JP2006180036A - Video encoding transmission control apparatus and video encoding transmission control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To encode a moving picture that can suppress a peak bit rate from the outside of an encoding device, can be realized with a very simple configuration and method, and can output encoded data at a bit rate conforming to a standard To provide a transmission control device and a moving image encoding transmission control method.
A transmission bit rate monitoring unit for monitoring an output bit rate output from a transmission buffer memory, and a transmission buffer memory when the output bit rate exceeds a certain value as monitored by the transmission bit rate monitoring unit. The output bit rate can be lowered by providing the switch for limiting the data output from the output terminal 22, and as a result, the VBV buffer underflow can be avoided. Therefore, the peak bit rate can be suppressed by simple control from the outside of the encoding block 20, and encoded data can be output at a bit rate compliant with the standard.
[Selection] Figure 1

Description

  The present invention relates to a moving image encoding transmission control apparatus and a moving image encoding transmission control method for performing compression encoding on an input moving image and transmitting it to a line or a recording medium, and more particularly to a maximum bit rate (peak bit) of compressed data. The present invention relates to a moving image coding / transmission control apparatus and a moving image coding / transmission control method for controlling a rate to a certain level or less.

  In recent years, a moving image encoding technique such as MPEG-4 has been used in various devices such as mobile terminals, movie cameras, and digital cameras. MPEG-4 is an ISO recommendation, and is initially used mainly for moving picture compression at a low bit rate, for example, a TV phone in a third generation mobile phone. However, the technological progress in recent years has been remarkable, and what can be recorded on the storage media in QVGA (Quater VGA: 320 × 240) size has become the mainstream, and in the near future, equipment that supports compression at larger sizes and bit rates will be the mainstream. It is expected that

  Various problems such as processing speed and image quality occur in handling such compressed data. Especially in the case of high bit rate data, problems such as the transfer speed of storage media, recording capacity, transmission capacity of lines and networks become severe, and it is necessary to pay careful technical attention especially when the bit rate is exceeded. is there.

  For example, in the recommendation MPEG-4 (ISO / IEC JTC1 / SC29 / WG11 N3056), the bit rate variation is limited by the VBV (Video Buffering Verifier) buffer model, which is a virtual reception buffer model connected to the encoder output. Yes.

  Referring to FIG. 4, data always flows into the buffer at a constant bit rate, and data is instantaneously removed from the buffer by the number of bits of VOP (Video Object Plane) at the decoding time (Tn). When the amount of data in the VBV buffer becomes 0, it is called underflow. When there is a large VOP (particularly continuously) that causes the VBV buffer to fail, that is, the bit rate exceeds the allowable range. means.

  Conversely, the case where the VBV buffer size is exceeded is called overflow, and corresponds to the case where VOPs with almost no code amount continue. Therefore, it is necessary to prevent the overflow or underflow of the VBV buffer. In particular, the VBV buffer underflow means that the bit rate is exceeded. Therefore, even when the variable bit rate control is used instead of the fixed bit rate, the transfer rate of the recording medium and the line transmission bit rate are within the allowable range. Must be avoided.

  As a technique for avoiding VBV buffer underflow, for example, the stream data occupation amount of the transmission buffer memory is monitored, and in the case of VBV buffer underflow (exceeding bit rate), frame skip (generally called frame dropping) However, in this specification, a technique for performing frame skip) is generally known (see, for example, Patent Document 1).

  FIG. 5 shows the configuration of a conventional encoding device (frame drop control circuit) that performs general frame skipping. The encoding unit 61 encodes input data from the outside, and stores the stream data as the encoding result in the transmission buffer memory 62. In the encoded bit rate monitoring unit 63, the bit rate of the encoded stream data is checked in real time by monitoring the encoded bit rate from the data on the transmission buffer memory 62. The frame skip control unit 64 performs frame skip.

This operation will be described with reference to FIG. 6. In the case where the VBV buffer underflows between times T3 and T4 (FIG. 6A), at time T3 as shown in FIG. 6B. Underflow of the VBV buffer is avoided by skipping frames.
JP 2000-209584 A

  Thus, in order to prevent the VBV buffer underflow, the fixed bit rate control by the frame skip control as in the conventional frame drop control circuit is very effective. However, with such a method, it is possible to guarantee that the bit rate is maintained, but since frame skip frequently occurs, it becomes a rattling impression especially in a scene with a large movement, and there is also a problem in image quality. In the conventional frame drop control circuit, control is performed so that the frame skip intervals are equalized, but a reduction in the frame rate is inevitable. Therefore, variable bit rate (VBR) control is often used instead of bit rate control by frame skip in movie applications where recording with high image quality is desired. When variable bit rate control is used, since it is possible to perform encoding by assigning an appropriate code amount for each frame (VOP), it is easy to fix the frame rate by eliminating frame skipping, and the image quality is very good. . For example, almost no information is required for a frame with little motion, but the surplus can be allocated to a frame with intense motion or a complex image.

  However, even when variable bit rate control is performed with the aim of improving image quality, it is necessary to suppress the bit rate by the VBV buffer model in the standard, but in reality, stream data whose peak bit rate exceeds the specification There are actually many encoding devices to output.

  In addition, it is technically difficult to perfectly maintain the bit rate regardless of what input is encoded with variable bit rate control. For example, images such as white noise have the lowest coding efficiency, and quantum quantization. The control of the coding parameter has almost no effect on the control of the code amount, and when such an input is continuous, the peak bit rate jumps at a stretch unless any countermeasure is taken.

  In normal natural images, the above-mentioned phenomenon does not become a serious problem, but if an artificial image or the like is intentionally input, there is a case where the peak bit rate is greatly exceeded due to underflow of the VBV buffer. . In many cases, such a problem is discovered later in the commercialization phase, and in such a case, there is a problem that it is very expensive to fundamentally improve the main body of the encoding apparatus.

  The present invention has been made to solve such a conventional problem, and can suppress the peak bit rate from the outside of the encoding apparatus and can be realized with a very simple configuration and method. A moving image encoding transmission control apparatus and a moving image encoding transmission control method are provided.

  The moving image encoding transmission control apparatus according to the present invention includes an encoding unit that encodes an input image, a buffer memory that temporarily stores the encoded data, and an amount of data that occupies the buffer memory. Buffer occupancy monitoring means for monitoring the data, coding skip control means for causing the encoding means to skip encoding processing based on the data occupancy of the buffer memory monitored by the buffer occupancy monitoring means, and the buffer Transmission bit rate monitoring means for monitoring the output bit rate output from the memory, and limiting the data output from the buffer memory when the output bit rate exceeds a certain value by monitoring the transmission bit rate monitoring means And an output limiting means.

  With this configuration, the output bit rate can be lowered by monitoring the output bit rate from the outside of the buffer memory and restricting the output, and as a result, the VBV buffer underflow can be avoided. Therefore, the peak bit rate can be suppressed by simple control from the outside of the basic encoding processing portion, and encoded data can be output at a bit rate compliant with the standard.

  Also, the moving image coding transmission control apparatus of the present invention has a configuration characterized in that the coding means codes the input image by variable bit rate control based on a fixed frame rate.

  With this configuration, encoding can be performed by allocating an appropriate code amount for each frame, so that the peak bit rate is suppressed, the system is not broken down, and the occurrence of frame skip is suppressed to make the frame rate uniform. It is easy to improve the image quality.

  Furthermore, in the moving image coding transmission control apparatus of the present invention, the output restriction means provides an output restriction value and a restriction release value, and when the output bit rate output from the buffer memory exceeds the output restriction value, The data output from the buffer memory is limited, and when the output bit rate becomes less than the limit cancellation value, the limitation on the data output from the buffer memory is canceled. .

  With this configuration, the data output from the buffer memory is limited and released by different values depending on the output limit value and the limit release value, so that data output can be performed within a desired bit rate range, and output limit and The frequency of releasing the restriction can be reduced, and the load on the apparatus can be suppressed.

  Furthermore, the mobile communication system of the present invention has a configuration characterized by including any of the above-described moving image coding transmission control apparatuses.

  With this configuration, it is possible to achieve the same operational effects as those of the moving picture coding transmission control apparatus described above in the mobile communication system.

  Furthermore, the moving image encoding transmission control method of the present invention includes an encoding step for encoding an input image, a data storage step for temporarily storing the encoded encoded data in a buffer memory, and the buffer memory. A buffer occupation amount monitoring step for monitoring the amount of occupied data, an encoding skip control step for skipping the encoding process based on the monitored data occupation amount of the buffer memory, and output from the buffer memory A transmission bit rate monitoring step for monitoring an output bit rate; and an output limiting step for limiting data output from the buffer memory when the output bit rate exceeds a certain value by the monitoring. It has the structure.

  With this configuration, the output bit rate can be lowered by monitoring the output bit rate from the outside of the buffer memory and restricting the output, and as a result, the VBV buffer underflow can be avoided. Therefore, the peak bit rate can be suppressed by simple control from the outside of the basic encoding processing portion, and encoded data can be output at a bit rate compliant with the standard.

  Furthermore, the moving image encoding transmission control program of the present invention includes an encoding step for encoding an input image, a data storage step for temporarily storing the encoded encoded data in a buffer memory, and the buffer memory. A buffer occupation amount monitoring step for monitoring the amount of occupied data, an encoding skip control step for skipping the encoding process based on the monitored data occupation amount of the buffer memory, and output from the buffer memory A transmission bit rate monitoring step for monitoring an output bit rate; and an output limiting step for limiting data output from the buffer memory when the output bit rate exceeds a certain value by the monitoring. It has the structure.

  With this configuration, the output bit rate can be lowered by monitoring the output bit rate from the outside of the buffer memory and restricting the output, and as a result, the VBV buffer underflow can be avoided. Therefore, the peak bit rate can be suppressed by simple control from the outside of the basic encoding processing portion, and encoded data can be output at a bit rate compliant with the standard.

  The present invention relates to a transmission bit rate monitoring unit that monitors an output bit rate output from a buffer memory, and an output limiting unit that limits data output from the buffer memory when the output bit rate exceeds a certain value. By providing this, the output bit rate can be monitored from the outside of the buffer memory, the output can be limited, and the output bit rate can be lowered, and as a result, the VBV buffer underflow can be avoided. Therefore, it is possible to suppress the peak bit rate by a simple control from the outside of the basic encoding process part, and the moving image encoded transmission has the effect that the encoded data can be output at the bit rate conforming to the standard. A control device can be provided.

  Hereinafter, a moving image encoding transmission control apparatus according to an embodiment of the present invention will be described with reference to the drawings.

  First, a configuration diagram of a moving image coding transmission control apparatus according to an embodiment of the present invention will be described with reference to FIG.

  As shown in FIG. 1, the moving picture coding / transmission control apparatus 10 according to the present invention includes a coding block 20 that performs coding using frame skip according to the data occupancy, and an output bit rate output from the coding block 20. The transmission bit rate monitoring unit 31 for monitoring the data and the switch 32 for stopping the data output from the encoding block 20 when the output bit rate output from the encoding block 20 exceeds a certain value. The switch 32 constitutes output limiting means of the present invention. The encoding block 20 includes an encoding unit 21 that encodes an input image, a transmission buffer memory 22 that temporarily stores encoded data, and a buffer occupation amount that monitors the amount of data that occupies the transmission buffer memory 22. Based on the data occupancy of the monitoring unit 23 and the transmission buffer memory 22, the frame skip control unit 24 that causes the encoding unit 21 to skip the frame encoding process is provided.

  The encoding unit 21 encodes an input image, particularly a moving image in the present embodiment, by a method such as the recommended MPEG-4, for example. H.263 and H.264. H.264, H.C. A system such as H.261, MPEG-1, or MPEG-2 may be used. The encoding unit 21 may be considered to follow conventional encoding means, and may have a configuration in which an input device such as a camera is added to the previous stage or a configuration in which an input image buffer is added.

  The transmission buffer memory 22 is used for temporarily storing output data of the encoding unit 21, that is, bit stream data, and serves as a buffer for waiting for output to a line or a recording medium. For example, if the output cannot be performed due to heavy traffic, data is stored in the transmission buffer memory 22. A specific configuration of the transmission buffer memory 22 may be a dual port memory having an input terminal and an output terminal, or may be controlled to switch input and output each time in a single-port multi-bank configuration. A ring buffer having a read and write pointer or a buffer having a FIFO structure may be used. Further, in this embodiment, the bit rate control is based on the fixed frame rate and variable bit rate control that does not cause frame skip except for physically preventing the overflow of the transmission buffer memory 22, thereby improving the image quality. Use what you want. Since the variable bit rate is assumed, the data stored in the transmission buffer memory 22 may be immediately output to the transmission destination. The transmission buffer memory 22 does not have to be the same as the VBV buffer size, and is different from the VBV buffer. For example, it is often fixedly assigned to the corresponding maximum VBV buffer size for convenience of implementation.

  The buffer occupancy monitoring unit 23 monitors the buffer occupancy in order to prevent the transmission buffer memory 22 from physically overflowing. For example, it is provided assuming a case where output from the transmission buffer memory 22 is impossible, for example, when line traffic is extremely busy.

  The frame skip control unit 24 prevents a new inflow to the transmission buffer memory 22 by skipping the encoding process when the buffer occupancy monitoring unit 23 determines that the transmission buffer memory 22 is close to overflow. Prevent overflow. That is, frame skip control is performed on the encoding unit 21 in the case where the overflow is close. Note that a certain threshold value may be provided as a condition for performing this frame skip, and the threshold value may be freely adjusted by the system.

  The transmission bit rate monitoring unit 31 monitors the output bit rate from the transmission buffer memory 22. By stopping the output from the transmission buffer memory 22 when the output bit rate exceeds the allowable range, only the inflow from the encoding unit 21 enters the transmission buffer memory 22, and the transmission buffer memory 22 is in a nearly full state. As a result, the frame is skipped by the action of the buffer occupation amount monitoring unit 23 and the frame skip control unit 24. As a result, the output bit rate can be suppressed, and overflow of the transmission buffer memory 22 can be avoided. As a condition for stopping output from the transmission buffer memory 22, for example, a threshold value may be provided, and a means for stopping when the output bit rate exceeds the threshold value may be provided. A means for freely changing the threshold value may be provided. When the output bit rate decreases, the output from the transmission buffer memory 22 is resumed. Note that the condition for restarting, that is, the threshold value for restarting may be set separately from the threshold value for stopping, and the threshold value can be freely changed by the system in the same manner as the output stop. Means may be provided. Here, the threshold value for restart is the limit release value of the present invention, and the threshold value for stop is the output limit value. Further, regarding the monitoring portion of the actual output bit rate, a terminal may be provided on the output from the transmission buffer memory 22 and observed.

  The switch 32 is a mechanism that actually stops the output from the transmission buffer memory 22. A means that can switch between connection and non-connection as in the present embodiment may be used, or a means that stops outputting actual data while being physically connected may be used. A means for stopping the operation of reading data on the memory in software may be used.

  The encoding process and frame skip processing operation in the encoding block 20 of the moving picture encoding transmission control apparatus 10 configured as described above will be described with reference to a flowchart shown in FIG.

  First, the buffer occupation amount monitoring unit 23 checks the amount of data occupied in the transmission buffer memory 22 (S11). Next, the frame skip control unit 24 determines whether or not it is frame skip, that is, whether or not encoding is possible (S12). When frame skipping is performed, the transmission buffer memory 22 is almost full, and the frame skip control unit 24 controls the presence or absence of frame skipping. When frame skip is not performed, that is, when encoding is performed, encoding processing is performed by the encoding unit 21 (S13). When the encoding process is completed, the bit stream data is stored in the transmission buffer memory 22 (S14). Here, processing for one frame (1 VOP) is completed, and processing for the next frame is performed.

  Subsequently, the buffer occupancy monitoring unit 23 measures the amount of data currently remaining in the transmission buffer memory 22 until the previous frame processing (S11), and determines whether or not there is sufficient space in the transmission buffer memory 22 (S11). S12). If there is enough free space, it is determined that encoding is possible, and encoding processing is performed (S13). As an example of a criterion for determining whether or not encoding is possible, whether or not the buffer free capacity is the maximum code amount of one frame (1 VOP) may be applied. In addition, an appropriate threshold value may be set as a determination criterion within a range that does not physically overflow.

  On the other hand, if it is determined that the encoding is impossible, the process waits until the transmission buffer memory 22 becomes empty (S15). If it is determined that the encoding can be resumed, the process proceeds to the encoding process (S13). Thereafter, the processing is repeated in the same manner as described above.

  The input of data to the transmission buffer memory 22 has been described so far, but it is assumed that data is output from the transmission buffer memory 22 and transmitted to, for example, a line, a network, or a recording medium. The transmission buffer memory 22 may be configured so that the input and the output can be performed at the same time. Here, the description will be made assuming that both are performed asynchronously.

  Data is output from the transmission buffer memory 22 in accordance with the output destination of the buffer, that is, the status of the output connection destination. For example, when the line traffic is congested, the data rate to be output may be lowered. Conversely, when the line is available, the data in the transmission buffer memory 22 may be output at a stretch. In order to reduce the possibility of frame skipping as much as possible, it is preferable to output the data in the buffer within a short time.

  Here, the transmission bit rate monitoring unit 31 constantly monitors the output bit rate from the transmission buffer memory 22. When the bit rate becomes higher than a certain level, the switch 32 is disconnected from the line and the output from the transmission buffer memory 22 is stopped. By this operation, data continues to flow into the transmission buffer memory 22 and the buffer occupation amount increases. Therefore, frame skip is executed in accordance with the conditions shown in the buffer occupancy check processing (S11, S12). Since the output from the transmission buffer memory 22 is stopped, it means that the output bit rate is lowered. Even if output is stopped, the transmission buffer memory 22 does not overflow due to frame skipping.

  If the transmission bit rate monitoring unit 31 determines that the rate has fallen below a certain level, the switch 32 connects the line and the transmission buffer memory 22 again to output data from the transmission buffer memory 22. Since the buffer occupancy decreases, the encoding process is automatically restarted. The determination criterion for stopping and restarting output from the transmission buffer memory 22 may be adaptively changed according to the situation.

  A bit rate control image on the transmission line will be described with reference to FIG. FIG. 3A shows a case where peak bit rate control is not performed. That is, this is the case of an encoding device that cannot avoid a VBV buffer underflow that does not conform to the standard. The horizontal axis represents the transition of time, and the vertical axis represents the bit rate. The bit rate changes with the average bit rate as the center, but there is a section where the maximum allowable rate is exceeded. As a possibility that such a phenomenon exists, it is conceivable that an image having a very poor encoding efficiency such as a sudden scene change or white noise is input. If the maximum allowable rate is exceeded in this way, there is a possibility that the system will break down, such as the line capacity being over or the writing speed of the recording medium not being in time.

  FIG. 3B shows a case where bit rate monitoring as shown in the present embodiment is applied to an encoding apparatus that may break the system. Since the output from the transmission buffer memory 22 is stopped when the threshold value is exceeded, the bit rate can be lowered. Therefore, the system will not fail without exceeding the maximum allowable rate.

  As described above, according to the present embodiment, by using the physical overflow prevention mechanism of the transmission buffer memory 22, here, the buffer occupancy monitoring unit 23 and the frame skip control unit 24, the coding block 20 By monitoring the output bit rate from the outside and stopping the output, the peak value of the output bit rate can be suppressed without causing physical memory failure as a result, and this does not have a VBV buffer underflow prevention mechanism. This embodiment is also equivalent to avoiding VBV buffer underflow.

  The moving image coding transmission control apparatus 10 according to the embodiment of the present invention is capable of setting the peak bit rate by simple control from the outside even in an encoding apparatus that does not comply with the standard as compared with the conventional technique. It is possible to suppress this, and it has an excellent effect in that the system can operate in compliance with the standard.

  In the present embodiment, the means after the switch 32 is not specified, but a configuration in which appropriate devices and apparatuses such as a line including a mobile communication line, a network, and a memory device such as a recording medium are connected may be used. In this embodiment, the output bit rate from the transmission buffer memory 22 is monitored, and the output from the transmission buffer memory 22 is stopped when the bit rate exceeds a certain level. However, in such a case, there is no problem even if it is configured as means for adjusting so as to reduce the output from the transmission buffer memory 22, and the effect according to the present invention can be obtained.

  Further, the present invention can be incorporated as a mobile terminal, for example, and can be realized as a mobile communication system including the mobile terminal device, for example.

  The present invention can also be realized as software, and the present invention can be realized by reading from a recording medium containing the software.

  As described above, the moving image encoding transmission control apparatus according to the present invention can suppress the peak bit rate by simple control from the outside of the basic encoding processing part, and encodes at a bit rate compliant with the standard. The present invention has an effect that data can be output, and is useful as a moving image coding transmission control device that performs compression coding on an input moving image and transmits it to a line, a recording medium, or the like.

The block diagram which shows the structure of the moving image encoding transmission control apparatus in embodiment of this invention The flowchart which shows the encoding process and frame skip process operation in embodiment of this invention (A) Graph showing transition of bit rate on transmission line when peak bit rate control is not performed (b) On transmission line when bit rate monitoring of this embodiment is applied and peak bit rate control is performed Graph showing changes in bit rate Graph showing the transition of the amount of data in the buffer of the conventional VBV buffer model Block diagram showing a conventional encoding apparatus for performing frame skipping (A) Graph showing transition of data amount in VBV buffer when conventional VBV buffer underflow occurs (b) Graph showing transition of data amount in VBV buffer when conventional VBV buffer underflow is avoided

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Moving image encoding transmission control apparatus 20 Encoding block 21 Encoding part 22 Transmission buffer memory 23 Buffer occupation amount monitoring part 24 Frame skip control part 31 Transmission bit rate monitoring part 32 Switch (output restriction means)
61 Encoding unit 62 Transmission buffer memory 63 Encoding bit rate monitoring unit 64 Frame skip control unit

Claims (6)

Encoding means for encoding an input image;
A buffer memory for temporarily storing the encoded encoded data;
Buffer occupancy monitoring means for monitoring the amount of data occupying the buffer memory;
Encoding skip control means for causing the encoding means to skip encoding processing based on the data occupation amount of the buffer memory monitored by the buffer occupation amount monitoring means;
Transmission bit rate monitoring means for monitoring the output bit rate output from the buffer memory;
A moving picture encoding transmission control apparatus comprising: output limiting means for limiting data output from the buffer memory when the output bit rate exceeds a certain value as monitored by the transmission bit rate monitoring means. . 2. The moving image encoding transmission control apparatus according to claim 1, wherein the encoding unit encodes the input image by variable bit rate control based on a fixed frame rate. The output limiting means provides an output limit value and a limit release value, and limits the data output from the buffer memory when the output bit rate output from the buffer memory exceeds the output limit value, and the output 3. The moving image encoding transmission control apparatus according to claim 1, wherein when the bit rate becomes less than the restriction release value, the restriction on data output from the buffer memory is released. A mobile communication system comprising the moving image encoding transmission control apparatus according to any one of claims 1 to 3. An encoding step for encoding the input image;
A data storage step of temporarily storing the encoded encoded data in a buffer memory;
A buffer occupancy monitoring step for monitoring the amount of data occupying the buffer memory;
An encoding skip control step for skipping the encoding process based on the monitored data occupation amount of the buffer memory;
A transmission bit rate monitoring step of monitoring an output bit rate output from the buffer memory;
A video encoding transmission control method comprising: an output limiting step of limiting data output from the buffer memory when the output bit rate exceeds a certain value by the monitoring. An encoding step for encoding the input image;
A data storage step of temporarily storing the encoded encoded data in a buffer memory;
A buffer occupancy monitoring step for monitoring the amount of data occupying the buffer memory;
An encoding skip control step for skipping the encoding process based on the monitored data occupation amount of the buffer memory;
A transmission bit rate monitoring step of monitoring an output bit rate output from the buffer memory;
A video encoding transmission control program, comprising: an output limiting step for limiting data output from the buffer memory when the output bit rate exceeds a certain value by the monitoring.

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