, video encoder 20 may include more, fewer, or different functional components. Furthermore, motion estimation module 122 and motion compensation module 124 may be highly integrated, but are separately represented in the example of fig. 2 for purposes of explanation.

Video encoder 20 may receive video data. Video encoder 20 may receive video data from various sources. For example, video encoder 20 may receive video data from video source 18 (fig. 1) or another source. The video data may represent a series of pictures. To encode the video data, video encoder 20 may perform an encoding operation on each of the pictures. As part of performing the encoding operation on the picture, video encoder 20 may perform the encoding operation on each slice of the picture. As part of performing the encoding operation on the slice, video encoder 20 may perform the encoding operation on the treeblocks in the slice.

As part of performing encoding operations on the treeblocks, prediction module 100 may perform quadtree partitioning on the video blocks of the treeblocks to divide the video blocks into progressively smaller video blocks. Each of the smaller video blocks may be associated with a different CU. For example, prediction module 100 may partition a video block of a treeblock into four equally sized sub-blocks, partition one or more of the sub-blocks into four equally sized sub-blocks, and so on.

The size of the video blocks associated with a CU may vary from 8x8 samples up to a maximum tree block size of 64x64 samples or larger. In this disclosure, "NxN" and "N by N" may be used interchangeably to refer to sample sizes of video blocks in terms of vertical and horizontal dimensions (e.g., 16x16 samples or 16 by 16 samples). In general, a 16x16 video block has sixteen samples in the vertical direction (y =16) and sixteen samples in the horizontal direction (x = 16). Likewise, an NxN block typically has N samples in the vertical direction and N samples in the horizontal direction, where N represents a non-negative integer value.

Further, as part of performing encoding operations on the tree blocks, prediction module 100 may generate a hierarchical quadtree data structure for the tree blocks. For example, a tree block may correspond to a root node of a quadtree data structure. If prediction module 100 partitions the video block of the tree block into four sub-blocks, the root node has four sub-nodes in a quadtree data structure. Each of the sub-nodes corresponds to a CU associated with one of the sub-blocks. If prediction module 100 partitions one of the sub-blocks into four sub-blocks, the node corresponding to the CU associated with the sub-block may have four sub-nodes, each of which corresponds to the CU associated with one of the sub-blocks.

Each node of the quadtree data structure may contain syntax data (e.g., syntax elements) for a corresponding treeblock or CU. For example, a node in the quadtree may include a split flag that indicates whether a video block of the CU corresponding to the node is partitioned (i.e., split) into four sub-blocks. Syntax elements for a CU may be defined recursively and may depend on whether a video block of the CU is split into sub-blocks. A CU whose video block is not partitioned may correspond to a leaf node in a quadtree data structure. The coded treeblock may include data based on a quadtree data structure for the corresponding treeblock.

Video encoder 20 may perform an encoding operation on each undivided CU of a treeblock. When video encoder 20 performs an encoding operation on an undivided CU, video encoder 20 generates data representing an encoded representation of the undivided CU.

As part of performing the encoding operation on the CU, prediction module 100 may partition the video block of the CU among one or more PUs of the CU. Video encoder 20 and video decoder 30 may support various PU sizes. Assuming that the size of a particular CU is 2Nx2N, video encoder 20 and video decoder 30 may support PU sizes of 2Nx2N or NxN for intra prediction, and 2Nx2N, 2NxN, Nx2N, NxN, or similar symmetric PU sizes for inter prediction. Video encoder 20 and video decoder 30 may also support asymmetric partitions of PU sizes of 2NxnU, 2NxnD, nLx2N, and nRx2N for inter-prediction. In some examples, prediction module 100 may perform geometric partitioning to partition the video block of the CU among PUs of the CU along boundaries that do not intersect sides of the video block of the CU at right angles.

Inter prediction module 121 may perform inter prediction on each PU of the CU. Inter-prediction may provide temporal compression. To perform inter prediction for a PU, motion estimation module 122 may generate motion information for the PU. Motion compensation module 124 may generate the predictive video block for the PU based on motion information and decoded samples of pictures other than the picture associated with the CU (i.e., the reference picture).

The slice may be an I slice, a P slice, or a B slice. Motion estimation module 122 and motion compensation module 124 may perform different operations for a PU of a CU depending on whether the PU is in an I-slice, a P-slice, or a B-slice. In I slices, all PUs are intra predicted. Thus, if the PU is in an I-slice, motion estimation module 122 and motion compensation module 124 do not perform inter prediction on the PU.

If the PU is in a P slice, the picture containing the PU is associated with a reference picture list referred to as "list 0". Each of the reference pictures in list 0 contains samples that can be used to inter-predict other pictures. When motion estimation module 122 performs a motion estimation operation with respect to a PU in a P slice, motion estimation module 122 may search for a reference block for the PU in a reference picture in list 0. The reference block of the PU may be a set of samples, e.g., a block of samples, that most closely correspond to samples in the video block of the PU. Motion estimation module 122 may use a variety of metrics to determine how closely a set of samples in a reference picture corresponds to samples in the video block of the PU. For example, motion estimation module 122 may determine how close a set of samples in a reference picture corresponds to samples in the video block of the PU from Sum of Absolute Differences (SAD), Sum of Squared Differences (SSD), or other different metrics.

After identifying the reference block for the PU in the P slice, motion estimation module 122 may generate a reference index indicating the reference picture in list 0 that contains the reference block and a motion vector indicating the spatial displacement between the PU and the reference block. In various examples, motion estimation module 122 may generate motion vectors of varying degrees of precision. For example, motion estimation module 122 may generate motion vectors at quarter sample precision, eighth sample precision, or other fractional sample precision. In the case of fractional sample precision, the reference block value may be interpolated from integer positional sample values in the reference picture. Motion estimation module 122 may output the reference index and the motion vector as the motion information for the PU. Motion compensation module 124 may generate the predictive video block for the PU based on the reference block identified by the motion information of the PU.

If the PU is in a B slice, the picture containing the PU may be associated with two reference picture lists, referred to as "list 0" and "list 1". In some examples, the picture containing the B slice may be associated with a list combination (which is a combination of list 0 and list 1).

Furthermore, if the PU is in a B slice, motion estimation module 122 may perform uni-directional prediction or bi-directional prediction for the PU. When motion estimation module 122 performs uni-directional prediction for a PU, motion estimation module 122 may search for a reference block for the PU in a reference picture of list 0 or list 1. Motion estimation module 122 may then generate a reference index indicating the reference picture in list 0 or list 1 that contains the reference block and a motion vector indicating the spatial displacement between the PU and the reference block. Motion estimation module 122 may output the reference index, the prediction direction indicator, and the motion vector as the motion information for the PU. The prediction direction indicator may indicate whether the reference index indicates a reference picture in list 0 or list 1. Motion compensation module 124 may generate the predictive video block for the PU based on the reference block indicated by the motion information of the PU.

Motion estimation module 122 performs bi-prediction for the PU, and motion estimation module 122 may search for a reference block for the PU in a reference picture in list 0, and may also search for another reference block for the PU in a reference picture in list 1. Motion estimation module 122 may then generate reference indices indicating reference pictures in list 0 and list 1 that contain the reference block and motion vectors indicating spatial displacements between the reference block and the PU. Motion estimation module 122 may output the reference index and the motion vector of the PU as the motion information of the PU. Motion compensation module 124 may generate the predictive video block for the PU based on the reference block indicated by the motion information of the PU.

In some cases, motion estimation module 122 does not output the full set of motion information for the PU to entropy encoding module 116. Instead, motion estimation module 122 may signal the motion information of a PU with reference to the motion information of another PU. For example, motion estimation module 122 may determine that the motion information of the PU is sufficiently similar to the motion information of the neighboring PU. In this example, motion estimation module 122 may indicate a value in a syntax structure associated with the PU that indicates to video decoder 30 that the PU has the same motion information as the neighboring PU or has motion information derivable from the neighboring PU. In another example, motion estimation module 122 may identify motion candidates and Motion Vector Differences (MVDs) associated with neighboring PUs in syntax structures associated with the PUs. The motion vector difference indicates a difference between the motion vector of the PU and the motion vector of the indicated motion candidate. Video decoder 30 may use the motion vector of the indicated motion candidate and the motion vector difference to determine the motion vector of the PU. By referencing the motion information of the motion candidate associated with the first PU when signaling the motion information of the second PU, video encoder 20 may be able to signal the motion information of the second PU using fewer bits.

As described below with respect to fig. 4-6 and 8-15, inter prediction module 121 may generate a candidate list for each PU of the CU. Inter prediction module 121 may generate each candidate list such that each candidate in the candidate list generated based on motion information of at least one other PU is generated without using motion information of any of the PUs belonging to the CU. Thus, inter prediction module 121 may be able to generate candidate lists for two or more PUs of a CU in parallel. Because inter prediction module 121 may be capable of generating candidate lists for two or more PUs of the CU in parallel, inter prediction module 121 may be capable of generating predictive video blocks for two or more of the PUs of the CU in parallel. Moreover, by generating candidate lists for each PU of the CU in this manner, video encoder 20 may enable a video decoder (e.g., video decoder 30) to generate candidate lists for two or more PUs of the CU in parallel and to generate predictive video blocks for two or more PUs of the CU in parallel.

As part of performing the encoding operation on the CU, intra prediction module 126 may perform intra prediction on PUs of the CU. Intra-prediction may provide spatial compression. When intra-prediction module 126 performs intra-prediction on a PU, intra-prediction module 126 may generate prediction data for the PU based on decoded samples of other PUs in the same picture. The prediction data for the PU may include a prediction video block and various syntax data. Intra prediction module 126 may perform intra prediction on PUs in I-slices, P-slices, and B-slices.

To perform intra-prediction for a PU, intra-prediction module 126 may generate multiple sets of prediction data for the PU using multiple intra-prediction modes. When intra-prediction module 126 generates the prediction data set for the PU using the intra-prediction mode, intra-prediction module 126 may extend samples from video blocks of neighboring PUs across video blocks of the PU in a direction and/or gradient associated with the intra-prediction mode. Assuming left-to-right, top-to-bottom coding order for PUs, CUs, and treeblocks, neighboring PUs may be above, above-right, above-left, or to the left of a PU. Intra-prediction module 126 may use various numbers of intra-prediction modes, such as 33 directional intra-prediction modes. In some examples, the number of intra prediction modes may depend on the size of the PU.

Prediction module 100 may select prediction data for the PU from among prediction data for the PU generated by motion compensation module 124 or prediction data for the PU generated by intra prediction module 126. In some examples, prediction module 100 selects prediction data for the PU based on a rate/distortion metric for the set of prediction data.

If prediction module 100 selects the prediction data generated by intra-prediction module 126, prediction module 100 may signal the intra-prediction mode used to generate the prediction data for the PU, i.e., the selected intra-prediction mode. The prediction module 100 may signal the selected intra prediction mode in various ways. For example, it is possible that the selected intra prediction mode is the same as the intra prediction mode of the neighboring PU. In other words, the intra prediction mode of the neighboring PU may be the most likely mode for the current PU. Thus, prediction module 100 may generate a syntax element to indicate that the selected intra-prediction mode is the same as the intra-prediction modes of the neighboring PUs.

After prediction module 100 selects prediction data for PUs of the CU, residual generation module 102 may generate residual data for the CU by subtracting the prediction video blocks of the PUs of the CU from the video blocks of the CU. The residual data of the CU may include 2D residual video blocks that correspond to different sample components of the samples in the video block of the CU. For example, the residual data may include a residual video block that corresponds to a difference between a sample luminance component in a prediction video block of a PU of the CU and a sample luminance component in an original video block of the CU. In addition, the residual data of the CU may include a residual video block that corresponds to a difference between sample chrominance components in the prediction video blocks of the PUs of the CU and sample chrominance components in the original video block of the CU.

Prediction module 100 may perform quadtree partitioning to partition the residual video block of the CU into sub-blocks. Each undivided residual video block may be associated with a different TU of the CU. The size and location of the residual video blocks associated with the TUs of the CU may or may not be based on the size and location of the video blocks associated with the PUs of the CU. A quadtree structure, referred to as a "residual quadtree" (RQT), may include nodes associated with each of the residual video blocks. The TUs of a CU may correspond to leaf nodes of a RQT.

Transform module 104 may generate one or more transform coefficient blocks for each TU of the CU by applying one or more transforms to residual video blocks associated with the TU. Each of the transform coefficient blocks may be a 2D matrix of transform coefficients. Transform module 104 may apply various transforms to residual video blocks associated with TUs. For example, transform module 104 may apply a Discrete Cosine Transform (DCT), a directional transform, or a conceptually similar transform to a residual video block associated with a TU.

After transform module 104 generates a transform coefficient block associated with a TU, quantization module 106 may quantize the transform coefficients in the transform coefficient block. Quantization module 106 may quantize transform coefficient blocks associated with TUs of a CU based on QP values associated with the CU.

Video encoder 20 may associate QP values with CUs in various ways. For example, video encoder 20 may perform rate-distortion analysis on treeblocks associated with CUs. In rate-distortion analysis, video encoder 20 may generate multiple coded representations of a treeblock by performing encoding operations on the treeblock multiple times. Video encoder 20 may associate different QP values with the CU when video encoder 20 generates different encoded representations of the treeblock. Video encoder 20 may signal that a given QP value is associated with a CU when the given QP value is associated with the CU in a coded representation of a treeblock having the lowest rate and distortion metric.

Inverse quantization module 108 and inverse transform module 110 may apply inverse quantization and inverse transform, respectively, to the transform coefficient block to reconstruct a residual video block from the transform coefficient block. Reconstruction module 112 may add the reconstructed residual video block to corresponding samples from one or more prediction video blocks generated by prediction module 100 to generate a reconstructed video block associated with the TU. By reconstructing the video blocks for each TU of the CU in this manner, video encoder 20 may reconstruct the video blocks of the CU.

After reconstruction module 112 reconstructs the video block of the CU, filter module 113 may perform deblocking operations to reduce blocking artifacts in the video block associated with the CU. After performing one or more deblocking operations, filter module 113 may store reconstructed video blocks of the CU in decoded picture buffer 114. Motion estimation module 122 and motion compensation module 124 may use the reference picture containing the reconstructed video block to perform inter prediction on PUs of subsequent pictures. In addition, intra-prediction module 126 may use reconstructed video blocks in decoded picture buffer 114 to perform intra-prediction on other PUs in the same picture as the CU.

Entropy encoding module 116 may receive data from other functional components of video encoder 20. For example, entropy encoding module 116 may receive a transform coefficient block from quantization module 106 and may receive syntax elements from prediction module 100. When entropy encoding module 116 receives the data, entropy encoding module 116 may perform one or more entropy encoding operations to generate entropy encoded data. For example, video encoder 20 may perform a Context Adaptive Variable Length Coding (CAVLC) operation, a CABAC operation, a variable-to-variable (V2V) length coding operation, a syntax-based context adaptive binary arithmetic coding (SBAC) operation, a Probability Interval Partitioning Entropy (PIPE) coding operation, or another type of entropy encoding operation on the data. Entropy encoding module 116 may output a bitstream that includes the entropy encoded data.

As part of performing entropy encoding operations on the data, entropy encoding module 116 may select a context model. If entropy encoding module 116 is performing a CABAC operation, the context model may indicate an estimate of the probability of a particular binary value having a particular value. In the context of CABAC, the term "binary value" is used to refer to the bits of the binarized version of the syntax element.

FIG. 3 is a block diagram illustrating an example video decoder 30 that may be configured to implement the techniques of this disclosure. Fig. 3 is provided for purposes of explanation, and is not limiting of the techniques as broadly illustrated and described in this disclosure. For purposes of explanation, this disclosure describes video decoder 30 in the context of HEVC coding. However, the techniques of this disclosure may be applicable to other coding standards or methods.

In the example of fig. 3, video decoder 30 includes a plurality of functional components. The functional components of video decoder 30 include an entropy decoding module 150, a prediction module 152, an inverse quantization module 154, an inverse transform module 156, a reconstruction module 158, a filter module 159, and a decoded picture buffer 160. Prediction module 152 includes a motion compensation module 162 and an intra-prediction module 164. In some examples, video decoder 30 may perform a decoding pass generally reciprocal to the encoding pass described with respect to video encoder 20 of fig. 2. In other examples, video decoder 30 may include more, fewer, or different functional components.

Video decoder 30 may receive a bitstream that includes encoded video data. The bitstream may include a plurality of syntax elements. When video decoder 30 receives the bitstream, entropy decoding module 150 may perform a parsing operation on the bitstream. As a result of performing a parsing operation on the bitstream, entropy decoding module 150 may extract syntax elements from the bitstream. As part of performing the parsing operation, entropy decoding module 150 may entropy decode entropy-encoded syntax elements in the bitstream. The prediction module 152, inverse quantization module 154, inverse transform module 156, reconstruction module 158, and filter module 159 may perform reconstruction operations that generate decoded video data based on syntax elements extracted from the bitstream.

As discussed above, a bitstream may comprise a series of NAL units. NAL units of a bitstream may include sequence parameter set NAL units, picture parameter set NAL units, SEI NAL units, and the like. As part of performing a parsing operation on the bitstream, entropy decoding module 150 may perform parsing operations that extract and entropy decode sequence parameter sets from sequence parameter sets NAL units, picture parameter sets from and entropy decode picture parameter sets NAL units, SEI data from and entropy decode SEI NAL units, and so on.

In addition, NAL units of a bitstream may include coded slice NAL units. As part of performing a parsing operation on the bitstream, entropy decoding module 150 may perform a parsing operation that extracts and entropy decodes coded slices from coded slice NAL units. Each of the coded slices may include a slice header and slice data. The slice header may contain syntax elements related to the slice. The syntax elements in the slice header may include syntax elements that identify a picture parameter set associated with the picture containing the slice. Entropy decoding module 150 may perform entropy decoding operations (e.g., CABAC decoding operations) on syntax elements in the coded slice header to recover the slice header.

As part of extracting slice data from coded slice NAL units, entropy decoding module 150 may perform a parsing operation that extracts syntax elements from coded CUs in the slice data. The extracted syntax elements may include syntax elements associated with the transform coefficient block. Entropy decoding module 150 may then perform CABAC decoding operations on some of the syntax elements.

After entropy decoding module 150 performs the parsing operation on the non-partitioned CU, video decoder 30 may perform a reconstruction operation on the non-partitioned CU. To perform a reconstruction operation on an undivided CU, video decoder 30 may perform a reconstruction operation on each TU of the CU. By performing a reconstruction operation for each TU of the CU, video decoder 30 may reconstruct a residual video block associated with the CU.

As part of performing reconstruction operations on the TUs, inverse quantization module 154 may inverse quantize (i.e., dequantize) the transform coefficient block associated with the TU. Inverse quantization module 154 may inverse quantize the transform coefficient block in a manner similar to the inverse quantization process proposed for HEVC or defined by the h.264 decoding standard. Inverse quantization module 154 may use a quantization parameter QP of a CU of a transform coefficient block calculated by video encoder 20 to determine a degree of quantization and, likewise, a degree of inverse quantization applied by inverse quantization module 154.

After inverse quantization module 154 inverse quantizes the transform coefficient block, inverse transform module 156 may generate a residual video block for a TU associated with the transform coefficient block. Inverse transform module 156 may apply an inverse transform to the transform coefficient block in order to generate a residual video block for the TU. For example, inverse transform module 156 may apply an inverse DCT, an inverse integer transform, an inverse karhunen-loeve transform (KLT), an inverse rotation transform, an inverse transform, or another inverse transform to the transform coefficient block.

In some examples, inverse transform module 156 may determine an inverse transform to apply to the transform coefficient block based on signaling from video encoder 20. In such examples, the inverse transform module 156 may determine the inverse transform based on a signaled transform at a root node of a quadtree of a treeblock associated with the transform coefficient block. In other examples, inverse transform module 156 may infer the inverse transform from one or more coding characteristics (e.g., block size, coding mode, etc.). In some examples, inverse transform module 156 may apply a cascaded inverse transform.

If the PU of the CU is encoded using inter prediction, motion compensation module 162 may generate a candidate list for the PU. In accordance with the techniques of this disclosure, motion compensation module 162 may generate a candidate list for a PU such that each candidate in the candidate list generated based on motion information of at least one other PU is generated without using motion information of other PUs belonging to the same CU. The bitstream may include data that identifies a location of the selected candidate in the candidate list of the PU. After generating the candidate list for a PU, motion compensation module 162 may generate a predictive video block for the PU based on one or more reference blocks indicated by motion information of the PU. The reference block of the PU may be in a different temporal picture than the PU. Motion compensation module 162 may determine the motion information of the PU based on the motion information indicated by the selected candidate in the candidate list of the PU.

In some examples, motion compensation module 162 may refine the predictive video block of the PU by performing interpolation based on the interpolation filter. An identifier of an interpolation filter to be used for motion compensation with sub-sample precision may be included in the syntax element. Motion compensation module 162 may calculate interpolated values for sub-integer samples of the reference block using the same interpolation filters as used by video encoder 20 during generation of the predictive video block of the PU. Motion compensation module 162 may determine the interpolation filters used by video encoder 20 according to the received syntax information and use the interpolation filters to generate the predictive video block.

If the PU is encoded using intra prediction, intra prediction module 164 may perform intra prediction to generate a predicted video block for the PU. For example, intra-prediction module 164 may determine the intra-prediction mode for the PU based on syntax elements in the bitstream. The bitstream may include syntax elements that intra-prediction module 164 may use to determine the intra-prediction mode of the PU.

In some cases, the syntax element may indicate that intra prediction module 164 is to use the intra prediction mode of another PU to determine the intra prediction mode of the current PU. For example, it may be possible that the intra prediction mode of the current PU is the same as the intra prediction mode of the neighboring PU. In other words, the intra prediction mode of the neighboring PU may be the most likely mode for the current PU. Thus, in this example, the bitstream may include a small syntax element that indicates that the intra-prediction mode of the PU is the same as the intra-prediction mode of the neighboring PU. Intra-prediction module 164 may then generate prediction data (e.g., prediction samples) for the PU based on the video blocks of the spatially neighboring PUs using the intra-prediction mode.

Reconstruction module 158 may reconstruct the video blocks of the CU using residual video blocks associated with the TUs of the CU and prediction video blocks (i.e., intra-prediction data or inter-prediction data) of the PUs of the CU, as appropriate. Thus, video decoder 30 may generate the prediction video block and the residual video block based on syntax elements in the bitstream, and may generate the video block based on the prediction video block and the residual video block.

After reconstruction module 158 reconstructs the video block of the CU, filter module 159 may perform deblocking operations to reduce blocking artifacts associated with the CU. After filter module 159 performs the deblocking operation to reduce blocking artifacts associated with the CU, video decoder 30 may store the video block of the CU in decoded picture buffer 160. Decoded picture buffer 160 may provide reference pictures for subsequent motion compensation, intra prediction, and presentation on a display device (e.g., display device 32 of fig. 1). For example, video decoder 30 may perform intra-prediction or inter-prediction operations on PUs of other CUs based on the video blocks in decoded picture buffer 160.

Fig. 4 is a conceptual diagram illustrating an example configuration of the inter prediction module 121. Inter prediction module 121 may partition the current CU into PUs according to a plurality of partition modes. For example, inter prediction module 121 may partition a current CU into PUs according to 2Nx2N, 2NxN, Nx2N, and NxN partition modes.

Inter prediction module 121 may perform Integer Motion Estimation (IME) and then Fractional Motion Estimation (FME) for each of the PUs. When inter prediction module 121 performs IME on a PU, inter prediction module 121 may search one or more reference pictures for a reference block for the PU. After finding the reference block for the PU, inter prediction module 121 may generate a motion vector that indicates, with integer precision, a spatial displacement between the PU and the reference block for the PU. When inter prediction module 121 performs FME on a PU, inter prediction module 121 may refine a motion vector generated by performing IME on the PU. The motion vectors generated by performing FME on the PU may have sub-integer precision (e.g., 1/2 pixel precision, 1/4 pixel precision, etc.). After generating the motion vector for the PU, inter prediction module 121 may generate the predictive video block for the PU using the motion vector for the PU.

In some examples in which inter prediction module 121 signals motion information for a PU using AMVP mode, inter prediction module 121 may generate a candidate list for the PU. The candidate list may include one or more candidates generated based on motion information of other PUs. For example, the candidate list may include original candidates that indicate motion information of other PUs and/or candidates that indicate motion information derived from motion information of one or more other PUs. After generating the candidate list for the PU, inter prediction module 121 may select a candidate from the candidate list and generate a Motion Vector Difference (MVD) for the PU. The MVD for the PU may indicate a difference between the motion vector indicated by the selected candidate and a motion vector generated for the PU using IME and FME. In such examples, inter-prediction module 121 may output a candidate index that identifies the position of the selected candidate in the candidate list. The inter prediction module 121 may also output the MVD of the PU. FIG. 6, described in detail below, illustrates an example AMVP operation.

In addition to generating motion information for the PUs by performing IME and FME on the PUs, inter prediction module 121 may perform a merge operation on each of the PUs. When inter prediction module 121 performs a merge operation on a PU, inter prediction module 121 may generate a candidate list for the PU. The candidate list for the PU may include one or more original candidates. The original candidates in the candidate list may include one or more spatial candidates and temporal candidates. The spatial candidates may indicate motion information of other PUs in the current picture. The temporal candidates may be based on motion information of collocated PUs of pictures other than the current picture. The temporal candidates may also be referred to as Temporal Motion Vector Predictors (TMVP).

After generating the candidate list, the inter prediction module 121 may select one of the candidates from the candidate list. Inter prediction module 121 may then generate a predictive video block for the PU based on the reference block indicated by the motion information of the PU. In merge mode, the motion information of the PU may be the same as the motion information indicated by the selected candidate. FIG. 5, described below, is a flow diagram illustrating an example merge operation.

After generating the predictive video blocks for the PU based on the IME and FME and after generating the predictive video blocks for the PU based on the merge operation, inter prediction module 121 may select either the predictive video blocks generated by the FME operation or the predictive video blocks generated by the merge operation. In some examples, inter prediction module 121 may select a prediction video block for the PU based on rate/distortion analysis of the prediction video blocks generated by the FME operation and the prediction video blocks generated by the merge operation.

After the inter-prediction module 121 has selected the predictive video block for the PU that was generated by partitioning the current CU according to each of the partition modes, the inter-prediction module 121 may select the partition mode for the current CU. In some examples, inter prediction module 121 may select the partitioning mode for the current CU based on a rate/distortion analysis of a selected predictive video block for the PU generated by partitioning the current CU according to each of the partitioning modes. Inter prediction module 121 may output the predictive video blocks associated with PUs belonging to the selected partition mode to residual generation module 102. Inter prediction module 121 may output syntax elements indicating motion information for PUs belonging to the selected partition mode to entropy encoding module 116.

In the example of fig. 4, the inter-prediction module 121 includes IME modules 180A-180N (collectively, "IME modules 180"), FME modules 182A-182N (collectively, "FME modules 182"), merge modules 184A-184N (collectively, "merge modules 184"), PU mode decision modules 186A-186N (collectively, "PU mode decision modules 186"), and a CU mode decision module 188.

IME module 180, FME module 182, and merge module 184 may perform IME operations, FME operations, and merge operations on PUs of the current CU. The example of fig. 4 illustrates the inter prediction module 121 as including a separate IME module 180, FME module 182, and merge module 184 for each PU of each partition mode of the CU. In other examples, the inter-prediction module 121 does not include a separate IME module 180, FME module 182, and merge module 184 for each PU of each partition mode of the CU.

As illustrated in the example of fig. 4, IME module 180A, FME module 182A and merge module 184A may perform IME operations, FME operations, and merge operations on PUs generated by partitioning CUs according to a 2Nx2N partitioning pattern. PU mode decision module 186A may select one of the predictive video blocks generated by IME module 180A, FME module 182A and merge module 184A.

The IME module 180B, FME module 182B and the merge module 184B may perform an IME operation, an FME operation, and a merge operation on a left PU generated by partitioning a CU according to the Nx2N partitioning pattern. PU mode decision module 186B may select one of the predictive video blocks generated by IME module 180B, FME module 182B and merge module 184B.

The IME module 180C, FME module 182C and the merge module 184C may perform an IME operation, an FME operation, and a merge operation on a right PU generated by partitioning a CU according to the Nx2N partitioning pattern. PU mode decision module 186C may select one of the predictive video blocks generated by IME module 180C, FME module 182C and merge module 184C.

IME module 180N, FME module 182N and merge module 184 may perform IME, FME, and merge operations on the bottom right PU generated by partitioning a CU according to an NxN partitioning mode. The PU mode decision module 186N may select one of the predictive video blocks generated by the IME module 180N, FME module 182N and the merge module 184N.

After PU mode decision module 186 selects the predictive video block for the PU of the current CU, CU mode decision module 188 selects the partition mode for the current CU and outputs the predictive video blocks and motion information for the PUs belonging to the selected partition mode.

FIG. 5 is a flow diagram illustrating an example merge operation 200. A video encoder, such as video encoder 20, may perform merge operation 200. In other examples, the video encoder may perform a merge operation in addition to merge operation 200. For example, in other examples, the video encoder may perform a merge operation in which the video encoder performs more, less, or different steps than merge operation 200. In other examples, the video encoder may perform the steps of the merge operation 200 in a different order or in parallel. The encoder may also perform the merge operation 200 on PUs encoded in skip mode.

After the video encoder begins the merge operation 200, the video encoder may generate a candidate list for the current PU (202). The video encoder may generate the candidate list for the current PU in various ways. For example, the video encoder may generate the candidate list for the current PU according to one of the example techniques described below with respect to fig. 8-15.

As discussed briefly above, the candidate list for the current PU may include temporal candidates. The temporal candidates may indicate motion information of collocated PUs. Collocated PUs may be spatially collocated with a current PU, but in a reference picture rather than in the current picture. This disclosure may refer to reference pictures that include collocated PUs as related reference pictures. This disclosure may refer to a reference picture index of a related reference picture as a related reference picture index. As described above, a current picture may be associated with one or more reference picture lists (e.g., list 0, list 1, etc.). The reference picture index may indicate the reference picture by indicating a position of the reference picture in one of the reference picture lists. In some examples, the current picture may be associated with a combined reference picture list.

In some conventional video encoders, the relevant reference picture index is the reference picture index of the PU that encompasses the reference index source location associated with the current PU. In such conventional video encoders, the reference index source location associated with the current PU is immediately to the left of or immediately above the current PU. In this disclosure, a PU may "cover" a particular location if the video block associated with the PU includes the particular location. In such conventional video encoders, if a reference index source location is not available, the video encoder may use the reference picture index zero.

However, there may be instances where the reference index source location associated with the current PU is within the current CU. In such cases, a PU that covers the reference index source location associated with the current PU may be considered available if such PU is above or to the left of the current CU. However, the video encoder may need to access motion information of another PU of the current CU in order to determine the reference picture containing the collocated PU. Thus, such conventional video encoders may use motion information (i.e., reference picture indices) of PUs belonging to the current CU to generate temporal candidates for the current PU. In other words, such conventional video encoders may generate temporal candidates using motion information of PUs belonging to the current CU. Thus, the video encoder may not be able to generate candidate lists for the current PU and the PU that covers the reference index source location associated with the current PU in parallel.

According to the techniques of this disclosure, a video encoder may explicitly set a relevant reference picture index without referring to the reference picture index of any other PU. This may enable the video encoder to generate candidate lists for the current PU and other PUs of the current CU in parallel. Because the video encoder explicitly sets the relevant reference picture index, the relevant reference picture index is not based on motion information of any other PU of the current CU. In some examples where the video encoder explicitly sets the relevant reference picture index, the video encoder may always set the relevant reference picture index to a fixed predefined default reference picture index, such as 0. In this way, the video encoder may generate temporal candidates based on motion information of collocated PUs in the reference frame indicated by the default reference picture index, and may include the temporal candidates in the candidate list of the current CU.

In examples where the video encoder explicitly sets the relevant reference picture index, the video encoder may explicitly signal the relevant reference picture index in a syntax structure (e.g., a picture header, a slice header, an APS, or another syntax structure). In this example, the video encoder may signal the relevant reference picture index for each LCU, CU, PU, TU, or another type of sub-block. For example, the video encoder may signal that the relevant reference picture index for each PU of the CU is equal to "1".

In some examples, such as the examples described below with reference to fig. 9A-9F and 10A-10F, the relevant reference picture index may be set implicitly rather than explicitly. In such examples, the video encoder may generate each temporal candidate in the candidate list for a PU of the current CU using motion information of PUs in reference pictures indicated by reference picture indices of PUs that encompass locations outside the current CU, even if such locations are not strictly adjacent to the current PU (i.e., the PU of the current CU).

After generating the candidate list for the current PU, the video encoder may generate a prediction video block associated with a candidate in the candidate list (204). The video encoder may generate a predictive video block associated with the candidate by determining motion information for the current PU based on the motion information for the indicated candidate and then generating the predictive video block based on one or more reference blocks indicated by the motion information for the current PU. The video encoder may then select one of the candidates from the candidate list (206). The video encoder may select the candidates in various ways. For example, the video encoder may select one of the candidates based on a rate/distortion analysis of each of the predictive video blocks associated with the candidate.

After selecting the candidate, the video encoder may output a candidate index (208). The candidate index may indicate a position of the selected candidate in the candidate list. In some examples, the candidate index may be denoted as "merge _ idx".

Fig. 6 is a flow diagram illustrating an example AMVP operation 210. A video encoder, such as video encoder 20, may perform AMVP operation 210. Fig. 6 is only one example of AMVP operation.

After the video encoder begins AMVP operation 210, the video encoder may generate one or more motion vectors for the current PU (211). The video encoder may perform integer motion estimation and fractional motion estimation to generate a motion vector for the current PU. As described above, the current picture may be associated with two reference picture lists (list 0 and list 1). If the current PU is uni-directionally predicted, the video encoder may generate a list 0 motion vector or a list 1 motion vector for the current PU. The list 0 motion vector may indicate a spatial displacement between the video block of the current PU and a reference block in a reference picture in list 0. The list 1 motion vector may indicate a spatial displacement between a video block of the current PU and a reference block in a reference picture in list 1. If the current PU is bi-predicted, the video encoder may generate a list 0 motion vector and a list 1 motion vector for the current PU. After generating one or more motion vectors for the current PU, the video encoder may generate a predictive video block for the current PU (212). The video encoder may generate a predictive video block for the current PU based on one or more reference blocks indicated by one or more motion vectors for the current PU.

In addition, the video encoder may generate a candidate list for the current PU (213). Each candidate in the candidate list generated based on motion information of at least one other PU is generated without using motion information of any other PU belonging to the current CU. The video coder may generate the candidate list for the current PU in various ways. For example, the video encoder may generate the candidate list for the current PU according to one or more of the example techniques described below with respect to fig. 8-15. In some examples, when the video encoder generates the candidate list in AMVP operation 210, the candidate list may be limited to two candidates. In contrast, when the video encoder generates the candidate list in the merge operation, the candidate list may include more candidates (e.g., five candidates).

After generating the candidate list for the current PU, the video encoder may generate one or more Motion Vector Differences (MVDs) for each candidate in the candidate list (214). The video encoder may generate a motion vector difference for the candidate by determining a difference between the motion vector indicated by the candidate and a corresponding motion vector of the current PU.

If the current PU is uni-directionally predicted, the video encoder may generate a single MVD for each candidate. If the current PU is bi-directionally predicted, the video encoder may generate two MVDs for each candidate. The first MVD may indicate a difference between the candidate motion vector and the list 0 motion vector of the current PU. The second MVD may indicate a difference between the candidate motion vector and the list 1 motion vector of the current PU.

The video encoder may select one or more of the candidates from the candidate list (215). The video encoder may select one or more candidates in various ways. For example, the video encoder may select one of the candidates based on the number of bits needed to represent the motion vector difference for the candidate.

After selecting the one or more candidates, the video encoder may output one or more reference picture indices for the current PU, one or more candidate indices, and one or more motion vector differences for the one or more selected candidates (216).

In the case where the current picture is associated with two reference picture lists (list 0 and list 1) and the current PU is uni-directionally predicted, the video encoder may output a reference picture index for list 0 ("ref _ idx _ l 0") or a reference picture index for list 1 ("ref _ idx _ l 1"). The video encoder may also output a candidate index ("mvp _ l0_ flag") indicating the position in the candidate list of the selected candidate for the list 0 motion vector for the current PU. Alternatively, the video encoder may output a candidate index ("mvp _ l1_ flag") indicating the position in the candidate list of the selected candidate for the list 1 motion vector for the current PU. The video encoder may also output an MVD for the list 0 motion vector or the list 1 motion vector of the current PU.

In the case where the current picture is associated with two reference picture lists (list 0 and list 1) and the current PU is bi-directionally predicted, the video encoder may output a reference picture index for list 0 ("ref _ idx _ l 0") and a reference picture index for list 1 ("ref _ idx _ l 1"). The video encoder may also output a candidate index ("mvp _ l0_ flag") indicating the position in the candidate list of the selected candidate for the list 0 motion vector for the current PU. In addition, the video encoder may output a candidate index ("mvp _ l1_ flag") indicating the position in the candidate list of the selected candidate for the list 1 motion vector for the current PU. The video encoder may also output an MVD for the list 0 motion vector for the current PU and an MVD for the list 1 motion vector for the current PU.

Fig. 7 is a flow diagram illustrating an example motion compensation operation 220 performed by a video decoder, such as video decoder 30. Fig. 7 is only one example motion compensation operation.

When the video decoder performs motion compensation operation 220, the video decoder may receive an indication of the selected candidate for the current PU (222). For example, the video decoder may receive a candidate index indicating a position of the selected candidate within the candidate list of the current PU.

If the motion information of the current PU is encoded using AMVP mode and the current PU is bi-directionally predicted, the video decoder may receive a first candidate index and a second candidate index. The first candidate index indicates the position in the candidate list of the selected candidate for the list 0 motion vector for the current PU. The second candidate index indicates a position in the candidate list of the selected candidate for the list 1 motion vector of the current PU.

In addition, the video decoder may generate a candidate list for the current PU (224). According to the techniques of this disclosure, a video decoder may generate a candidate list such that each candidate in the candidate list generated based on motion information of at least one other PU is generated without using motion information of any other PU belonging to the current CU. The video decoder may generate this candidate list for the current PU in various ways. For example, the video decoder may use the techniques described below with respect to fig. 8-15 to generate the candidate list for the current PU. When the video decoder generates temporal candidates for the candidate list, the video decoder may explicitly or implicitly set a reference picture index that identifies the reference picture that includes the collocated PU, as described above with respect to fig. 5.

In some examples, a video coder (e.g., a video encoder or a video decoder) may adapt the size of the candidate list for a CU based on PU size, PU shape, PU index, information about neighboring video blocks, and/or other information. The information about the neighboring video block may include a prediction mode of the neighboring video block, a motion vector difference of the neighboring video block, a reference picture index of the neighboring video block, a prediction direction of the neighboring video block, transform coefficients of the neighboring video block, and/or other information about the neighboring video block. For example, for a CU with a 2NxN mode, the original candidates for the second PU located within the first PU may be removed from the candidate list. As a result, in this case, the size of the candidate list for the second PU may be smaller than the size of the candidate list for the first PU.

In some examples, the video coder may adapt the order of the candidate lists for the PUs based on PU size, PU shape, PU index, information about neighboring video blocks, and/or other information. The information about the neighboring video block may include a prediction mode of the neighboring video block, a motion vector difference of the neighboring video block, a reference picture index of the neighboring video block, a prediction direction of the neighboring video block, transform coefficients of the neighboring video block, and/or other information about the neighboring video block. For example, when generating a merge candidate list based on motion information of PUs that are outside of the current CU, the order of the candidates in the candidate list may be adjusted for each PU. For those candidates located farther from the PU, their order in the list may be decreased relative to candidates closer to the PU. As a result, although the same set of candidates is used to form the candidate list for each PU, the order of the candidates in the list may differ for each PU in the CU due to different PU positions relative to the candidates.

After generating the candidate list for the current PU, the video decoder may determine motion information for the current PU based on the motion vectors indicated by the one or more selected candidates in the candidate list for the current PU (225). For example, if the motion information of the current PU is encoded using merge mode, the motion information of the current PU may be the same as the motion information indicated by the selected candidate. If the motion information of the current PU is encoded using AMVP mode, the video decoder may reconstruct one or more motion vectors of the current PU using one or more motion vectors indicated by the one or more selected candidates and one or more MVDs indicated in the bitstream. The reference picture index and the prediction direction indicator for the current PU may be the same as the reference picture index and the prediction direction indicator for the one or more selected candidates.

After determining the motion information for the current PU, the video decoder may generate a predictive video block for the current PU based on one or more reference blocks indicated by the motion information of the current PU (226).

In fig. 8A and 8B, all PUs of a CU share a single merge candidate list, which may be the same as the merge candidate list of a 2Nx2N PU. Thus, in fig. 8A and 8B, the video coder may generate a merge candidate list that is shared by all PUs of the current CU. In this way, the current CU may be partitioned into multiple PUs according to a selected partitioning mode (e.g., 2NxN, Nx2N, NxN, etc.) other than the 2Nx2N partitioning mode, and motion information for each of the PUs may be determined based on the motion information indicated by the selected candidate in the merge candidate list. The video coder may generate a shared merge list for multiple PUs in the same manner as if the CU was partitioned in the 2Nx2N mode. In other words, the merging candidate list is the same as the candidate list that would be generated if the current CU had been partitioned according to the 2Nx2N partitioning mode. One advantage of this scheme may be that only one merge list may be generated for each CU, regardless of how many PUs the CU has. In addition, based on this approach, motion estimation for different PUs in the same CU may be done in parallel. In this example, the merge list shared by all PUs of the CU may be generated in the same manner as in the case where the CU is partitioned according to the 2Nx2N partitioning mode. Fig. 8A and 8B are examples of generating a merge candidate list without using motion information of PUs of a current CU and sharing the same merge candidate list by all PUs of the current CU.

FIG. 8A is a conceptual diagram illustrating CU250 and example source locations 252A-252E associated with CU 250. The present invention may collectively refer to source locations 252A through 252E as source locations 252. Source location 252A is to the left of CU 250. Source location 252B is located above CU 250. Source location 252C is located to the upper right of CU 250. Source location 252D is located to the lower left of CU 250. Source location 252E is located to the top left of CU 250. Each of the source locations 252 is outside of CU 250.

CU250 may include one or more PUs. The video coder may generate motion candidates for each of the PUs of CU250 based on the motion information of the PU that encompasses source location 252. In this way, the video coder may generate a candidate list for the PU of CU250 such that each candidate generated based on the motion information of at least one other PU is generated without using the motion information of any other PU belonging to CU 250. Generating the candidate lists for the PUs of CU250 in this manner may enable the video coder to generate the candidate lists for multiple PUs of CU250 in parallel.

FIG. 8B is a conceptual diagram illustrating CU260 and example source locations 262A-262G associated with CU 260. The present invention may collectively refer to source locations 262A through 262G as source locations 262. The example of FIG. 8B is similar to the example of FIG. 8A, except that CU260 is associated with seven source locations, rather than five as shown in FIG. 8A. In the example of fig. 8B, the video coder may generate a candidate list for each PU of CU260 based on motion information of one or more PUs that encompass source location 262.

Fig. 9A is a conceptual diagram illustrating an example reference index source location to the left of a 2NxN partitioned CU 300. The PU302 and the PU304 belong to the CU 300. In the example of fig. 9A, reference index source location 306 is associated with PU 302. The reference index source location 308 is associated with the PU 304.

Fig. 9B is a conceptual diagram illustrating an example reference index source location to the left of Nx2N CU 340. PU342 and PU344 belong to CU 340. In the example of fig. 9B, reference index source location 348 is associated with both PU342 and PU 344.

Fig. 9C is a conceptual diagram illustrating an example reference index source location above a 2NxN partitioned CU 320. PU322 and PU324 belong to CU 320. In the example of fig. 9C, reference index source location 328 is associated with PU322 and PU 324.

Fig. 9D is a conceptual diagram illustrating an example reference index source location above Nx2N CU 360. PU362 and PU364 belong to CU 360. In the example of fig. 9D, reference index source location 366 is associated with PU 362. Reference index source location 368 is associated with PU 364.

Fig. 9E is a conceptual diagram illustrating an example reference index source location to the left of an example NxN partitioned CU 400. CU400 is partitioned into PUs 402, 404, 406, and 408. Reference index source location 410 is associated with PU402 and PU 404. Reference index source location 412 is associated with PU406 and PU 408.

Fig. 9F is a conceptual diagram illustrating an example reference index source location above an NxN partitioned CU 420. CU420 is partitioned into PUs 422, 424, 426, and 428. Reference index source location 430 is associated with PU422 and PU 426. Reference index source location 432 is associated with PU426 and PU 428.

As illustrated in the examples of fig. 9A-9F, if the original reference index source location associated with the current PU is within the current CU, then, in accordance with the techniques of this disclosure and instead of using the original reference index source location, the video coder may identify a location outside the current CU that corresponds to the original reference index source location associated with the current PU. A location outside the current CU may correspond to an original reference index source location within the current CU (e.g., both below left, above, or above right of the current PU) based on a criterion that the location is spatially positioned in the same manner relative to the current PU. The video coder may infer that the relevant reference picture index is equal to the reference picture index of a PU that covers the corresponding location outside of the current CU. In this way, the coder may determine the relevant reference picture index without using the motion information of any other PU within the current CU.

As illustrated in the example of fig. 9C, location 326, which is immediately above PU324, is within CU 320. Instead of using the reference picture index of a PU that covers position 326, the video coder may use the reference picture index of a PU that covers the corresponding position outside of CU320 (i.e., reference index source position 328). Similarly, in the example of FIG. 9B, location 346 immediately to the left of PU344 is within CU 340. Instead of using the reference picture index of the PU that covers position 346, the video coder may use the reference picture index of the PU that covers the corresponding position outside of CU340 (i.e., reference index source position 348). In some examples, the corresponding location outside the current CU is spatially located relative to the current PU in the same manner as the original location within the current CU.

Thus, in response to determining that the reference index source location associated with the current PU is within the current CU, the video coder may identify a corresponding location outside of the current CU. The video coder may then generate temporal candidates based on motion information of collocated PUs in the reference picture indicated by PUs covering corresponding locations outside the current CU. The video coder may then include temporal candidates in the candidate list for the current CU.

Fig. 10A is a conceptual diagram illustrating an example reference index source location to the left of a 2NxN partitioned CU 500. The PU502 and the PU504 belong to the CU 500. Fig. 10B is a conceptual diagram illustrating an example reference index source location to the left of an Nx 2N-partitioned CU 520. PU522 and PU524 belong to CU 520. Fig. 10C is a conceptual diagram illustrating an example reference index source location above a 2NxN partitioned CU 540. PU542 and PU544 belong to CU 540. Fig. 10D is a conceptual diagram illustrating an example reference index source location above an Nx 2N-partitioned CU 560. PU562 and PU564 belong to CU 560. Fig. 10E is a conceptual diagram illustrating an example reference index source location to the left of an NxN partitioned CU 580. CU580 is partitioned into PUs 582, 584, 586, and 588. Fig. 10F is a conceptual diagram illustrating an example reference index source location to the left of an NxN partitioned CU 600. CU600 is partitioned into PUs 602, 604, 606, and 608.

Fig. 10A-10F are similar to fig. 9A-9F in that the video coder may be configured to determine, from a PU that encompasses a reference index source location associated with the current PU, a relevant reference picture index for the current PU. However, unlike the examples of fig. 9A-9F, each PU of a CU is associated with the same reference index source location. In other words, the reference picture indices for all PUs in a CU may be derived from a single neighboring block outside the CU.

For example, in the example of fig. 10A, both PUs 502 and 504 are associated with a reference index source location 506 to the left of CU 500. In contrast, in the example of FIG. 9A, PUs 302 and 304 are associated with reference index source locations 306 and 308. Similarly, in the example of fig. 10D, both PU562 and PU564 are associated with a single reference index source location 566 above CU 560. In the example of fig. 10E, PUs 582, 584, 586 and 588 are associated with a single reference index source location 590 located to the left of CU 580. In the example of fig. 10F, PUs 602, 604, 606, and 608 are associated with a single reference index source location 610 that is located above CU 600.

In other examples, the video coder may determine the reference picture index of the temporal candidate for each PU of the CU from any other PU that is spatially outside the CU. For example, the video coder may determine, from PUs located to the left of the CU, above-left of the CU, above-right of the CU, or below-left of the CU, reference picture indices for temporal candidates for each PU of the CU. Coding information within a current CU using a single or multiple source locations outside the current CU may be applicable to the current CU or other types of blocks or at different levels.

FIG. 11 is a flow diagram illustrating example operations 700 to generate time candidates for a PU. A video coder (e.g., video encoder 20 or video decoder 30) may perform operation 700. FIG. 11 is merely one example of operations to generate temporal candidates for a PU.

After the video coder begins operation 700, the video coder may determine whether a PU that encompasses a reference index source location associated with the current PU is available (702). This disclosure may refer to a PU that encompasses a reference index source location as a reference index source PU. The reference index source PU may not be available for various reasons. For example, a reference index source PU may not be available if the reference index source PU is not within the current picture. In another example, a reference index source PU may not be available if the reference index source PU is intra-predicted. In another example, a reference index source PU may not be available if the reference index source PU is in a different slice than the current PU.

In response to determining that a reference index source PU for the current PU is available ("yes" of 702), the video coder may generate temporal candidates that indicate motion information of collocated PUs in reference pictures indicated by reference picture indices of the reference index source PU (704). For example, in the example of fig. 9C, the PU covering location 328 may be the reference index source PU for PU 324. In this case, the video coder may generate temporal candidates for PU324 that indicate motion information of collocated PUs in the reference picture indicated by the reference picture index of the PU covering position 328.

In response to determining that a reference index source PU for the current PU is not available ("no" of 702), the video coder may search for available PUs among PUs that are spatially neighboring the current CU (706). If the video coder does not find an available PU ("no" of 708), the video coder may generate a temporal candidate that indicates motion information for a collocated PU in the reference picture indicated by the default reference picture index (710). For example, if the video coder does not find an available PU, the video coder may generate a temporal candidate for the current PU from a collocated PU in a reference picture indicated by a reference picture index equal to 0, 1, or another number selected by default.

On the other hand, if the video coder finds an available PU ("yes" of 708), the video coder may generate a temporal candidate that indicates motion information of a collocated PU in the reference pictures indicated by the reference picture indices of the available PU (712). For example, if the reference picture index of an available PU is equal to 1, the video coder may generate a temporal candidate that indicates motion information of a collocated PU in the reference picture indicated by reference picture index 1.

In another example, if a reference index source PU is not available, the video coder may generate a temporal candidate that indicates motion information of a collocated PU in a reference picture indicated by the default reference picture index. In this example, the default reference picture index may be a default value (e.g., zero) or may be signaled in a picture parameter set, a slice header, an APS, or another syntax structure.

Thus, in the example of fig. 11, the video coder may search for available PUs that spatially neighbor the current CU in response to determining that the reference index source PU is not available. The video coder may then generate temporal candidates based on motion information of collocated PUs in the reference pictures indicated by the reference picture indices of the available PUs. The video coder may include temporal candidates in the candidate list for the current PU.

Fig. 12 is a flow diagram illustrating example operations 800 to generate a candidate list for a PU. A video coder (e.g., video encoder 20 or video decoder 30) may perform operation 800. FIG. 12 is merely one example of an operation to generate a candidate list for a PU.

After the video coder begins operation 800, the video coder may generate spatial candidates based on motion information of PUs that are spatially neighboring the current PU and outside the current CU (802). In this way, candidates within the current CU are excluded from the candidate list. For example, for the upper right PU of an NxN partitioned CU, the left candidate (L) and the lower left candidate (BL) are excluded from their candidate lists. For the lower left PU of an NxN partitioned CU, the upper candidate (a) and the upper right candidate (RA) are excluded from the candidate list. For the bottom-right PU of an NxN-partitioned CU, three candidates, including the left candidate (L), the above candidate (a), and the top-left candidate (LA), are excluded from the candidate list.

The video coder may then add the spatial candidate to the candidate list for the current PU (804). In addition, the video coder may generate temporal candidates that indicate motion information for collocated PUs in the reference picture (806). The video coder may then add the temporal candidate to the candidate list for the current PU (808).

The video coder may perform operation 800 when the motion information for the current PU is signaled in merge mode. The video coder may also perform operation 800 or the like when the motion information for the current PU is signaled in AMVP mode. In the example where the current CU is signaled in AMVP mode, the candidates in the candidate list may be AMVP candidates.

In this way, the video coder may generate spatial candidates based on motion information of PUs that spatially neighbor the current PU and are outside the current CU. The video coder may then include spatial candidates in the candidate list for the current PU.

Fig. 13 is a flow diagram illustrating example operations 850 to generate a candidate list for a PU. A video coder (e.g., video encoder 20 or video decoder 30) may perform operation 850. FIG. 13 is merely one example of an operation to generate a candidate list for a PU.

After the video coder begins operation 850, the video coder may generate spatial candidates for the current PU based on motion information of PUs that are spatially neighboring the current CU (852). The video coder may then add the spatial candidates to a candidate list for the current PU (854). In the example of fig. 13, the video coder may replace spatial candidate source locations that neighbor the current PU but are within the current CU with corresponding spatial candidate source locations that are outside the current CU. Thus, the locations used by the video coder to generate spatial candidates in fig. 13 are moved to (i.e., replaced with.) corresponding locations outside the current CU. The corresponding position outside the current CU may be located at any neighboring block position: left, above, left-above, right-above, left-below of the current CU. Thus, instead of removing dependent candidates from the candidate list (as described above with respect to fig. 12), the candidates may be taken from neighboring CUs that are located outside the current CU. 14A, 14B, 15A, 15B, 15C, and 15D illustrate spatial candidate source locations used by a video coder to generate spatial candidates according to operation 850.

In some examples, if the spatial candidate source location that neighbors the current PU is not within the current CU and the corresponding PU (i.e., the PU that covers the spatial candidate source location) is unavailable, the video coder may perform a search process among the neighboring PUs to find an available PU. If the video coder is able to find an available PU, the video coder may generate a spatial candidate based on the motion information of the available PU. Alternatively, if the spatial candidate source location that neighbors the current PU is not within the current CU and the corresponding PU (i.e., the PU that covers the spatial candidate source location) is unavailable, the video coder may generate a spatial candidate having a default value (e.g., zero). The default value may be signaled in the PPS, slice header, APS, or another type of header.

In addition, the video coder may generate temporal candidates for the current PU (856). The video coder may then add the temporal candidate to the candidate list for the current PU (858).

The video coder may perform operation 850 when the motion information for the current PU is signaled in merge mode. The video coder may also perform operation 850 or a similar operation when the motion information for the current PU is signaled in AMVP mode. In the example where the current CU is signaled in AMVP mode, the candidates in the candidate list may be AMVP candidates.

In the example of fig. 13, the set of spatial candidate source locations for the current CU may initially include a first spatial candidate source location below and to the left of the current PU, a second spatial candidate source location to the left of the current PU, a third spatial candidate source location above and to the left of the current PU, a fourth spatial candidate source location above the current PU, and a fifth spatial candidate source location above and to the right of the current PU. The video coder may replace any of the spatial candidate source locations within the current CU with corresponding spatial candidate source locations outside of the current CU. The video coder may then generate spatial candidates based on the motion information of the PU that encompasses the spatial candidate source location, and include the spatial candidates in the candidate list for the current PU.

Fig. 14A is a conceptual diagram illustrating example spatial candidate source locations associated with a right PU of an example Nx 2N-partitioned CU 900. PU902 and PU904 belong to CU 900. The video coder may generate spatial candidates for PU904 based on motion information of PUs that encompass spatial candidate source locations 906, 908, 910, 914, and 918. The spatial candidate source locations 906 are located at the top left of the PU 904. The spatial candidate source locations 908 are located above the PU 904. The spatial candidate source location 910 is located in the upper right of the PU 904. The spatial candidate source locations 914 are located below and to the left of the PU 904. Location 916 is spatially located to the left of PU 904. However, rather than using the motion information of the PU encompassing position 916 (i.e., PU902), the video coder may use the motion information of the PU encompassing spatial candidate source position 918 to generate spatial candidates for PU 904. The spatial candidate source location 918 is spatially to the left of the CU 900.

Fig. 14B is a conceptual diagram illustrating example spatial candidate source locations associated with a lower PU of a 2NxN partitioned CU 920. PU922 and PU924 belong to CU 920. The video coder may generate spatial candidates for PU922 based on spatial candidate source locations that are spatially above-left, above-right, left, and below-left of PU 922. Because the location of PU922 is within CU920, none of such spatial candidate source locations are within CU 920. Thus, the video coder is not required to "move" any of the spatial candidate source locations associated with PU922 to generate spatial candidates for PU922 based on motion information of PUs outside of CU 920.

The video coder may generate spatial candidates for PU924 based on spatial candidate source locations 926, 928, 932, 934, and 936. The spatial candidate source location 928 is located to the upper right of the PU 924. The spatial candidate source locations 932 are spatially located below and to the left of the PU 924. The spatial candidate source locations 934 are spatially located to the left of the PU 924. The spatial candidate source locations 936 are spatially above and to the left of the PU 924.

Location 938 is spatially above PU 924. However, location 938 is located within CU 920. Thus, rather than using the motion information of the PU encompassing position 938 (i.e., PU922), the video coder may generate spatial motion candidates for PU924 based on the motion information of the PU encompassing spatial candidate source position 926.

Fig. 15A-15D are conceptual diagrams illustrating spatial candidate source locations associated with PUs of an NxN partitioned CU 950. PU952, 954, 956, and 958 belong to CU 950. Fig. 15A is a conceptual diagram illustrating example spatial candidate source locations associated with PU 952. As illustrated in the example of fig. 15A, the video coder may generate spatial motion candidates for PU952 based on the motion information of PUs covering spatial candidate source locations 960, 962, 964, 966, and 968. None of the spatial candidate source locations 960, 962, 964, 966, or 968 is located within the CU 950. Thus, the video coder is not required to "move" any of the spatial candidate source locations associated with PU952 to generate motion candidates for PU 952.

Fig. 15B is a conceptual diagram illustrating example spatial candidate source locations associated with PU 954. As illustrated in the example of fig. 15B, the video coder may generate spatial motion candidates for PU954 based on motion information of PUs covering spatial candidate source locations 980, 982, 984, 986, and 988. The spatial candidate source locations 980, 982, and 984 are located outside the CU 950. Position 990 is spatially to the left of PU 954. Position 992 is spatially to the lower left of PU 954. However, locations 990 and 992 are within CU 950. Thus, instead of generating spatial motion candidates based on motion information for PUs that encompass positions 990 and 992 (i.e., PUs 952 and 956), the video coder may generate spatial motion candidates for PU954 based on motion information for PUs that encompass corresponding positions outside of CU950 (i.e., spatial candidate source positions 986 and 988). The spatial candidate source locations 986 and 988 are outside the PU 950.

Fig. 15C is a conceptual diagram illustrating an example spatial candidate source location associated with PU 956. As illustrated in the example of fig. 15C, the video coder may generate spatial motion candidates for PU956 based on the motion information of PUs that encompass the spatial candidate source locations 1000, 1002, 1004, 1006, and 1008. The spatial candidate source locations 1000, 1002, 1004, 1006, and 1008 are locations outside of CU 950. Location 1010 is spatially above PU 956. Location 1012 is spatially above and to the right of PU 956. However, locations 1010 and 1012 are within CU 950. Thus, instead of generating spatial motion candidates based on motion information for PUs that encompass positions 990 and 992 (i.e., PUs 952 and 954), the video coder may generate spatial motion candidates for PU954 based on motion information for PUs that encompass corresponding positions outside of CU950 (i.e., spatial candidate source locations 1000 and 1002).

Fig. 15D is a conceptual diagram illustrating example spatial candidate source locations associated with PU 958. As illustrated in the example of fig. 15D, the video coder may generate spatial motion candidates based on the motion information of PUs that encompass spatial candidate source locations 1020, 1022, 1024, 1026, and 1028. Spatial candidate source locations 1020, 1022, 1024, 1026, and 1028 are locations outside CU 950. Location 1030 is spatially above PU 956. Location 1032 is spatially above and to the left of PU 956. Position 1034 is spatially to the left of PU 958. However, locations 1030, 1032, and 1034 are within CU 950. Thus, instead of generating spatial motion candidates based on motion information for PUs that encompass positions 1030, 1032, and 1034 (i.e., PUs 954, 952, and 956), the video coder may generate spatial motion candidates for PU954 based on motion information for PUs that encompass corresponding positions outside of CU950 (i.e., spatial candidate source positions 1020, 1028, and 1026).

Fig. 14A, 14B, and 15A-15D show a CU partitioned according to Nx2N, 2NxN, and NxN partitioning modes. However, similar concepts may be applied with respect to other segmentation modes.

In one or more examples, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium and executed by a hardware-based processing unit. Computer-readable media may include computer-readable storage media corresponding to tangible media, such as data storage media, or communication media including any medium that facilitates transfer of a computer program from one place to another, such as according to a communication protocol. In this manner, a computer-readable medium may generally correspond to (1) a tangible computer-readable storage medium that is not transitory, or (2) a communication medium such as a signal or carrier wave. A data storage medium may be any available medium that can be accessed by one or more computers or one or more processors to retrieve instructions, code and/or data structures for implementing the techniques described in this disclosure. The computer program product may include a computer-readable medium.

By way of example, and not limitation, such computer-readable storage media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, any connection is properly termed a computer-readable medium. For example, if the instructions are transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, Digital Subscriber Line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. It should be understood, however, that computer-readable storage media and data storage media do not include connections, carrier waves, signals, or other transitory media, but are instead directed to non-transitory, tangible storage media. Disk and disc, as used herein, includes Compact Disc (CD), laser disc, optical disc, Digital Versatile Disc (DVD), floppy disk and blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.

The instructions may be executed by one or more processors, such as one or more Digital Signal Processors (DSPs), general purpose microprocessors, an Application Specific Integrated Circuits (ASICs), field programmable logic arrays (FPGAs), or other equivalent integrated or discrete logic circuitry. Thus, the term "processor," as used herein may refer to any of the foregoing structure or any other structure suitable for implementation of the techniques described herein. In addition, in some aspects, the functionality described herein may be provided within dedicated hardware and/or software modules configured for encoding and decoding, or incorporated in a combined codec. Also, the techniques may be fully implemented in one or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide variety of devices or apparatuses, including a wireless handset, an Integrated Circuit (IC), or a collection of ICs (e.g., a chipset). Various components, modules, or units are described in this disclosure to emphasize functional aspects of devices configured to perform the disclosed techniques, but do not necessarily require realization by different hardware units. Rather, as noted above, the various units may be combined in a codec hardware unit or provided by a collection of interoperating hardware units (including one or more processors as noted above) in conjunction with suitable software and/or firmware.

Various examples have been described. These and other examples are within the scope of the following claims.

Claims (39)

1. A method for coding video data, the method comprising:

for each PU of a plurality of Prediction Units (PUs) belonging to a current Coding Unit (CU), generating a candidate list for the PU such that each candidate in the candidate list generated based on motion information of at least one other PU is generated without using motion information of any other PU belonging to the current CU; and

for each PU belonging to the current CU, generating a predictive video block for the PU based on a reference block indicated by motion information of the PU, the motion information of the PU being determinable based on a motion vector indicated by a selected candidate in the candidate list for the PU.

2. The method of claim 1, wherein generating the candidate lists comprises generating the candidate lists for two or more of the PUs in parallel.

3. The method of claim 1, wherein generating the candidate list comprises generating a merge candidate list shared by all of the PUs of the current CU.

4. The method of claim 3, wherein generating the merge candidate list comprises generating the merge candidate list based on motion information of PUs that are outside the current CU.

5. The method of claim 4, wherein the current CU is partitioned into the plurality of PUs according to a selected partitioning mode other than a 2Nx2N partitioning mode, and the motion information for each of the PUs is determinable based on motion information indicated by a selected candidate in the merge candidate list, wherein the merge candidate list is the same as a candidate list that would be generated if the current CU had been partitioned according to the 2Nx2N partitioning mode.

6. The method of claim 1, wherein generating the candidate list comprises:

generating a temporal candidate based on motion information of a collocated PU in a reference frame indicated by a default reference picture index; and

include the temporal candidate in the candidate list of a current PU, the current PU being one of the PUs belonging to the current CU.

7. The method of claim 1, wherein generating the candidate list comprises generating each temporal candidate in the candidate list based on motion information of a PU in a reference picture indicated by a reference picture index of a PU that covers a location outside the current CU.

8. The method of claim 7, wherein generating the candidate list comprises:

in response to determining that a reference index source location associated with a current PU is within the current CU, identifying a corresponding location that is outside of the current CU, the current PU being one of the PUs belonging to the current CU;

generating temporal candidates based on motion information of collocated PUs in a reference picture indicated by PUs covering the corresponding location outside the current CU; and

including the temporal candidate in the candidate list for the current CU.

9. The method of claim 1, wherein generating the candidate list comprises:

in response to determining that a reference index source PU is not available, searching for available PUs that spatially neighbor the current CU, the reference index source PU being a PU that covers a reference index source location associated with a current PU, the current PU being one of the PUs belonging to the current CU;

generating temporal candidates based on motion information of collocated PUs in reference pictures indicated by reference picture indices of the available PUs; and

including the temporal candidate in the candidate list for the current CU.

10. The method of claim 1, wherein generating the candidate list comprises:

generating spatial candidates based on motion information of PUs that are spatially neighboring a current PU and that are outside the current CU, the current PU being one of the PUs belonging to the current CU; and

including the spatial candidate in the candidate list for the current PU.

11. The method of claim 1, wherein the first and second light sources are selected from the group consisting of,

wherein the set of spatial candidate source locations includes a first spatial candidate source location below and to the left of a current PU, a second spatial candidate source location to the left of the current PU, a third spatial candidate source location above and to the left of the current PU, a fourth spatial candidate source location above the current PU and a fifth spatial candidate source location above and to the right of the current PU, the current PU being one of the PUs belonging to the current CU, and

wherein generating the candidate list comprises:

replacing any of the spatial candidate source locations within the current CU with corresponding spatial candidate source locations outside of the current CU;

generating spatial candidates based on motion information of PUs that encompass the spatial candidate source locations; and

including the spatial candidate in the candidate list for the current PU.

12. The method of claim 1, wherein the first and second light sources are selected from the group consisting of,

wherein coding the video data comprises encoding the video data; and

wherein the method further comprises outputting a candidate index indicating a position of the selected candidate in the candidate list.

13. The method of claim 12, wherein the method further comprises:

generating a motion vector for a current PU, the current PU being one of the PUs belonging to the current CU; and

outputting a motion vector difference, MVD, for a current PU, the MVD for the current PU indicating a difference between the motion vector for the current PU and a motion vector indicated by the selected candidate for the current PU.

14. The method of claim 1, wherein the first and second light sources are selected from the group consisting of,

wherein coding the video data comprises decoding the video data; and

wherein the method further comprises generating a reconstructed video block for the current CU based on the predictive video block of the PU.

15. The method of claim 14, further comprising identifying the reference block for a current PU based on a motion vector indicated by the selected candidate in the candidate list for the current PU.

16. The method of claim 14, wherein the method further comprises:

receiving an MVD for a current PU, the current PU being one of the PUs belonging to the current CU;

determining a motion vector for the current PU based on a motion vector indicated by the selected candidate in the candidate list for the current PU; and

identifying the reference block of the current PU based on the motion vector of the current PU.

17. A video coding device comprising one or more processors configured to:

for each PU of a plurality of Prediction Units (PUs) belonging to a current Coding Unit (CU), generating a candidate list for the PU such that each candidate in the candidate list generated based on motion information of at least one other PU is generated without using motion information of any of the PUs belonging to the current CU; and

for each PU belonging to the current CU, generating a predictive video block for the PU based on a reference block indicated by motion information of the PU, the motion information of the PU being determinable based on a motion vector indicated by a selected candidate in the candidate list for the PU.

18. The video coding device of claim 17, wherein the one or more processors are configured to generate the candidate lists for two or more of the PUs in parallel.

19. The video coding device of claim 17, wherein the one or more processors are configured to generate a merge candidate list that is shared by all of the PUs of the current CU.

20. The video coding device of claim 19, wherein the one or more processors are configured to generate the merge candidate list based on motion information of PUs that are outside the current CU.

21. The video coding device of claim 20, wherein the current CU is partitioned into the plurality of PUs according to a selected partitioning mode other than a 2Nx2N partitioning mode, and the motion information for each of the PUs is determinable based on motion information indicated by a selected candidate in the merge candidate list, wherein the merge candidate list is the same as a candidate list that would be generated if the current CU was partitioned according to the 2Nx2N partitioning mode.

22. The video coding device of claim 17, wherein the one or more processors are configured to:

generating a temporal candidate based on motion information of a collocated PU in a reference frame indicated by a default reference picture index; and

include the temporal candidate in the candidate list of a current PU, the current PU being one of the PUs belonging to the current CU.

23. The video coding device of claim 17, wherein the one or more processors are configured to generate each temporal candidate in the candidate list based on motion information of a PU in a reference picture indicated by a reference picture index of a PU that covers a location outside of the current CU.

24. The video coding device of claim 23, wherein the one or more processors are configured to:

in response to determining that a reference index source location associated with a current PU is within the current CU, identifying a corresponding location that is outside of the current CU, the current PU being one of the PUs belonging to the current CU;

generating temporal candidates based on motion information of collocated PUs in a reference picture indicated by PUs covering the corresponding location outside the current CU; and

including the temporal candidate in the candidate list for the current CU.

25. The video coding device of claim 17, wherein the one or more processors are configured to:

in response to determining that a reference index source PU is not available, searching for available PUs that spatially neighbor the current CU, the reference index source PU being a PU that covers a reference index source location associated with a current PU, the current PU being one of the PUs belonging to the current CU;

generating temporal candidates based on motion information of collocated PUs in reference pictures indicated by reference picture indices of the available PUs; and

including the temporal candidate in the candidate list for the current CU.

26. The video coding device of claim 17, wherein the one or more processors are configured to:

generating spatial candidates based on motion information of PUs that are spatially neighboring a current PU and that are outside the current CU, the current PU being one of the PUs belonging to the current CU; and

including the spatial candidate in the candidate list for the current PU.

27. The video coding device of claim 17,

wherein the set of spatial candidate source locations includes a first spatial candidate source location below and to the left of a current PU, a second spatial candidate source location to the left of the current PU, a third spatial candidate source location above and to the left of the current PU, a fourth spatial candidate source location above the current PU and a fifth spatial candidate source location above and to the right of the current PU, the current PU being one of the PUs belonging to the current CU, and

wherein the one or more processors are configured to:

replacing any of the spatial candidate source locations within the current CU with corresponding spatial candidate source locations outside of the current CU;

generating spatial candidates based on motion information of PUs that encompass the spatial candidate source locations; and

including the spatial candidate in the candidate list for the current PU.

28. The video coding device of claim 17, wherein the video coding device encodes video data and is configured to output a candidate index indicating a position of the selected candidate in the candidate list.

29. The video coding device of claim 28, wherein the one or more processors are configured to:

generating a motion vector for a current PU, the current PU being one of the PUs belonging to the current CU; and

outputting a motion vector difference, MVD, for a current PU, the MVD for the current PU indicating a difference between the motion vector for the current PU and a motion vector indicated by the selected candidate for the current PU.

30. The video coding device of claim 17, wherein the video coding device decodes video data and is configured to generate a reconstructed video block for the current CU based on the predictive video block of the PU.

31. The video coding device of claim 30, wherein the one or more processors are configured to identify the reference block for a current PU based on a motion vector indicated by the selected candidate in the candidate list for the current PU.

32. The video coding device of claim 30, wherein the one or more processors are further configured to:

receiving an MVD for a current PU, the current PU being one of the PUs belonging to the current CU;

determining a motion vector for the current PU based on a motion vector indicated by the selected candidate in the candidate list for the current PU; and

identifying the reference block of the current PU based on the motion vector of the current PU.

33. The video coding device of claim 17, wherein the video coding device is a mobile computing device.

34. A video coding device, comprising:

means for generating, for each PU of a plurality of Prediction Units (PUs) belonging to a current Coding Unit (CU), a candidate list for the PU such that each candidate in the candidate list generated based on motion information of at least one other PU is generated without using motion information of any of the PUs belonging to the current CU; and

means for generating, for each PU belonging to the current CU, a predictive video block for the PU based on a reference block indicated by motion information of the PU, the motion information of the PU determinable based on a motion vector indicated by a selected candidate in the candidate list for the PU.

35. The video coding device of claim 34, wherein the one or more processors are configured to generate the candidate lists for two or more of the PUs in parallel.

36. The video coding device of claim 34, wherein the one or more processors are configured to generate a merge candidate list that is shared by all of the PUs of the current CU.

37. A computer program product comprising one or more computer-readable storage media storing instructions that, when executed, configure one or more processors to:

for each PU of a plurality of Prediction Units (PUs) belonging to a current Coding Unit (CU), generating a candidate list for the PU such that each candidate in the candidate list generated based on motion information of at least one other PU is generated without using motion information of any of the PUs belonging to the current CU; and

for each PU belonging to the current CU, generating a predictive video block for the PU based on a reference block indicated by motion information of the PU, the motion information of the PU being determinable based on a motion vector indicated by a selected candidate in the candidate list for the PU.

38. The computer program product of claim 37, wherein the instructions configure the one or more processors to generate the candidate lists for two or more of the PUs in parallel.

39. The computer program product of claim 37, wherein the instructions configure the one or more processors to generate a merge candidate list that is shared by all of the PUs of the current CU.