JP2004180339A - Compressed moving picture re-coding system and compressed moving picture re-coding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize reduction in a process delay during re-coding of a compressed moving picture, and to provide a compressed moving picture re-coding system with higher image quality. <P>SOLUTION: Using either and/or both of a quantization width and a code quantity in an input compressed moving picture stream, a complexity calculation means 101 calculates each complexity for two or more given time period or number of pictures. In addition, a picture group quantization width calculation means 102 outputs one complexity from a plurality of complexities, and a quantization width control means 103 uses a preset average bit rate and the output complexity to calculate a quantization width. Furthermore, using overs or shorts from target number of codes and actual number of codes, a quantization width selector 104 controlling a quantization width per time period calculates a quantization width used for re-coding, and controls the number of codes by inputting the quantization width and the quantization width in the input compressed moving picture stream and outputting a quantization width used for actual re-coding. Thus, the system will perform re-coding with a variable bit rate to output a compressed moving picture stream with modified bit rate. <P>COPYRIGHT: (C)2004,JPO

Description

  The present invention relates to a compressed moving image re-encoding device and a compressed moving image re-encoding method, and in particular, to a compressed moving image re-encoding device and a compressed moving image re-encoding that reduce the amount of code of a compressed moving image serving as an input signal. About the method.

  2. Description of the Related Art Conventionally, a compressed moving image re-encoding device and a compressed moving image re-encoding method are applied to a device or method for transmitting and storing a moving image signal, such as a digital broadcasting system and a service. When transmitting and storing a moving image signal such as in a digital broadcasting system or service, the moving image signal is compression-encoded and transmitted and stored. In recent years, ISO / ICE IS13818-2 (MPEG-2 VIDEO) and the like have been standardized as a compression encoding method for moving image signals, and are used for digital broadcasting systems and services.

  On the other hand, broadcasting stations and homes are expected to have an application that re-encodes a compressed video stream compressed and encoded at a predetermined bit rate as a compressed video stream of a different bit rate, and transmits and stores it. For example, there is a recording function for a digital recording device.

  A compressed moving image stream distributed from a broadcasting station to a home is encoded at a predetermined bit rate. When a viewer records a compressed video stream distributed to a limited storage capacity for a long-time recording or the like, it is necessary to re-encode the compressed video stream at a bit rate lower than the bit rate at the time of distribution. . In this case, it is desirable to suppress image quality degradation during re-encoding. Hereinafter, a conventional technique relating to such a re-encoding process of a compressed moving image stream will be specifically described.

  In the following description, it is assumed that the compressed moving image stream has been compression-encoded according to MPEG-2 VIDEO. Therefore, in the following, an MPEG-2 bit stream is used. In MPEG-2 VIDEO, a picture is divided into blocks composed of a group of a plurality of pixels, and a discrete cosine transform (DCT) is performed on each block, thereby converting a spatial domain signal into a frequency domain signal. Each frequency component obtained by the discrete cosine transform is quantized by a predetermined quantization width, and is variable-length coded by assigning a variable-length code to a quantized transform coefficient, and is output as an MPEG-2 bit stream. The compressed video re-encoding device can be basically realized by decoding an MPEG-2 bit stream as an input signal into a video signal, and re-encoding the decoded video signal. Therefore, the compressed moving picture re-encoding device is configured by a decoder and an encoder connected in series.

  FIG. 12 shows a basic configuration of the decoder. The decoder shown in FIG. 12 includes a variable length decoder 201, an inverse quantizer 202, an inverse discrete cosine transformer 203, an adder 204, a frame memory 205, and a motion compensation predictor 206. You.

  FIG. 13 shows a basic configuration of the encoder. The encoder shown in FIG. 13 includes a subtractor 301, a discrete cosine transformer 302, a quantizer 303, a variable length encoder 304, a code amount control unit 305, an inverse quantizer 306, It comprises an inverse discrete cosine transformer 307, an adder 308, a frame memory 309, and a motion compensation predictor 310.

  FIG. 14 shows a basic configuration of the compressed moving picture re-encoding device. For the sake of explanation, the variable length decoder 201 and the inverse quantizer 202 are referred to as a decoding path unit 41, the quantizer 303 and the variable length encoder 304 are referred to as a coding path unit 43, and the decoding path unit 41 and the coding path The components other than the unit 43 and the code amount control unit 401 are referred to as an error compensating unit 42.

  As described above, since the compressed moving picture re-encoding device shown in FIG. 14 includes the decoder and the encoder connected in series, the decoder shown in FIG. 12 and the encoder shown in FIG. Connected. Further, the compressed moving picture re-encoding device reuses the encoded information decoded by the variable length decoder 201 as an encoding parameter at the time of re-encoding for the purpose of speeding up processing and improving image quality.

  On the other hand, apparatuses for re-encoding a compressed moving image more simply and at lower cost are disclosed in Patent Documents 1 and 2, and the like. FIG. 15 shows a basic configuration of a compressed moving picture re-encoding device disclosed in Patent Document 1. The compressed moving picture re-encoding device shown in FIG. 15 has a configuration in which the error compensating unit 42 shown in FIG. 14 is omitted for simplification of processing, and a decoding path 51, an encoding path 52, and a code amount controller 501 alone. However, when this device is used, image quality is deteriorated due to accumulation of quantization errors due to requantization.

  FIG. 16 shows a basic configuration of a compressed moving picture re-encoding device disclosed in Patent Document 2. The compressed moving picture re-encoding device shown in FIG. 16 simplifies the processing by using an error compensator 62, which is a conversion equivalent to the error compensator 42 of FIG.

  These prior arts disclose the configuration of the compressed moving picture re-encoding device, but do not describe code amount control in the code amount control unit 401. Next, a conventional technique in the code amount control method of the compressed moving image re-encoding device will be described.

  As Conventional Example 1, a method of an MPEG-2 test model (Test Model 5, ISO / ICE JTC1 / SC21 / WG11 / N0400, April 1993), which is a code amount control method of an encoding device, is known. In this method, a fixed bit rate coding method is used in which the amount of code generated by intra-frame coding and inter-frame predictive coding is made to be constant at a certain unit time. As a result, the picture is divided into 16 × 16 pixels in units of macroblocks so that the amount of code generated by the encoding process for each GOP is constant in units of a GOP (Group Of Pictures) which is a set of a plurality of pictures. The code amount is controlled by setting the basic quantization width to be set.

  However, the above-mentioned conventional example 1 is a code amount control method of an encoding device, and the control requires information that is not included in the MPEG-2 bit stream, so that it cannot be directly applied. On the other hand, a code amount control method suitable for a compressed moving picture re-encoding device has been proposed in place of the code amount control method of the above-mentioned conventional example 1. For example, United States Patent 5,657,015 discloses a code amount control method in the compressed video recoding device shown in FIG. 15 as Conventional Example 2.

  In this method, a basic quantization width is set for each macroblock based on an average quantization width of a picture after re-encoding, a target code amount of a picture, and an actual code amount. Next, the activity is calculated using the average quantization width of the picture, the ratio of the quantization width of the macroblock to be coded or the code amount of the picture, and the ratio of the code amount of the macroblock to be coded. The code amount is controlled by adjusting the quantization width.

As Conventional Example 3, United States Patent 5,805,224 is disclosed. In this method, a target code amount of a sub-picture at the time of re-encoding is set based on an input bit rate, an output bit rate, and a code amount of a picture to be coded. Ask for degrees. Next, the complexity is distributed according to the target generated code amount of the sub-picture, and the quantization width of the sub-picture is set. Next, the difference between the target code amount and the actual code amount is reflected in the control, and the quantization amount is adjusted to adjust the code amount. In these conventional examples 2 and 3, the target code amount at the time of re-encoding is set using the code amount of the picture of the input compressed moving image stream, the input bit rate, and the output bit rate.
JP-A-8-23539 JP-A-8-51631

  However, in the above-mentioned conventional method, a target code amount at the time of re-encoding is set according to the code amount of the input compressed moving image stream, and almost one-way regardless of the scene characteristics of the moving image and the code amount required for encoding. As described above, since the generated code amount is reduced, there is a problem that image quality is deteriorated.

  The present invention provides a compressed moving image re-encoding device and a compressed moving image re-encoding method that realize a reduction in processing delay, an improvement in image quality, and an improvement in encoding efficiency when re-encoding a compressed moving image. The purpose is to: More specifically, the present invention relates to a re-encoding device for compressed moving image data which can be processed in real time, and a re-encoding device for re-encoding moving image data with higher efficiency and higher image quality. An object of the present invention is to provide a moving picture re-encoding method.

  According to the first aspect of the present invention, an input compressed moving image stream generated by compression-encoding moving image data is used as an input signal, re-encoded at a predetermined average bit rate and at a variable bit rate, and the bit rate is changed. Means for calculating a quantization width used for the re-encoding, wherein the calculated quantization width and the quantization width in the input compressed video stream are output from a compressed moving image re-encoding device having an output compressed video stream as an output signal. And a means for outputting a quantization width used for actual re-encoding.

  According to a second aspect of the present invention, in the compressed moving picture re-encoding device according to the first aspect, a larger quantization width is selected from a quantization width used for the re-encoding and a quantization width in the input compressed video stream. It is characterized by further comprising means.

  According to a third aspect of the present invention, in the compressed moving image re-encoding device according to the first or second aspect, the quantization width and the code amount of either the input compressed moving image stream or the re-encoded compressed moving image stream are determined. Means for calculating respective complexity in two or more predetermined periods or the number of pictures by using one or both; means for outputting a predetermined complexity from a plurality of the complexity; Means for calculating the quantization width using the set average bit rate and the output complexity, and the quantization width for each predetermined period from the excess or deficiency of the target code amount and the actual code amount. Is adjusted to obtain a quantization width used for the re-encoding.

  According to a fourth aspect of the present invention, in the compressed moving picture re-encoding device according to the third aspect, re-encoding is performed from the start of re-encoding as a plurality of pictures used as the predetermined period or the number of pictures. A feature is to use a plurality of pictures including one immediately preceding picture or one intra-coded picture.

  According to a fifth aspect of the present invention, in the compressed moving picture re-encoding device according to the third or fourth aspect, a picture is divided during the predetermined period in which a basic quantization width is adjusted from the target code amount and the excess or deficiency amount. It is characterized by using a set of blocks.

  According to a sixth aspect of the present invention, in the compressed moving picture re-encoding device according to the third or fourth aspect, there is further provided means for selecting a minimum complexity among the plurality of complexity.

  According to a seventh aspect of the present invention, in the compressed moving picture re-encoding apparatus according to any one of the third to sixth aspects, the quantization width of the input compressed moving image stream used in the calculation of the complexity is determined by an image. It is characterized by further comprising means for weighting by characteristics and adjusting the quantization width.

  According to an eighth aspect of the present invention, in the compressed moving picture re-encoding device according to the seventh aspect, a predetermined period is determined by using one or both of a quantization width and a code amount of the input compressed moving image stream. Alternatively, the image processing apparatus further includes means for calculating a ratio between each complexity in the number of pictures and the complexity to be re-encoded, weighting the quantization width, and adjusting the quantization width.

  According to a ninth aspect of the present invention, in the compressed moving image re-encoding device according to the first aspect, two or more types of predetermined moving image streams are used by using one or both of a quantization width and a code amount of the input compressed moving image stream. Means for calculating each complexity in a predetermined period or the number of pictures, means for outputting a predetermined complexity from the plurality of complexity, and the preset average bit rate and the output complexity Means for calculating the quantization width by using the quantization width of the input compressed video stream, means for calculating the average of the quantization width for each predetermined period or the number of pictures, and the quantization width and the average Means for calculating an addition value using the quantization width, and calculating an addition quantization width obtained by adding the addition value to the quantization width of the input compressed video stream; and an excess / deficiency amount between the target code amount and the actual code amount. From place Wherein by adjusting the added quantization width for each period, characterized by a quantization width used for re-encoding.

  According to a tenth aspect of the present invention, in the compressed moving image re-encoding device according to the first aspect, two or more types of predetermined moving image are provided by using one or both of a quantization width and a code amount of the input compressed moving image stream. Means for calculating respective complexity in a predetermined period or the number of pictures, means for outputting a predetermined complexity from the plurality of complexity, the preset average bit rate, and the output complexity Means for calculating the quantization width by using the quantization width of the input compressed video stream, and by using the quantization prediction width of the input compressed video stream in accordance with the encoding prediction mode of the input compressed video stream, Means for calculating an average of the quantization widths, calculating an addition value for each encoding prediction mode using the quantization widths and the average quantization widths, and calculating a quantization width of the input compressed video stream. Means for calculating an added quantization width obtained by adding the added value, and adjusting the added quantization width for each predetermined period based on the excess or deficiency of the target code amount and the actual code amount, to obtain a quantum used for re-encoding. It is characterized in that it has a width.

  According to an eleventh aspect of the present invention, in the compressed moving picture re-encoding device according to the eighth or ninth aspect, a threshold value is set for a predetermined plurality of quantization widths with respect to the additional quantization width. .

  According to a twelfth aspect of the present invention, in the compressed moving picture re-encoding device according to the first aspect, a minimum value is set for a quantization width used for the re-encoding.

  According to a thirteenth aspect of the present invention, an input compressed moving image stream generated by compression-encoding moving image data is used as an input signal, re-encoded at a predetermined average bit rate and at a variable bit rate, and the bit rate is changed. In a compressed moving image re-encoding method using an output compressed video stream as an output signal, a step of calculating a quantization width used for the re-encoding, the calculated quantization width and a quantization width in the input compressed video stream. And outputting a quantization width used for actual re-encoding.

  According to a fourteenth aspect of the present invention, in the compressed moving image re-encoding method according to the thirteenth aspect, a larger quantization width is selected from a quantization width used for the re-encoding and a quantization width in the input compressed moving image stream. The method further comprises a step.

  According to a fifteenth aspect of the present invention, there is provided the compressed moving image re-encoding method according to the fourteenth aspect, wherein one of the quantization width and the code amount in the input compressed moving image stream or the re-encoded compressed moving image stream. Using both, calculating the complexity of each of two or more predetermined periods or the number of pictures; outputting a predetermined complexity from the plurality of complexity; Calculating the quantization width using the averaged bit rate and the output complexity, and adjusting the quantization width at predetermined intervals from an excess or deficiency between a target code amount and an actual code amount. And a quantization width used for the re-encoding.

  As is clear from the above description, the compressed moving image re-encoding device and the compressed moving image re-encoding method of the present invention calculate a quantization width used for re-encoding, and calculate the calculated quantization width and input compression. The quantization width in the video stream is input, and the quantization width used for actual re-encoding is output. Therefore, the scene characteristics of the moving image are obtained using the encoding information included in the input compressed video stream, the quantization width is set according to the characteristics, and the target code amount and the actual code amount are set with respect to the set quantization width. By performing the correction using the difference with the amount, it is possible to realize control such that the image quality becomes constant over a certain period, the average bit rate is satisfied, and the target code amount approaches. Thereby, high-quality re-encoding can be achieved. In addition, since the entire compressed moving image stream is decoded and re-encoded without obtaining the characteristics of the moving image, re-encoding of the compressed moving image stream can be achieved with low delay and in real time.

  Next, embodiments of a compressed moving picture re-encoding device and a compressed moving picture re-encoding method according to the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 to FIG. 11 show an embodiment of a compressed moving picture re-encoding device and a compressed moving picture re-encoding method of the present invention.

  FIG. 1 is a diagram for explaining a compressed moving picture re-encoding device according to the present invention. Here, it is assumed that MPEG-2 VIDEO is used as the compression encoding method. However, the compression encoding method is not limited to MPEG-2 VIDEO, and any other compression encoding method that controls the code amount by a quantization width may be used. Good. For example, a method such as ISO / ICE IS11172 (MPEG-1 VIDEO) or ITU-T H.261 or ITU-T H.263 may be used. In addition, the period of calculating the complexity is a group of pictures composed of all pictures coded from the start of coding to the present and a plurality of pictures, and the excess and deficiency of the target code amount and the actual code amount are adjusted. The period is a macroblock unit.

  This coding unit is only an example of an image coding unit, and the period for calculating the complexity is a unit for controlling the image quality for a certain period, and the period for adjusting the excess or deficiency is finer. It is sufficient that the unit is smaller than the period in which the complexity calculation for controlling is performed. In addition, as a unit of a picture group, there are a plurality of picture groups including one picture predicted in a frame, one picture, a picture at a certain time, and the like. Here, according to FIG. 1, the compressed moving picture re-encoding device of the present invention includes a decoding path unit 11, an error compensating unit 12, an encoding path unit 13, and a code amount control unit 14.

  First, an MPEG-2 bit stream is supplied as an input to the decoding path unit 11. The decoding path unit 11 performs variable-length decoding and inverse quantization of the input bit stream, and performs a bit rate of the input bit stream, a frame rate, a quantization width of the input bit stream for each macro block, and an input bit stream. The code amount is supplied to the code amount control means 14. In addition, the decoding path unit 11 supplies the DCT coefficient, the motion vector, and the like to the error compensating unit 12, and supplies the coding path unit 13 with coding information that can be reused at the time of re-coding.

  The error compensating unit 12 uses the DCT coefficients before re-quantization supplied from the decoding path unit 11, motion vectors and the like, and the DCT coefficients after re-quantization supplied from the encoding path unit 13 to re- DCT coefficients for preventing accumulation of errors due to quantization and performing re-quantization are supplied to the encoding path unit 13.

  In the coding path unit 13, the coding information supplied from the decoding path unit 11, the DCT coefficient supplied from the error compensating unit 12, the quantization width supplied from the code amount control unit 14, Using the target average bit rate, the DCT coefficients are re-quantized and re-encoded to output an output bit stream, and the code amount after re-encoding is supplied to the code amount control unit 14.

  In the code amount control unit 14, the bit rate of the input bit stream supplied from the decoding path unit 11, the frame rate, the quantization width of the input bit stream, the code amount of the input bit stream, The quantization width is calculated using the supplied code amount after re-encoding and the target average bit rate supplied from the outside, and supplies the calculated quantization width to the encoding path unit 13. Here, the code amount control unit 14 includes a complexity calculation unit 101, a picture group quantization width calculation unit 102, a quantization width adjustment unit 103, and a quantization width selector 104.

  The complexity calculation means 101 uses the quantization width of the input bit stream supplied from the decoding path unit 11 for each macroblock and the code amount of the input bit stream to calculate the picture group complexity and coding of a plurality of pictures. The complexity of all the performed pictures is calculated and supplied to the picture group quantization width calculation means 102.

  In the picture group quantization width calculation means 102, the frame rate supplied from the decoding path unit 11, the target average bit rate supplied from the outside, the complexity supplied from the complexity calculation means 101, the picture group complexity Is used to calculate the basic quantization width, and the calculated result is supplied to the quantization width adjustment unit 103.

  The quantization width adjusting unit 103 uses the bit rate of the input bit stream supplied from the decoding path unit 11, the frame rate, the code amount of the input bit stream, and the target average bit rate supplied from the outside to set the target code. The amount is set, a difference from the re-encoded code amount supplied from the encoding path unit 13 is obtained, and the basic quantization width supplied from the picture group quantization width calculation unit 102 is adjusted according to the difference. Then, the adjusted quantization width is supplied to the quantization width selector 104.

  In the quantization width selector 104, if the quantization width supplied from the quantization width adjusting unit 103 is smaller than the quantization width of the input bit stream supplied from the decoding path unit 11, the input bit stream The quantization width is supplied to the encoding path unit 13.

  Next, an operation example of the code amount control means 14 of the present invention will be described. Expressions (1) to (16) shown below are processing examples in the complexity calculation, and these expressions represent processing examples in the complexity calculation 101. In the complexity calculation 101, the quantization width accumulation of the picture group in a plurality of pictures is performed using the quantization width Qoji of the input bit stream and the code amount Soj of the input bit stream supplied from the decoding path unit 11 for each macroblock. The calculated value Qop and the code amount accumulated value Sop and the complexity Xp, the quantization width accumulated value Qot and the code amount accumulated value Sot and the complexity Xt in all pictures are calculated by, for example, equations (1) to (6). Then, the picture group complexity Xp and the complexity Xt are supplied to the picture group quantization width calculation means 102. Here, the code Np represents the number of pictures in the picture group, the code Nt represents the total number of encoded pictures, and the code Nmb represents the number of macroblocks per picture.

  In the picture group quantization width calculation means 102, the frame rate FR supplied from the decoding path unit 11, the target average bit rate ABR supplied from the outside, the complexity Xt supplied from the complexity calculation means 101, Using the picture group complexity Xp, the basic quantization width Qb is calculated by, for example, Expression (7), and is supplied to the quantization width adjustment unit 103. Here, min (Xt, Xp) selects a small value of Xt and Xp. In the above calculation, the long-term scene characteristics of the input bit stream and the scene characteristics of a shorter period are realized by comparing the complexity, and by selecting a small value, it becomes a control to generate a large amount of code. In addition, it is possible to suppress a decrease in image quality.

  In the quantization width adjusting unit 103, the bit rate BR of the input bit stream supplied from the encoding path unit 11, the frame rate FR, the code amount Soj of the input bit stream, and the target average bit rate supplied from the outside Using the ABR, the picture group code amount accumulated value Sop, the picture group target code amount Tp, and the target code amount Tt of all pictures are calculated, for example, using the above-described formula (2), and the following formulas (8) and (8). Calculated by 9). Also, using the code amount Srj after re-encoding supplied from the coding path unit 13 for each macroblock, the code amount accumulated value Srt of all pictures is calculated by Expression (10), and the difference VBO is calculated by Expression (10). Determined by 11). Further, the adjustment of the basic quantization width Qb supplied from the picture group quantization means 102 is calculated by, for example, Expression (12), and the adjusted quantization width Qm is supplied to the quantization width selector 104.

  Here, the above equation (9) is the accumulated value of the picture group target code amount Tp, and the codes α and r are parameters that determine the magnitude of the control response in the difference between the generated code amount and the target average bit rate. .

  In the quantization width selector 104, if the quantization width Qm supplied from the quantization width adjusting unit 103 is smaller than the quantization width Qj of the input bit stream supplied from the decoding path unit 11, the input The quantization width Qj of the bit stream is supplied to the encoding path unit 13.

  Next, a second embodiment of the present invention is shown in FIG. In the first embodiment, the complexity calculator 101 determines the complexity and the picture group complexity using the quantization width of the input bit stream supplied from the decoding path unit 11 and the code amount of the input bit stream. calculate. According to the present embodiment, the complexity calculator 101 uses the quantization width after re-encoding supplied from the encoding path unit 13 and the code amount after re-encoding to calculate the complexity and the group of pictures. Calculate complexity.

  Next, a third embodiment of the present invention is shown in FIG. In the first embodiment, the quantization width selector 104 selects a quantization width using the quantization width supplied from the quantization width adjustment unit 103. This embodiment is obtained by adding an adaptive quantization means 901 to the block diagram shown in FIG. The adaptive quantization unit 901 further uses the quantization width of the input bit stream supplied from the decoding path unit 11 and the code amount of the input bit stream to further increase the quantization width supplied from the quantization width adjustment unit 103. It is adjusted and supplied to the quantization width selector 104.

  Next, an example of the operation of the adaptive quantization means 901 will be described. The adaptive quantization means 901 uses the quantization width Qj of the input bit stream supplied from the decoding path 11, the code amount Sj, and the quantization width Qm supplied from the quantization width adjustment means 103, for example, by using Expression (3). ) Is calculated based on the picture group complexity Xp obtained from the above equation and the following equation (13), and is supplied to the quantization width selector 104. Here, the number of pictures Np in the picture group does not need to be the same as the number of pictures in the picture group used in the complexity calculation means 101. In the present embodiment, the calculation of the activity performed using the normal image signal is performed by using the quantization width and the code amount of the input bit stream to correct the quantization width. As a result, adaptive quantization using the characteristics of an image can be performed even for a compressed image re-encoding device having a configuration in which decoding is not performed up to the image signal level.

  Next, a fourth embodiment of the present invention is shown in FIG. In the first embodiment, in the picture group complexity 101, the quantization width of the input bit stream is used for calculating the complexity. This embodiment is obtained by adding an inverse adaptive quantizer 1001 to the block diagram shown in FIG.

  In the inverse adaptive quantizer 1001, the quantization width of the input bit stream supplied from the decoding path unit 11 is calculated using the quantization width of the bit stream supplied from the decoding path unit 11 and the code amount of the input bit stream. Is adjusted and supplied to the complexity calculation means 101. As an operation example of the inverse adaptive quantization means 1001, for example, the inverse transform of the adaptive quantization means 901 in FIG. 3 can be considered. In the present embodiment, in order to calculate the complexity, the quantization width of the input bit stream is adjusted using the quantization width of the input bit stream and the code amount of the input bit stream. As a result, it is possible to estimate the quantization width before adaptive quantization even for the quantization width of the input bit stream that has been adaptively quantized at the time of encoding. Can be used to calculate the complexity.

  Next, a fifth embodiment of the present invention is shown in FIG. In the present embodiment, an external input of the quantization width selector 104 is added to FIG. In the quantization width selector 1101 according to the first embodiment, the quantization width supplied from the quantization width adjustment unit 103 is smaller than the quantization width of the input bit stream supplied from the decoding path unit 11. For example, the quantization width of the input bit stream is supplied to the encoding path unit 13. In the quantization width selector 1101 of the present embodiment, in addition to the above input, the minimum quantization width is supplied from the outside, and the quantization width supplied from the quantization width adjustment unit 103 and the quantization width of the input bit stream are If the value is smaller than the minimum quantization width, the minimum quantization width is supplied to the encoding path unit 13. As a result, in the present embodiment, it is possible to suppress the occurrence of useless codes caused by setting the quantization width too small.

  Next, a sixth embodiment of the present invention is shown in FIG. This embodiment is obtained by adding a maximum bit rate quantization width calculating means 1201 to the block diagram shown in FIG. In the maximum bit rate quantization width calculation means 1201, the quantization width of the input bit stream supplied from the decoding path unit 11, the code amount of the input bit stream, the bit rate and frame rate of the input bit stream, the decoding path unit The maximum bit rate not exceeding the specified maximum bit rate using the quantization width after re-encoding supplied from 13, the code amount after re-encoding, the maximum bit rate externally supplied, etc. The quantization width is set and supplied to the quantization width selector 104.

  The quantization width selector 1202 uses the maximum bit rate quantization width supplied from the maximum bit rate quantization width calculation unit 1201 in addition to the above input, and uses the quantization width supplied from the quantization width adjustment unit 103. If the quantization width of the input bit stream is smaller than the maximum bit rate quantization width, the maximum bit rate quantization width is supplied to the encoding path unit 13. Here, as a method of calculating the maximum bit rate quantization width in the maximum bit rate quantization width calculation unit 1201, for example, the target bit rate and the maximum bit rate ratio of the input bit stream and the code amount of the input bit stream are used to calculate the target bit rate. This can be realized by setting the code amount and calculating the quantization width in macroblock units using code amount control that satisfies the target code amount. In the present embodiment, when the bit rate of the input bit stream is very high and the target average bit rate is low, the coding width is set too small more than necessary, and the occurrence of useless codes can be suppressed. .

  Next, a seventh embodiment of the present invention is shown in FIG. In the present embodiment, the code amount control unit 14 includes a complexity calculation unit 101, a picture group quantization width calculation unit 102, a quantization width adjustment unit 103, a quantization width selector 104, and an average quantization width calculation unit. It comprises means 1301 and addition value calculating means 1302.

  Hereinafter, only the portions different from the first embodiment will be described. The average quantization width calculation unit 1301 accumulates the quantization width of the input bit stream supplied from the decoding path unit 11 for a plurality of picture periods, and supplies the average value to the addition value calculation unit 1302.

  The addition value calculation means 1302 calculates a difference value between the basic quantization width supplied from the picture group quantization width calculation means 102 and the average quantization width supplied from the average quantization width calculation means 1301 by using the decoding path unit 11. Is added to the quantization width of the input bit stream supplied from the sub-block and supplied to the quantization width adjustment unit 103.

  Next, an example of the operation of the average quantization width calculation means 1301 and the added value calculation means 1302 will be described. In the average quantization width calculating means 1301, the average quantization width Qave is calculated by the above expression (1) and the following expression (14) using the quantization width Qj supplied from the decoding path unit 11, and added. It is supplied to the value calculation means 1302. Here, the number of pictures Np in the picture group does not need to be the same as the number of pictures in the picture group used in the complexity calculation means 101.

  The addition value calculation means 1302 calculates the addition value A by using the quantization width Qb supplied from the picture group quantization width calculation means 102 and the average quantization width Qave supplied from the average quantization width calculation means 1301, for example. It is calculated by the following equation (15) and supplied to the quantization width adjusting means 103. Accordingly, in the present embodiment, since the added value is added to the quantization width of the input bit stream, if the quantization width is set using adaptive quantization during encoding, the quantization is performed without considering the adaptive quantization. You can set the width.

  Next, an eighth embodiment of the present invention is shown in FIG. In the present embodiment, an external input to the addition value calculation means 1302 is added to FIG. In the addition value calculation means 1302 of the seventh embodiment, the difference value between the basic quantization width supplied from the picture group quantization width calculation means 102 and the average quantization width supplied from the average quantization width calculation means 1301 Is added to the quantization width of the input bit stream supplied from the decoding path unit 11 to calculate the quantization width.

  In the quantization width setting unit 1401 of the present embodiment, a minimum quantization width or a threshold is supplied from outside in addition to the above input. The addition value calculation means 1401 selects a quantization width by comparing the calculated quantization width with the quantization width or the threshold, and supplies the quantization width to the quantization width adjustment means 103.

  FIG. 9 shows an operation example of the addition value calculation means. FIG. 9 shows which quantization width is selected when the minimum quantization width and the threshold are set. The horizontal axis represents the quantization width of the input bit stream, and the vertical axis represents the quantization width after re-encoding. The thick line in the graph is the quantization width selected by the main quantization width setting.

  Here, the minimum quantization width is set by the minimum quantization width, and after a certain quantization width by the threshold, the quantization after re-encoding is performed until the quantization width of the input bit stream exceeds the threshold. The quantization width is set so that the width does not exceed the threshold. Thus, in the present embodiment, the generation of an excessive code amount is suppressed by setting the minimum value of the quantization width after requantization. In addition, a quantization width larger than the threshold value is not selected to suppress image quality deterioration.

  Next, a ninth embodiment of the present invention will be described. In the seventh and eighth embodiments, the same addition value is added to the quantization width of the input bit stream in any of the coding prediction methods. In the ninth embodiment, an addition value is held for each picture coding prediction method. For example, the average quantization width calculation unit 1301 encodes the intra-frame encoding (I picture), the forward inter-frame encoding (P picture), and the bidirectional inter-frame encoding (B picture) in MPEG-2. The average quantization width Qave is calculated for each mode and supplied to the addition value calculation means 1302.

  The addition value calculation means 1302 calculates a difference value between the basic quantization width supplied from the picture group quantization width calculation means 102 and the average quantization width for each coding mode supplied from the average quantization width calculation means 1301. , Is added to the quantization width of the input bit stream supplied from the decoding path unit 11 for each encoding mode, and the quantization width is calculated. As a result, in the present embodiment, since the addition value is switched according to the encoding mode, finer control than with a single addition value is possible, and the image quality can be improved.

  In the above-described embodiment, for example, consider that the input compressed video stream 1 is re-encoded and the compressed video stream 2 is output. FIG. 10 shows an example of the relationship between the average quantization width per picture and time in the compressed moving image stream 1 and the compressed moving image stream 2 after re-encoding, and FIG. 11 shows an example of the relationship between the generated code amount and time at that time. is there. The thin solid line in FIG. 10 and FIG.

  In general, the code amount can be reduced by setting a quantization width larger than the quantization width in the compressed moving image stream 1 and performing re-quantization. Incidentally, in the conventional method, a target code amount at the time of re-encoding is set according to the code amount of the compressed moving image stream 1, and a quantization width is set. For example, in the case of FIG. 11, it is necessary to reduce a substantially constant code amount in any period, so that the quantization width is set uniformly large. As a result, as shown by the dashed line in FIG. 10, even for a picture with a large quantization width of the input compressed moving image stream and poor image quality, a larger value is set at the time of re-encoding, which may cause image quality deterioration. Become. Therefore, such a problem can be solved by setting the quantization width according to the scene characteristics of the moving image as shown by the thick solid line in FIG. According to the present invention, scene characteristics of a moving image are obtained using coding information included in an input compressed moving image stream, and a quantization width according to the characteristics is set.

  Next, the set quantization width is corrected using the difference between the target code amount obtained using the average bit rate and the like and the actual code amount. As a result, control can be realized such that the image quality is constant over a certain period, the average bit rate is satisfied, and the target code amount approaches. In addition, by preventing the quantization width from being smaller than the quantization width of the input compressed moving image stream, it is possible to improve the average image quality without allocating an unnecessarily large amount of code. Furthermore, in the present invention, since the entire compressed moving image stream is once decoded and re-encoded without obtaining the characteristics of the moving image, real-time processing with little delay can be realized.

  The above embodiment is an example of a preferred embodiment of the present invention. However, the present invention is not limited to this, and various modifications can be made without departing from the scope of the present invention.

1 is a block diagram illustrating a configuration example of an embodiment of a compressed moving picture re-encoding device of the present invention. It is a block diagram showing an example of composition of a compression moving picture re-encoding device in a 2nd embodiment. It is a block diagram showing the example of composition of the compression moving picture re-encoding device in a 3rd embodiment. It is a block diagram showing the example of composition of the compression moving picture re-encoding device in a 4th embodiment. It is a block diagram showing the example of composition of the compression moving picture re-encoding device in a 5th embodiment. It is a block diagram showing the example of composition of the compression moving picture re-encoding device in a 6th embodiment. It is a block diagram showing the example of composition of the compression moving picture re-encoding device in a 7th embodiment. It is a block diagram showing the example of composition of the compression moving picture re-encoding device in an 8th embodiment. FIG. 28 is an explanatory diagram of an operation example of a quantization width setting unit in the eighth embodiment. FIG. FIG. FIG. 11 is a block diagram illustrating a configuration of a conventional decoder. FIG. 11 is a block diagram illustrating a configuration of a conventional encoder. FIG. 11 is a block diagram illustrating a configuration example of a conventional compressed moving image re-encoding device. FIG. 11 is a block diagram illustrating a configuration example of a conventional compressed moving image re-encoding device. FIG. 11 is a block diagram illustrating a configuration example of a conventional compressed moving image re-encoding device.

Explanation of reference numerals

Reference Signs List 11 decoding path unit 12 error compensation unit 13 encoding path unit 14 code amount control means 101 complexity calculation means 102 picture group quantization width calculation means 103 quantization width adjustment means 104 quantization width selector 201 variable length decoder 202 inverse Quantizer 203 Inverse discrete cosine transformer 204 Adder 205 Frame memory 206 Motion compensation predictor 301 Subtractor 302 Discrete cosine transformer 303 Quantizer 304 Variable length encoder 305 Code amount control means 306 Inverse quantizer 307 Inverse Discrete cosine transformer 308 Adder 309 Frame memory 310 Motion compensation predictor 41 Decoding path unit 42 Error compensating unit 43 Encoding path unit 401 Code amount control unit 51 Decoding path unit 52 Encoding path unit 501 Code amount control unit 61 Decoding path Unit 62 error compensating unit 63 encoding path unit 601 subtraction 602 inverse quantizer 603 subtractor 604 inverse discrete cosine transformer 605 frame memory 606 motion compensation predictor 607 discrete cosine transformer 608 code amount control means 901 adaptive quantization means 1001 inverse adaptive quantization means 1101 quantization width selector 1201 Maximum bit rate quantization width calculation means 1202 Quantization width selector 1301 Average quantization width calculation means 1302, 1401 Addition value calculation means

Claims (15)

An input compressed video stream generated by compression-coding moving image data is used as an input signal, and an output compressed video stream with a changed average bit rate and a variable bit rate is re-encoded at a predetermined average bit rate, and the output compressed video stream having a changed bit rate is output as an output signal. Compressed video re-encoding device,
Means for calculating a quantization width used for the re-encoding,
Means for inputting the calculated quantization width and the quantization width in the input compressed video stream and outputting a quantization width used for actual re-encoding. .   2. The apparatus according to claim 1, further comprising means for selecting a larger quantization width from the quantization width used for the re-encoding and the quantization width in the input compressed video stream. . In either the input compressed moving image stream or the re-encoded compressed moving image stream, using one or both of the quantization width and the code amount, each of the two or more predetermined predetermined periods or the number of pictures is used. Means for calculating complexity;
Means for outputting a predetermined complexity from the plurality of complexity,
Means for calculating the quantization width using the preset average bit rate and the output complexity,
3. The quantization width used for the re-encoding by adjusting the quantization width every predetermined period from an excess or deficiency of a target code amount and an actual code amount. Compressed video re-encoding device.   As the plurality of pictures used as the predetermined period or the number of pictures, a plurality of pictures including one picture immediately before the current re-encoding or one intra-coded picture from the start of re-encoding is used. The compressed moving picture re-encoding device according to claim 3, wherein   5. The compressed moving picture recoding apparatus according to claim 3, wherein a set of blocks obtained by dividing a picture is used in the predetermined period in which a basic quantization width is adjusted based on the target code amount and the excess or deficiency amount. Device.   5. The apparatus according to claim 3, further comprising: means for selecting a minimum complexity among the plurality of complexity.   7. The apparatus according to claim 3, further comprising: means for weighting a quantization width of the input compressed moving image stream used for calculating the complexity by image characteristics, and adjusting the quantization width. A compressed video re-encoding device according to any one of claims 1 to 3.   Using either or both of the quantization width and code amount of the input compressed video stream, calculate the ratio of the respective complexity and the complexity of the re-encoding target in a predetermined period or the number of pictures. 8. The apparatus according to claim 7, further comprising means for weighting the quantization width and adjusting the quantization width. Means for calculating the complexity of each of the two or more predetermined periods or the number of pictures using one or both of the quantization width and the code amount of the input compressed video stream,
Means for outputting a predetermined complexity from the plurality of complexity,
Means for calculating a quantization width using the preset average bit rate and the output complexity,
Using the quantization width of the input compressed video stream, means for calculating an average of the quantum width for each predetermined period or number of pictures,
Means for calculating an addition value using the quantization width and the average quantization width, and calculating an addition quantization width obtained by adding the addition value to the quantization width of the input compressed video stream;
2. The compression method according to claim 1, wherein the additional quantization width is adjusted every predetermined period from the excess or deficiency of the target code amount and the actual code amount to obtain a quantization width used for re-encoding. Moving image re-encoding device. Means for calculating the complexity of each of the two or more predetermined periods or the number of pictures using one or both of the quantization width and the code amount of the input compressed video stream,
Means for outputting a predetermined complexity from the plurality of complexity,
Means for calculating a quantization width using the preset average bit rate and the output complexity,
Using the quantization width of the input compressed video stream, according to the encoding prediction mode of the input compressed video stream, means for calculating the average of the respective quantization width for each predetermined period or number of pictures,
Means for calculating an addition value for each coding prediction mode using the quantization width and the average quantization width, and calculating an addition quantization width obtained by adding the addition value to the quantization width of the input compressed video stream. ,
2. The compression method according to claim 1, wherein the additional quantization width is adjusted every predetermined period from the excess or deficiency of the target code amount and the actual code amount to obtain a quantization width used for re-encoding. Moving image re-encoding device.   The apparatus according to claim 8, wherein a threshold value is set for a predetermined plurality of quantization widths with respect to the added quantization width.   2. The apparatus according to claim 1, wherein a minimum value is set for a quantization width used for the re-encoding. An input compressed video stream generated by compressing and encoding moving image data is used as an input signal, an output compressed video stream having a predetermined average bit rate and re-encoded at a variable bit rate, and an output compressed video stream having a changed bit rate is output. Compressed video re-encoding method,
Calculating a quantization width used for the re-encoding,
Inputting the calculated quantization width and the quantization width in the input compressed video stream, and outputting a quantization width used for actual re-encoding. .   14. The method according to claim 13, further comprising the step of selecting a larger quantization width from the quantization width used for the re-encoding and the quantization width in the input compressed video stream. . In either the input compressed moving image stream or the re-encoded compressed moving image stream, using one or both of the quantization width and the code amount, each of the two or more predetermined predetermined periods or the number of pictures is used. Calculating the complexity;
Outputting a predetermined complexity from the plurality of complexity,
Calculating the quantization width using the preset average bit rate and the output complexity;
15. The quantization width used for the re-encoding by adjusting the quantization width for each predetermined period from the excess or deficiency of the target code amount and the actual code amount. Compressed video re-encoding method.

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