US20090213928A1 - Transcoder - Google Patents

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US20090213928A1
US20090213928A1 US12/360,350 US36035009A US2009213928A1 US 20090213928 A1 US20090213928 A1 US 20090213928A1 US 36035009 A US36035009 A US 36035009A US 2009213928 A1 US2009213928 A1 US 2009213928A1
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period
bit rate
stream
target
ratio
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Hiromu Hasegawa
Nobuyuki Takasu
Makoto Saito
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MegaChips Corp
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MegaChips Corp
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Publication of US20090213928A1 publication Critical patent/US20090213928A1/en
Priority to US13/401,198 priority Critical patent/US9071837B2/en
Priority to US14/706,126 priority patent/US9749637B2/en
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/134—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or criterion affecting or controlling the adaptive coding
    • H04N19/146—Data rate or code amount at the encoder output
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/134—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or criterion affecting or controlling the adaptive coding
    • H04N19/146—Data rate or code amount at the encoder output
    • H04N19/15—Data rate or code amount at the encoder output by monitoring actual compressed data size at the memory before deciding storage at the transmission buffer
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/102—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or selection affected or controlled by the adaptive coding
    • H04N19/103—Selection of coding mode or of prediction mode
    • H04N19/114—Adapting the group of pictures [GOP] structure, e.g. number of B-frames between two anchor frames
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/102—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or selection affected or controlled by the adaptive coding
    • H04N19/115—Selection of the code volume for a coding unit prior to coding
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/102—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or selection affected or controlled by the adaptive coding
    • H04N19/124—Quantisation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/102—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or selection affected or controlled by the adaptive coding
    • H04N19/124—Quantisation
    • H04N19/126—Details of normalisation or weighting functions, e.g. normalisation matrices or variable uniform quantisers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/134—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or criterion affecting or controlling the adaptive coding
    • H04N19/157—Assigned coding mode, i.e. the coding mode being predefined or preselected to be further used for selection of another element or parameter
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/134—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or criterion affecting or controlling the adaptive coding
    • H04N19/162—User input
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/169—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/169—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding
    • H04N19/177—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being a group of pictures [GOP]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/40—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using video transcoding, i.e. partial or full decoding of a coded input stream followed by re-encoding of the decoded output stream
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/60—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using transform coding
    • H04N19/61—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using transform coding in combination with predictive coding

Definitions

  • the present invention relates to a transcoder for converting an input stream by decoding into a different output stream, and more particularly to a technique to appropriately control the amount of generated codes of the output stream toward a target bit rate.
  • Images to be delivered on digital broadcasts, those to be stored in media such as DVDs and hard disks, and the like are compressed in accordance with various coding systems.
  • the object for such compressions is to avoid constraint on a transmission band, increase the transmission speed, decrease the memory size or the like.
  • Japanese Patent Application Laid Open Gazette No. 2006-74635 relates to a transcoder for converting an image compressed in a first compressive coding system into an image compressed in a second compressive coding system.
  • This transcoder uses intermediate information generated during the decoding of the image compressed in the first compressive coding system to compress the image in the second compressive coding system.
  • bit rate conversion is performed on the basis of the bit rate in a unit of GOP (Group Of Pictures) of the input stream and the target bit rate in a unit of GOP of the output stream.
  • a unit of GOP is set as a control unit time of a rate control. This is based on the premise that the picture structure in the GOPs of the input stream is constant to some degree in the whole sequence, and it is not assumed that the bit rate varies sharply on a GOP basis in the input stream.
  • the present invention is intended for a transcoder for converting a first stream into a second stream.
  • the transcoder comprises a period determination part for determining a control unit time, a part for acquiring a bit rate of a first stream per determined control unit time, and a quantization step value calculation part for calculating a quantization step value of a second stream by using information on a first stream including an acquired bit rate of a first stream per control unit time, and in the transcoder of the present invention, the period determination part determines each control unit time so that each control unit time has frames of which number is not less than a predetermined value.
  • the variation of the bit rate of the first stream per control unit time can be reduced to be smaller and it is thereby possible to appropriately perform the control on the bit rate.
  • the transcoder comprises a period determination part for determining a control unit time, a part for acquiring a bit rate of a first stream per determined control unit time, and a quantization step value calculation part for calculating a quantization step value of a second stream by using information on a first stream including an acquired bit rate of a first stream per control unit time, and in the transcoder of the present invention, the period determination part determines each control unit time so that the ratio of I picture frames included in each control unit time becomes not more than a predetermined ratio.
  • the variation of the bit rate of the first stream per control unit time can be reduced to be smaller and it is thereby possible to appropriately perform the control on the bit rate.
  • FIG. 1 is a block diagram showing a transcoder
  • FIG. 2 is a view showing information on an input stream (first stream) and an output stream (second stream) by control unit time;
  • FIGS. 3A and 3B are views showing a method of correcting the control unit time (exemplary case where no correction is made) in accordance with a first preferred embodiment
  • FIGS. 4A and 4B are views showing a method of correcting the control unit time in accordance with the first preferred embodiment
  • FIGS. 5A and 5B are views showing another method of correcting the control unit time in accordance with the first preferred embodiment
  • FIGS. 6A and 6B are views showing still another method of correcting the control unit time in accordance with the first preferred embodiment
  • FIGS. 7A and 7B are views showing a method of correcting the control unit time (exemplary case where no correction is made) in accordance with a second preferred embodiment
  • FIGS. 8A and 8B are views showing a method of correcting the control unit time in accordance with the second preferred embodiment
  • FIGS. 9A and 9B are views showing another method of correcting the control unit time in accordance with the second preferred embodiment.
  • FIGS. 10A and 10B are views showing still another method of correcting the control unit time in accordance with the second preferred embodiment.
  • FIG. 1 is a block diagram showing a transcoder 1 in accordance with the preferred embodiments.
  • the transcoder 1 comprises a decoder 2 and an encoder 3 .
  • the decoder 2 inputs a first stream.
  • the first stream is a stream of coded image.
  • the decoder 2 decodes the first stream and outputs uncompressed image data to the encoder 3 .
  • the encoder 3 recodes the uncompressed image data which is decoded by the decoder 2 and outputs a second stream.
  • the transcoder 1 converts a coding system of stream, and for example, inputs a first stream coded in MPEG2 and outputs a second stream coded in H.264.
  • the present invention is devised in order to optimally control the rate of the second stream to be outputted in the conversion.
  • the transcoder 1 outputs a stream of the same coding system, and for example, inputs a first stream coded in MPEG2 and outputs a second stream recoded in MPEG2.
  • the present invention is devised in order to optimally control the rate of the second stream to be outputted.
  • various computations are performed in the decoder 2 and the encoder 3 , and these computations performed in the decoder 2 and the encoder 3 may be implemented by hardware or may be implemented by software operations.
  • the decoder 2 and the encoder 3 may be constructed as hardware circuits or implemented by a CPU and programs stored in memories. Alternatively, there may be a case where some of the computations are performed by hardware and the others are performed by software.
  • FIG. 2 is a view showing information on streams that the transcoder 1 inputs or outputs, by control unit time.
  • the control unit time L n is referred to as “the n-th period” as appropriate.
  • one GOP is set as the control unit time L n basically, a plurality of successive GOPs are set as the control unit time L n in accordance with the state of the input stream as discussed later.
  • the control unit time L n however, one frame, a plurality of successive frames, or the like may be set.
  • a total input bit rate S of the first stream is acquired from a sequence header or the like.
  • An average input bit rate S n is an average bit rate of the first stream in the n period.
  • the transcoder 1 comprises a buffer and can store information on average input bit rates S n for M periods. Specifically, the buffer can store information on the average input bit rates S n from the (n ⁇ M+1) period to the n period.
  • An average period bit rate AS n is an average value of the average input bit rates S n from the (n ⁇ M+1) period to the n period.
  • the average period bit rate AS n is expressed by Eq. 1.
  • the decoder 2 acquires information on the total input bit rate S, the average input bit rate S n , the average period bit rate AS n , the quantization step value P in the n period or the like from the inputted first stream and outputs these information to the encoder 3 .
  • the encoder 3 uses these information to recode the image.
  • a total target bit rate T of the second stream is set by a user.
  • the user uses a not-shown operation part included in the transcoder 1 to set the total target bit rate T.
  • a target setting bit rate T n is a target bit rate of the second stream in the n period.
  • An average output bit rate C n is an average bit rate of the second stream converted in the n period.
  • the transcoder 1 comprises a buffer and can store information on the average output bit rates C n for M periods. Specifically, the buffer can store information on the average output bit rates C n from the (n ⁇ M+1) period to the n period.
  • An average period bit rate AC n is an average value of the average output bit rates C n from the (n ⁇ M+1) period to the n period.
  • the average period bit rate AC n is expressed by Eq. 2.
  • the buffer period used for calculation of the average period bit rate AS n or AC n is linked to the control unit time L n in these preferred embodiments, setting of the buffer period is not limited to this case. For example, one past frame at the point of time when coding is finished, a plurality of successive past frames, or the like may be set as the buffer period.
  • a quantization step conversion factor ⁇ n is a factor calculated at the point of time when the (n ⁇ 1) period is finished.
  • a quantization step value Q of the second stream is determined by multiplying a value P which is the quantization step value of the first stream or a value P calculated from the quantization step value of the first stream by the quantization step conversion factor ⁇ n . This relation is expressed by Eq. 3.
  • the initial value ⁇ 1 of the quantization step conversion factor ⁇ n is given by Eq. 4. Specifically, a value obtained by dividing the total target bit rate T of the second stream by the total input bit rate S of the first stream, i.e., a bit rate ratio, is substituted into function f, to obtain the initial value ⁇ 1 of the quantization step conversion factor ⁇ n .
  • the function f is a function for obtaining a ratio of quantization step values from the ratio of bit rates, and assuming that the ratio of bit rates is R B and the ratio of quantization step values is R Q , the function f is generally expressed by Eq. 5.
  • f I (x), f P (x) and f B (x) are functions corresponding to the I picture, the P picture and the B picture, respectively.
  • ⁇ f I ⁇ ( x ) ⁇ I ⁇ ( a , s ) * x - ⁇ I ⁇ ( a , s )
  • P ⁇ ( x ) ⁇ P ⁇ ( a , s ) * x - ⁇ P ⁇ ( a , s )
  • f B ⁇ ( x ) ⁇ B ⁇ ( a , s ) * x - ⁇ B ⁇ ( a , s ) ( Eq . ⁇ 7 )
  • ⁇ I (a, s), ⁇ P (a, s), ⁇ B (a, s), ⁇ I (a, s), ⁇ P (a, s), ⁇ B (a, s) represent the values of ⁇ and ⁇ which are calculated by using the act value and the sad value as parameters.
  • the activity value is obtained by calculating a differential absolute value sum of an average pixel value in a macroblock and a pixel value of each pixel in the macroblock by macroblock.
  • the activity value is an evaluation value indicating the degree of dispersion of pixels in the macroblock. This is the same as an activity value used in the code amount control model TM5 of MPEG2 or the like.
  • the motion evaluation value (sad value) is obtained by calculating an interframe differential absolute value sum of a pixel value of each pixel in a reference image macroblock and a pixel value of the corresponding pixel in a macroblock, by macroblock.
  • the motion evaluation value is obtained by comparing each pixel in a macroblock and the corresponding pixel in the reference image macroblock and calculating an absolute value sum of differentials of pixel values of corresponding pixels in the same coordinate positions.
  • ⁇ I (I Ln ), ⁇ P (I Ln ), ⁇ B (I Ln ), ⁇ I (I Ln ), ⁇ P (I Ln ) and ⁇ B (I Ln ) represent the factors ⁇ and ⁇ which are determined by using the feature value I Ln of the image as parameters.
  • the transcoder 1 calculates the quantization step conversion factor ⁇ n+1 after a lapse of the n period.
  • Eq. 9 is an equation for calculation of the quantization step conversion factor ⁇ n+1 .
  • (T ⁇ C n ) is obtained by subtracting the average output bit rate C n of the converted second stream in the n period from the total target bit rate T of the second stream. This value is referred to as a coefficient of variation.
  • “k” represents an adjustment factor used for adjusting the coefficient of variation and is a positive value.
  • the ratio of the quantization step values is adjusted toward a target by adding the coefficient of variation to the initial value ⁇ 1 obtained by Eq. 4.
  • the initial value ⁇ 1 of the quantization step conversion factor can be referred to as a reference conversion factor.
  • the quantization step value Q of the second stream in the (n+1) period is obtained by using Eq. 3.
  • the average output bit rate C n in the n period is used.
  • the average period bit rate AC n from the (n ⁇ M+1) period to the n period may be used, instead of the average output bit rate C n .
  • the value obtained by subtracting the average output bit rate C n of the converted second stream in the n period from the total target bit rate T of the second stream is used.
  • the value obtained by this subtraction may be further divided by the average input bit rate S n of the first stream in the n period.
  • ⁇ n + 1 k * ( T - C n S n ) + ⁇ 1 ( Eq . ⁇ 11 )
  • both the ideas for the methods of calculating the coefficient of variation by using Eqs. 10 and 11 may be taken. Specifically, as shown in Eq. 12, the average period bit rate AC n is used instead of the average output bit rate C n and the value obtained by subtraction is divided by the average input bit rate S n . With this, it is possible to more gently control the coefficient of variation.
  • ⁇ n + 1 k * ( T - A ⁇ ⁇ C n S n ) + ⁇ 1 ( Eq . ⁇ 12 )
  • the value obtained by subtracting the average output bit rate C n from the total target bit rate T is divided by the average input bit rate S n .
  • the value obtained by subtraction may be divided by the average period bit rate AS n of the first stream from the (n ⁇ M+1) period to the n period.
  • ⁇ n + 1 k * ( T - C n A ⁇ ⁇ S n ) + ⁇ 1 ( Eq . ⁇ 13 )
  • the average period bit rate AC n may be used instead of the average output bit rate C n and the average period bit rate AS n may be used instead of the average input bit rate S n . With this, it is possible to more gently control the coefficient of variation.
  • ⁇ n + 1 k * ( T - A ⁇ ⁇ C n A ⁇ ⁇ S n ) + ⁇ 1 ( Eq . ⁇ 14 )
  • the rate control method (B) will be discussed. Also in the rate control method (B), the quantization step conversion factor is calculated and by using Eq. 3, the quantization step value Q of the second stream is calculated. The method of calculating the quantization step conversion factor, however, is different from that in the rate control method (A). In the rate control method (A), the initial value ⁇ 1 of the quantization step conversion factor is obtained and by using the initial value ⁇ 1 as the reference conversion factor, the variations from the reference conversion factor are sequentially obtained.
  • a target setting bit rate T n+1 of the second stream in the (n+1) period is determined and by using the determined target setting bit rate T n+1 , the quantization step conversion factor ⁇ n+1 in the (n+1) period is calculated.
  • the quantization step conversion factor ⁇ n+1 is calculated by the same method as that using Eq. 5. Specifically, by using the function f shown in Eqs. 6 to 8, the quantization step conversion factor ⁇ n+1 is calculated. More specifically, as shown Eq. 15, by substituting the ratio between the target setting bit rate T n+1 in the (n+1) period and the average input bit rate S n in the n period into the function f, the quantization step conversion factor ⁇ n+1 is calculated.
  • the quantization step conversion factor ⁇ n+1 may be calculated.
  • Eq. 17 is an equation for calculation of the target setting bit rate T n+1 in the (n+1) period.
  • it represents the target setting bit rate T n+1 in the (n+1) period calculated by the transcoder 1 at the point of time when the n period is finished.
  • the target setting bit rate T n+1 in the (n+1) period can be calculated by dividing the total target bit rate T of the second stream by the target ratio.
  • T n + 1 k * T C n T n ( Eq . ⁇ 17 )
  • “k” is a positive factor and a factor for adjusting the target setting bit rate T n+1 .
  • the ratio (target ratio) between the bit rate and the target in the n period is calculated by C n /T n and then the total target bit rate T is divided by the target ratio to adjust the target setting bit rate T n+1 in the (n+1) period, thereby controlling the bit rate to approximate the target bit rate on the whole.
  • T n + 1 k * T S n - 1 S n * C n T n ( Eq . ⁇ 18 )
  • the target ratio is multiplied by S n ⁇ 1 /S n .
  • This multiplier factor S n ⁇ 1 /S n is a value obtained by dividing the average input bit rate S n ⁇ 1 of the first stream in the (n ⁇ 1) period by the average input bit rate S n of the first stream in the n period and may be referred to as a period ratio of the average input bit rate. Multiplying the target ratio by the period ratio can adjust the target ratio.
  • multiplying the target ratio by the period ratio can correct the local variation of the target ratio. For example, if the average input bit rate S n locally becomes smaller, sometimes the target ratio C n /T n accordingly becomes smaller. Also in such a case, multiplying the target ratio C n /T n by the period ratio S n ⁇ 1 /S n (the period ratio is larger than 1 in this case) makes it possible to adjust the target ratio and avoid large variation of the target setting bit rate T n+1 . Conversely, if the average input bit rate S n locally becomes larger, the period ratio S n ⁇ 1 /S n is smaller than 1 and this suppresses sharp increase of the target ratio.
  • Eq. 18 the value obtained by dividing the average input bit rate S n ⁇ 1 of the first stream in the (n ⁇ 1) period by the average input bit rate S n of the first stream in the n period is used as the period ratio.
  • the average input bit rate S n+1 may be used in the case where the average input bit rate S n+1 of the first stream in the (n+1) period.
  • the case where the average input bit rate S n+1 can be prefetched is a case where there is enough time to buffer the information on the average input bit rate S n+1 and then calculate the target setting bit rate T n+1 in the (n+1) period. In other words, this is a case where some processing delay is allowed.
  • Eq. 19 is an equation for calculation of the target setting bit rate T n+1 by using the average input bit rate S n+1 .
  • T n + 1 k * T S n S n + 1 * C n T n ( Eq . ⁇ 19 )
  • the quantization step conversion factor ⁇ n+1 in the (n+1) period can be calculated by substituting the ratio between the target setting bit rate T n+1 in the (n+1) period and the average input bit rate S n+1 in the (n+1) period into the function f.
  • S n ⁇ 1 /S n is used as the period ratio.
  • the ratio between the average period bit rate AS n ⁇ 1 of past M periods including the (n ⁇ 1) period and the average period bit rate AS n of past M periods including the n period may be used as the period ratio.
  • AS n ⁇ 1 /AS n may be used, instead of S n ⁇ 1 /S n as the period ratio. With this, it is possible to decrease the effect of local variation and optimally control the target setting bit rate T n+1 .
  • the ratio between the average period bit rate AS n of past M periods including the n period and the average period bit rate AS n+1 of past M periods including the (n+1) period may be used as the period ratio.
  • AS n /AS n+1 may be used, instead of S n ⁇ 1 /S n , as the period ratio.
  • the quantization step conversion factor ⁇ n+1 in the (n+1) period can be calculated by substituting the ratio between the target setting bit rate T n+1 in the (n+1) period and the average period bit rate AS n+1 of past M periods including the (n+1) period into the function f.
  • the average period bit rate AC n from the (n ⁇ M+1) period to the n period may be used instead of the average output bit rate C n in the n period.
  • AC n is used instead of C n . This makes it possible to more gently control the target setting bit rate T n+1 .
  • the rate control method (C) will be discussed. Also in the rate control method (C), the quantization step conversion factor is calculated, and by using Eq. 3, the quantization step value Q of the second stream is calculated. Further, in the rate control method (C), like in the rate control method (B), the target setting bit rate T n+1 of the second stream in the (n+1) period is determined at the point of time when the n period is finished, and by using the determined target setting bit rate T n+1 , the quantization step conversion factor ⁇ n+1 in the (n+1) period is calculated.
  • the quantization step conversion factor ⁇ n+1 is calculated in the same method as that discussed by using Eq. 5. In other words, by using the function f shown in Eqs. 6 to 8, the quantization step conversion factor ⁇ n+1 is calculated. Specifically, as shown in Eq. 15, the quantization step conversion factor ⁇ n+1 is calculated by substituting the ratio between the target setting bit rate T n+1 in the (n+1) period and the average input bit rate S n in the n period into the function f. Alternatively, as shown in Eq. 16, the quantization step conversion factor ⁇ n+1 may be calculated by using the average period bit rate AS n from the (n ⁇ M+1) period to the n period, instead of the average input bit rate S n .
  • Eq. 22 is an equation for calculation of the target setting bit rate T n+1 in the (n+1) period.
  • it represents the target setting bit rate T n+1 in the (n+1) period calculated by the transcoder 1 at the point of time when the n period is finished.
  • the target setting bit rate T n+1 in the (n+1) period can be calculated by adding the target difference to the total target bit rate T of the second stream.
  • T n+1 T+k *( T n ⁇ C n ) (Eq.22)
  • “k” is a positive factor and a factor for adjusting the target setting bit rate T n+1 .
  • the difference between the bit rate and the target in the n period is calculated by (T n ⁇ C n ) and then the target difference is added to the total target bit rate T, to thereby control the output stream to approximate the target bit rate.
  • T n + 1 T + k * S n S n - 1 * ( T n - C n ) ( Eq . ⁇ 23 )
  • the target difference is multiplied by S n /S n ⁇ 1 .
  • This multiplier factor S n /S n ⁇ 1 is the period ratio obtained by dividing the average input bit rate S n of the first stream in the n period by the average input bit rate S n ⁇ 1 of the first stream in the (n ⁇ 1) period. Multiplying the target difference by the period ratio can adjust the target difference.
  • multiplying the target difference by the period ratio can correct the local variation of the target difference. For example, if the average input bit rate S n in the n period locally becomes smaller than that in the (n ⁇ 1) period, sometimes the target difference (T n ⁇ C n ) accordingly varies largely. Also in such a case, multiplying the target difference (T n ⁇ C n ) by the period ratio S n /S n ⁇ 1 (the period ratio is smaller than 1 in this case) makes it possible to adjust the target difference and avoid large variation of the target setting bit rate T n+1 .
  • the value obtained by dividing the average input bit rate S n of the first stream in the n period by the average input bit rate S n ⁇ 1 of the first stream in the (n ⁇ 1) period is used as the period ratio.
  • the average input bit rate S n+1 of the first stream in the (n+1) period can be prefetched
  • the average input bit rate S n+1 may be used.
  • the case where the average input bit rate S n+1 can be prefetched is, as discussed above, a case where there is enough time to buffer the information on the average input bit rate S n+1 and then calculate the target setting bit rate T n+1 in the (n+1) period. In this case, in Eq.
  • S n+1 /S n is used, instead of S n /S n ⁇ 1 , as the period ratio.
  • the quantization step conversion factor ⁇ n+1 in the (n+1) period can be calculated by substituting the ratio between the target setting bit rate T n+1 in the (n+1) period and the average input bit rate S n+1 in the (n+1) period into the function f.
  • S n /S n ⁇ 1 is used as the period ratio.
  • the ratio between the average period bit rate AS n of past M periods including the n period and the average period bit rate AS n ⁇ 1 of past M periods including the (n ⁇ 1) period may be used as the period ratio.
  • AS n /AS n ⁇ 1 may be used, instead of S n /S n ⁇ 1 , as the period ratio. With this, it is possible to decrease the effect of local variation and optimally control the target setting bit rate T n+1 .
  • the ratio between the average period bit rate AS n+1 of past M periods including the (n+1) period and the average period bit rate AS n of past M periods including the n period may be used as the period ratio.
  • AS n+1 /AS n may be used, instead of S n /S n ⁇ 1 , as the period ratio.
  • the quantization step conversion factor ⁇ n+1 in the (n+1) period can be calculated by substituting the ratio between the target setting bit rate T n+1 in the (n+1) period and the average period bit rate AS n+1 of past M periods including the (n+1) period into the function f.
  • the average period bit rate AC n from the (n ⁇ M+1) period to the n period may be used instead of the average output bit rate C n in the n period.
  • AC n may be used instead of C n . This makes it possible to more gently control the target setting bit rate T n+1 .
  • the rate control method (D) will be discussed. Also in the rate control method (D), like in the rate control method (C), the target setting bit rate T n+1 of the second stream in the (n+1) period is determined at the point of time when the n period is finished, and by using the determined target setting bit rate T n+1 , the quantization step conversion factor ⁇ n+1 in the (n+1) period is calculated. In the rate control method (D), the method of determining the target setting bit rate T n+1 of the second stream in the (n+1) period is different from that of the rate control method (C).
  • Eq. 24 is an equation for calculation of the target setting bit rate T n+1 in the (n+1) period.
  • the value obtained by subtracting the average output bit rate C n of the converted second stream in the n period from the target setting bit rate T n in the n period is used as the target difference.
  • the target difference is adjusted, however, by multiplying the target difference by the period ratio in the rate control method (C), the target difference is multiplied by a period difference in the rate control method (D), as shown in Eq. 24.
  • T n+1 T+k *( S n ⁇ S n ⁇ 1 )*( T n ⁇ C n ) (Eq.24)
  • the target difference is multiplied by (S n ⁇ S n ⁇ 1 ).
  • This multiplier factor (S n ⁇ S n ⁇ 1 ) is the period difference obtained by subtracting the average input bit rate S n ⁇ 1 of the first stream in the (n ⁇ 1) period from the average input bit rate S n of the first stream in the n period. Multiplying the target difference by the period difference can adjust the target difference.
  • the factor “k” is a positive factor for adjusting the target setting bit rate T n+1 .
  • multiplying the target difference by the period difference can correct the local variation of the target difference. For example, if the average input bit rate S n gradually becomes smaller, sometimes the average output bit rate C n accordingly becomes smaller and target difference (T n ⁇ C n ) becomes a positive value. Also in such a case, the period difference (S n ⁇ S n ⁇ 1 ) becomes a negative value, to thereby make such a correction that the target setting bit rate T n+1 should not be set larger. In other words, if the average input bit rate S n becomes smaller, contrary to this variation, the target setting bit rate T n+1 is controlled not to become larger.
  • the target difference (T n ⁇ C n ) is multiplied by the period difference.
  • the period difference may be added to the target difference.
  • “h” is a positive factor for adjusting the target setting bit rate T n+1 .
  • T n+1 T+h *( S n ⁇ S n ⁇ 1 )+ k *( T n ⁇ C n ) (Eq.25)
  • the value obtained by subtracting the average input bit rate S n ⁇ 1 of the first stream in the (n ⁇ 1) period from the average input bit rate S n of the first stream in the n period is used as the period difference. Then, the target difference is multiplied by the period difference.
  • the average input bit rate S n+1 of the first stream in the (n+1) period can be prefetched.
  • the average input bit rate S n+1 may be used. In this case, in Eq. 24, (S n+1 ⁇ S n ) is used, instead of (S n ⁇ S n ⁇ 1 ), as the period difference.
  • the average input bit rate S n+1 of the first stream in the (n+1) period it is possible to control the target setting bit rate T n+1 with higher precision.
  • the value obtained by subtracting the average input bit rate S n ⁇ 1 of the first stream in the (n ⁇ 1) period from the average input bit rate S n of the first stream in the n period is used as the period difference. Then, the period difference is added to the target difference.
  • the average input bit rate S n+1 may be used. In this case, in Eq. 25, (S n+1 ⁇ S n ) is used, instead of (S n ⁇ S n ⁇ 1 ), as the period difference.
  • the average input bit rate S n+1 of the first stream in the (n+1) period it is possible to control the target setting bit rate T n+1 with higher precision.
  • the quantization step conversion factor ⁇ n+1 in the (n+1) period can be calculated by substituting the ratio between the target setting bit rate T n+1 in the (n+1) period and the average input bit rate S n+1 in the (n+1) period into the function f.
  • (S n ⁇ S n ⁇ 1 ) is used as the period difference.
  • the difference between the average period bit rate AS n of past M periods including the n period and the average period bit rate AS n ⁇ 1 of past M periods including the (n ⁇ 1) period may be used as the period difference.
  • (AS n ⁇ AS n ⁇ 1 ) may be used, instead of (S n ⁇ S n ⁇ 1 ), as the period difference. With this, it is possible to decrease the effect of local variation and optimally control the target setting bit rate T n+1 .
  • the ratio between the average period bit rate AS n+1 of past M periods including the (n+1) period and the average period bit rate AS n of past M periods including the n period may be used as the period difference.
  • (AS n+1 ⁇ As n ) may be used, instead of (S n ⁇ S n ⁇ 1 ), as the period difference.
  • the quantization step conversion factor ⁇ n+1 in the (n+1) period can be calculated by substituting the ratio between the target setting bit rate T n+1 in the (n+1) period and the average period bit rate AS n+1 of past M periods including the (n+1) period into the function f.
  • the average period bit rate AC n from the (n ⁇ M+1) period to the n period may be used instead of the average output bit rate C n in the n period.
  • AC n may be used instead of C n . This makes it possible to more gently control the target setting bit rate T n+1 .
  • the average input bit rate S n in the control unit time L n is used in the process of calculating the quantization step value Q.
  • the average input bit rate S n ⁇ 1 or S n+1 in the control unit time L n ⁇ 1 or L n+1 is used.
  • the average period bit rate AS n or the like is used.
  • one GOP period is used basically as the control unit time L n . If the number of frames in one GOP is small or the ratio of I picture frames in one GOP is high, however, there is a possibility that the average input bit rate S n may become high sharply. Then, in such a case, the transcoder 1 of the preferred embodiments corrects the control unit time L n to reduce variation of the average input bit rate S n .
  • the decoder 2 first, acquires the number of frames included in an inputted GOP. Then, if the number of frames included in the GOP is not less than a predetermined threshold value, it is determined, with respect to the GOP, that one GOP serves as a control unit time L n . On the other hand, if the number of frames included in the GOP is less than the predetermined threshold value, the GOP is connected to the following GOP so that the number of frames included in the two connected GOPs can become not less than the predetermined threshold value. If the number of frames included in the two connected GOPs is less than the predetermined threshold value, the following GOP is further connected to the connected GOPs. Thus, the GOPs are connected to one another until the number of frames included in the connected GOPs becomes not less than the predetermined threshold value and it is determined that the connected GOPs serve as one control unit time.
  • FIGS. 3A and 3B to 6 A and 6 B show cases where the GOPs of the input streams are in a one-to-one correspondence with the control unit times.
  • the lower FIGS. 3B , 4 B, 5 B and 6 B show cases where the control unit times are corrected by using the methods of determining the control unit times of the first preferred embodiment after the input streams having the same picture structures as those in the respective upper figures are inputted.
  • the threshold value of the number of frames is set to 15. Specifically, if the number of frames in the GOP is less than 15, GOPs are connected until the number of frames becomes not less than 15, to correct the control unit time.
  • each of the GOP 1 to the GOP 3 consists of 15 frames. Specifically, each of the GOP 1 to the GOP 3 has a basic picture structure “IBBPBBPBBPBBPBB”. Therefore, both in FIGS. 3A and 3B , the GOP 1 to the GOP 3 correspond to the control unit times L 1 to L 3 , respectively. In other words, in this case, the control unit time is a unit of one GOP and not corrected.
  • the GOP 1 and the GOP 4 each have the basic picture structure “IBBPBBPBBPBBPBB”, consisting of 15 frames.
  • the GOP 2 has a picture structure “IBB” and the number of frames is 3.
  • the GOP 3 has a picture structure “IBBPBBPBBPBB” and the number of frames is 12.
  • the GOP 1 to the GOP 4 correspond to the control unit times L 1 to L 4 , respectively, like in FIG. 4A , the respective values of the average input bit rates S 2 and S 3 of the control unit times L 2 and L 3 become high sharply. Then, as shown in FIG. 4B , the GOP 2 and the GOP 3 are connected to each other, to determine one control unit time L 2 . With this connection, the number of frames in the control unit time L 2 becomes 15 and the variation of the average input bit rate S n can be reduced to be smaller.
  • the GOP 1 , the GOP 3 and the GOP 4 each have the basic picture structure “IBBPBBPBBPBBPBB”, consisting of 15 frames.
  • the GOP 2 has a picture structure “IBB” and the number of frames is 3.
  • the GOP 1 to the GOP 4 correspond to the control unit times L 1 to L 4 , respectively, like in FIG. 5A , the value of the average input bit rate S 2 of the control unit time L 2 becomes high sharply.
  • the GOP 2 and the GOP 3 are connected to each other, to determine one control unit time L 2 .
  • the number of frames in the control unit time L 2 becomes 18 and the variation of the average input bit rate S n can be reduced to be smaller.
  • the GOP 3 is 15 and the condition for the control unit time is satisfied, since the number of frames in the GOP 2 is smaller, the GOP 3 is connected to the GOP 2 , to correct the control unit time.
  • the number of frames in the control unit time L 2 becomes 18, which is larger than the number of frames in other control unit times, there is no problem in terms of reduction of the variation of the average input bit rate S n .
  • the GOP 1 has the basic picture structure “IBBPBBPBBPBBPBB”, consisting of 15 frames.
  • the GOP 2 has a picture structure “IBB” and the number of frames is 3.
  • the GOP 3 has a picture structure “IBBPBBPBB” and the number of frames is 9, and the GOP 4 has a picture structure “IBBPBBPBBPBBPBBPBB” and the number of frames is 18.
  • the GOP 1 to the GOP 4 correspond to the control unit times L 1 to L 4 , respectively, like in FIG. 6A , the respective values of the average input bit rates S 2 and S 3 of the control unit times L 2 and L 3 become high sharply.
  • the GOP 2 , the GOP 3 and the GOP 4 are connected to one another, to determine one control unit time L 2 .
  • the number of frames in the control unit time L 2 becomes 30 and the variation of the average input bit rate S n can be reduced to be smaller.
  • the following GOP is further connected thereto, to thereby reduce the variation of the average input bit rate S n .
  • control unit times may be corrected on a frame basis.
  • control unit time is corrected adaptively in accordance with the number of frames included in the GOPs of the input stream. This can reduce the variation of the average input bit rate S n , and with the constant average input bit rate S n , it is possible to perform an optimal rate control.
  • the decoder 2 first, acquires the number of I picture frames included in an inputted GOP. Then, if the ratio of the I picture frames included in the GOP is not more than a predetermined threshold value, it is determined, with respect to the GOP, that one GOP serves as a control unit time L n . On the other hand, if the ratio of the I picture frames included in the GOP exceeds the predetermined threshold value, the GOP is connected to the following GOP so that the ratio of the I picture frames included in the two connected GOPs can become not more than the predetermined threshold value. If the ratio of the I picture frames included in the two connected GOPs exceeds the predetermined threshold value, the following GOP is further connected to the connected GOPs. Thus, the GOPs are connected to one another until the ratio of the I picture frames included in the connected GOPs becomes not more than the predetermined threshold value and it is determined that the connected GOPs serve as one control unit time.
  • FIGS. 7A and 7B to 10 A and 10 B show cases where the GOPs of the input streams are in a one-to-one correspondence with the control unit times.
  • the lower FIGS. 7B , 8 B, 9 B and 10 B show cases where the control unit times are corrected by using the methods of determining the control unit times of the second preferred embodiment after the input streams having the same picture structures as those in the respective upper figures are inputted.
  • the threshold value of the ratio of I picture frames is set to 0.2. Specifically, if the ratio of the I picture frames included in the GOP exceeds 0.2, GOPs are connected until the ratio of the I picture frames becomes not more than 0.2, to correct the control unit time.
  • each of the GOP 1 to the GOP 3 consists of 15 frames and each of the GOP 1 to the GOP 3 has a picture structure “IBBPBBPBBPBBPBB”.
  • the ratio of the I picture frames is 1/15 ⁇ 0.07. Therefore, both in FIGS. 7A and 7B , the GOP 1 to the GOP 3 correspond to the control unit times L 1 to L 3 , respectively. In other words, in this case, the control unit time is a unit of one GOP and not corrected.
  • the GOP 1 and the GOP 4 each have the basic picture structure “IBBPBBPBBPBBPBB”, consisting of 15 frames, and the ratio of the I picture frames is 1/15 ⁇ 0.07.
  • the GOP 2 has a picture structure “III” and the number of frames is 3.
  • the GOP 3 has a picture structure “IBBPBBPBBPBB” and the number of frames is 12.
  • the value of the average input bit rate S 2 of the control unit time L 2 becomes high sharply.
  • the GOP 2 , the GOP 3 and the GOP 4 are connected to one another, to determine one control unit time L 2 .
  • the ratio of the I picture frames is 4/15 ⁇ 0.27, exceeding the threshold value of 0.2.
  • the number of frames in the control unit time L 2 becomes 30 and the ratio of the I picture frames becomes 5/30 ⁇ 0.17. This reduces the variation of the average input bit rate S n to be smaller.
  • the GOP 1 and the GOP 4 each have the basic picture structure “IBBPBBPBBPBBPBB”, consisting of 15 frames.
  • the GOP 2 has a picture structure “IPPIPP” and the ratio of the I picture frames is 2/6 ⁇ 0.33.
  • the GOP 3 has a picture structure “IBBPBBPBBPBB”.
  • the GOP 1 to the GOP 4 correspond to the control unit times L 1 to L 4 , respectively, like in FIG. 9A , the value of the average input bit rate S 2 of the control unit time L 2 becomes high sharply. Then, as shown in FIG. 9B , the GOP 2 and the GOP 3 are connected to each other, to determine one control unit time L 2 . With this connection, the ratio of the I picture frames in the control unit time L 2 becomes 3/18 ⁇ 0.17 and the variation of the average input bit rate S n can be reduced to be smaller.
  • the GOP 1 and the GOP 4 each have the basic picture structure “IBBPBBPBBPBBPBB”, consisting of 15 frames.
  • the GOP 2 has a picture structure “IPPPPP” and the ratio of the I picture frames is 1/6 ⁇ 0.17, not more than the threshold value of 0.2.
  • the GOP 3 has a picture structure “IBBPBBPBB” and the ratio of the I picture frames is not more than 0.2. Therefore, both in FIGS. 10A and 10B , the GOP 1 to the GOP 4 correspond to the control unit times L 1 to L 4 , respectively.
  • the threshold value of the second preferred embodiment is only one example. In accordance with the bit rate of the input stream or the picture structure, an optimal value may be selected as appropriate. Though the case where the control unit times are connected on a GOP basis has been discussed in the second preferred embodiment, the control unit times may be corrected on a frame basis.
  • control unit time is corrected adaptively in accordance with the ratio of the I picture frames included in the GOP of the input stream. This can reduce the variation of the average input bit rate S n , and with the constant average input bit rate S n , it is possible to perform an optimal rate control.
  • the number of I picture frames relative to the number of all frames included in the GOP is the ratio of the I picture frames.
  • respective weighted numbers are obtained by multiplying the respective numbers of I, P and B picture frames constituting the GOP by the bit ratio and the ratio of the I picture frames is obtained by using these weighted numbers.
  • the threshold value has only to be set to any value larger than 0.2 which is used in the second preferred embodiment. For example, any value in a range from 0.22 to 0.24 may be used.
  • the ratio of the I picture frames in the GOP 2 is 1/6 ⁇ 0.17, which satisfies the condition for the control unit time in the second preferred embodiment.
  • the weighted ratio of the I picture frames is 10/42 ⁇ 0.24.
  • the threshold value is 0.24, correction is made with the period made by connection of the GOP 2 and the GOP 3 as the control unit time. If the threshold value is less than 0.24, the GOP 4 is further connected thereto.

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CN108235059A (zh) * 2018-03-09 2018-06-29 网宿科技股份有限公司 一种分配转码任务的方法和系统

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US8817890B2 (en) * 2006-02-01 2014-08-26 Verint Systems Inc. System and method for controlling the long term generation rate of compressed data
US20110075731A1 (en) * 2008-06-02 2011-03-31 Megachips Corporation Transcoder
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CN108600758A (zh) * 2018-03-26 2018-09-28 南京地铁建设有限责任公司 基于城市轨道乘客信息系统的i帧高突发码流整形方法
CN110913245A (zh) * 2019-11-08 2020-03-24 网宿科技股份有限公司 一种控制视频转码码率的方法和装置

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Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:HASEGAWA, HIROMU;TAKASU, NOBUYUKI;SAITO, MAKOTO;REEL/FRAME:022163/0971

Effective date: 20090109

STCB Information on status: application discontinuation

Free format text: ABANDONED -- FAILURE TO RESPOND TO AN OFFICE ACTION