INTERNATIONAL TELECOMMUNICATION UNION
`
`ITU-T
`
`TELECOMMUNICATION
`STANDARDIZATION SECTOR
`OF ITU
`
`H.263
`(03/96)
`
`TRANSMISSION OF NON-TELEPHONE SIGNALS
`
`VIDEO CODING
`FOR LOW BIT RATE COMMUNICATION
`
`ITU-T Recommendation H.263
`
`(Previously “CCITT Recommendation”)
`
`Realtime Adaptive Streaming LLC
`Exhibit 2010
`IPR2019-01035
`Page 1
`
`

`

`FOREWORD
`
`The ITU-T (Telecommunication Standardization Sector) is a permanent organ of the International Telecommunication
`Union (ITU). The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommen-
`dations on them with a view to standardizing telecommunications on a worldwide basis.
`
`The World Telecommunication Standardization Conference (WTSC), which meets every four years, establishes the
`topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics.
`
`The approval of Recommendations by the Members of the ITU-T is covered by the procedure laid down in WTSC
`Resolution No. 1 (Helsinki, March 1-12, 1993).
`
`ITU-T Recommendation H.263 was prepared by ITU-T Study Group 15 (1993-1996) and was approved under the
`WTSC Resolution No. 1 procedure on the 19 th of March 1996.
`
`___________________
`
`In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication
`administration and a recognized operating agency.
`
`NOTE
`
`All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or
`mechanical, including photocopying and microfilm, without permission in writing from the ITU.
`
` ITU 1996
`
`Realtime Adaptive Streaming LLC
`Exhibit 2010
`IPR2019-01035
`Page 2
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`

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`Recommendation H.263 (03/96)
`
`CONTENTS
`
`1
`2
`3
`
`4
`
`Scope..............................................................................................................................................................
`References......................................................................................................................................................
`Brief specification ..........................................................................................................................................
`3.1
`Video input and output .....................................................................................................................
`3.2
`Digital output and input....................................................................................................................
`3.3
`Sampling frequency..........................................................................................................................
`3.4
`Source coding algorithm...................................................................................................................
`3.5
`Bit rate ..............................................................................................................................................
`3.6
`Buffering...........................................................................................................................................
`3.7
`Symmetry of transmission ................................................................................................................
`3.8
`Error handling...................................................................................................................................
`3.9
`Multipoint operation .........................................................................................................................
`Source coder...................................................................................................................................................
`4.1
`Source format....................................................................................................................................
`4.2
`Video source coding algorithm.........................................................................................................
`4.3
`Coding control ..................................................................................................................................
`4.4
`Forced updating ................................................................................................................................
`4.5
`Byte alignment of start codes............................................................................................................
`Syntax and semantics .....................................................................................................................................
`5.1
`Picture layer......................................................................................................................................
`5.2
`Group of Blocks Layer .....................................................................................................................
`5.3
`Macroblock Layer.............................................................................................................................
`5.4
`Block Layer ......................................................................................................................................
`Decoding process ...........................................................................................................................................
`6.1
`Motion compensation .......................................................................................................................
`6.2
`Coefficients decoding .......................................................................................................................
`6.3
`Reconstruction of blocks ..................................................................................................................
`Annex A – Inverse transform accuracy specification................................................................................................
`Annex B – Hypothetical Reference Decoder ............................................................................................................
`Annex C – Considerations for Multipoint .................................................................................................................
`C.1
`Freeze picture request.......................................................................................................................
`C.2
`Fast update request ...........................................................................................................................
`C.3
`Freeze picture release........................................................................................................................
`Continuous Presence Multipoint (CPM) (not used for Recommendation H.324)............................
`C.4
`Annex D – Unrestricted Motion Vector mode ..........................................................................................................
`Motion vectors over picture boundaries ...........................................................................................
`D.1
`Extension of the motion vector range...............................................................................................
`D.2
`Annex E – Syntax-based Arithmetic Coding mode...................................................................................................
`E.1
`Introduction ......................................................................................................................................
`Specification of SAC encoder...........................................................................................................
`E.2
`Specification of SAC decoder...........................................................................................................
`E.3
`E.4
`Syntax ...............................................................................................................................................
`
`5
`
`6
`
`Page
`1
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`5
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`8
`8
`8
`9
`12
`13
`18
`18
`18
`24
`25
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`Recommendation H.263 (03/96)
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`PSC_FIFO ........................................................................................................................................
`E.5
`Fixed length symbols........................................................................................................................
`E.6
`Non-fixed length symbols.................................................................................................................
`E.7
`SAC Models......................................................................................................................................
`E.8
`Annex F – Advanced Prediction mode......................................................................................................................
`F.1
`Introduction ......................................................................................................................................
`F.2
`Four motion vectors per macroblock ................................................................................................
`Overlapped motion compensation for luminance .............................................................................
`F.3
`Annex G – PB-frames mode......................................................................................................................................
`G.1
`Introduction ......................................................................................................................................
`G.2
`PB-frames and INTRA blocks..........................................................................................................
`G.3
`Block Layer ......................................................................................................................................
`G.4
`Calculation of vectors for the B-picture in a PB-frame ....................................................................
`Prediction of a B-block in a PB-frame..............................................................................................
`G.5
`Annex H – Forward Error Correction for coded video signal...................................................................................
`H.1
`Introduction ......................................................................................................................................
`Error correction framing ...................................................................................................................
`H.2
`H.3
`Error correcting code ........................................................................................................................
`H.4
`Relock time for error corrector framing............................................................................................
`
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`ii
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`Recommendation H.263 (03/96)
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`IPR2019-01035
`Page 4
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`SUMMARY
`
`This Recommendation specifies a coded representation that can be used for compressing the moving picture component
`of audio-visual services at low bit rates. The basic configuration of the video source coding algorithm is based on
`Recommendation H.261 and is a hybrid of inter-picture prediction to utilize temporal redundancy and transform coding
`of the remaining signal to reduce spatial redundancy. The source coder can operate on five standardised picture formats:
`sub-QCIF, QCIF, CIF, 4CIF and 16CIF.
`The decoder has motion compensation capability, allowing optional incorporation of this technique in the coder. Half
`pixel precision is used for the motion compensation, as opposed to Recommendation H.261 where full pixel precision
`and a loopfilter are used. Variable length coding is used for the symbols to be transmitted.
`In addition to the basic video source coding algorithm, four negotiable coding options are included for improved
`performance: Unrestricted Motion Vectors, Syntax-based Arithmetic Coding, Advanced Prediction and PB-frames. All
`these options can be used together or separately.
`
`Recommendation H.263 (03/96)
`
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`IPR2019-01035
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`Realtime Adaptive Streaming LLC
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`

`

`Recommendation H.263
`
`Recommendation H.263 (03/96)
`
`VIDEO CODING FOR LOW BIT RATE COMMUNICATION
`
`(Geneva, 1996)
`
`1
`
`Scope
`
`This Recommendation specifies a coded representation that can be used for compressing the moving picture component
`of audio-visual services at low bit rates. The basic configuration of the video source coding algorithm is based on
`Recommendation H.261. Four negotiable coding options are included for improved performance.
`
`2
`
`References
`
`The following Recommendations and other references contain provisions which, through reference in this text, constitute
`provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations
`and other references are subject to revision; all users of this Recommendation are therefore encouraged to investigate the
`possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the
`currently valid ITU-T Recommendations is regularly published.
`
`[1]
`
`[2]
`
`[3]
`
`[4]
`
`[5]
`
`[6]
`
`[7]
`
`3
`
`ITU-T Recommendation H.223 (1996), Multiplexing protocol for low bit rate multimedia communication.
`
`ITU-T Recommendation H.242 (1996), System for establishing communication between audiovisual terminals
`using digital channels up to 2 Mbit/s.
`
`ITU-T Recommendation H.245 (1996), Control protocol for multimedia communication.
`ITU-T Recommendation H.261 (1993), Video codec for audiovisual services at p × 64 kbit/s.
`
`ITU-T Rec. H.262 (1995) | ISO/IEC 13818-2:1995, Information technology – Generic coding of moving pictures
`and associated audio information: video.
`
`ITU-T Recommendation H.320 (1996), Narrow-band visual telephone systems and terminal equipment.
`
`ITU-T Recommendation H.324 (1996), Terminal for low bit rate multimedia communication.
`
`Brief specification
`
`An outline block diagram of the codec is given in Figure 1.
`
`3.1
`
`Video input and output
`
`To permit a single Recommendation to cover use in and between regions using 625- and 525-line television standards,
`the source coder operates on pictures based on a Common Intermediate Format (CIF). The standards of the input and
`output television signals, which may, for example, be composite or component, analogue or digital and the methods of
`performing any necessary conversion to and from the source coding format are not subject to recommendation.
`
`3.2
`
`Digital output and input
`
`The video coder provides a self-contained digital bit stream which may be combined with other multi-facility signals (for
`example as defined in Recommendation H.223). The video decoder performs the reverse process.
`
`3.3
`
`Sampling frequency
`
`Pictures are sampled at an integer multiple of the video line rate. This sampling clock and the digital network clock are
`asynchronous.
`
`
`
`
`
`Recommendation H.263 (03/96)
`
`1
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`External control
`
`Coding control
`
`Video
`signal
`
`Source
`coder
`
`Source
`decoder
`
`Video multiplex
`coder
`
`a) Video coder
`
`Video multiplex
`decoder
`
`b) Video decoder
`
`Transmission
`buffer
`
`Receiving
`buffer
`
`Coded
`bit stream
`
`T1520800-96/d01
`
`FIGURE 1/H.263
`Outline block diagram of the video codec
`
`
`
`FIGURE 1/H.263...[D01] = 3 CM (118%)
`
`3.4
`
`Source coding algorithm
`
`A hybrid of inter-picture prediction to utilize temporal redundancy and transform coding of the remaining signal to
`reduce spatial redundancy is adopted. The decoder has motion compensation capability, allowing optional
`incorporation of this technique in the coder. Half pixel precision is used for the motion compensation, as opposed to
`Recommendation H.261 where full pixel precision and a loopfilter are used. Variable length coding is used for the
`symbols to be transmitted.
`
`In addition to the core H.263 coding algorithm, four negotiable coding options are included that will be described in the
`subsequent subclauses. All these options can be used together or separately.
`
`3.4.1
`
`Unrestricted Motion Vector mode
`
`In this optional mode motion vectors are allowed to point outside the picture. The edge pixels are used as prediction for
`the “not existing” pixels. With this mode a significant gain is achieved if there is movement across the edges of the
`picture, especially for the smaller picture formats (see also Annex D). Additionally, this mode includes an extension of
`the motion vector range so that larger motion vectors can be used. This is especially useful in case of camera movement.
`
`3.4.2
`
`Syntax-based Arithmetic Coding mode
`
`In this optional mode arithmetic coding is used instead of variable length coding. The SNR and reconstructed pictures
`will be the same, but significantly fewer bits will be produced (see also Annex E).
`
`3.4.3
`
`Advanced Prediction mode
`
`In this optional mode Overlapped Block Motion Compensation (OBMC) is used for the luminance part of P-pictures
`(see also Annex F). Four 8 × 8 vectors instead of one 16 × 16 vector are used for some of the macroblocks in the picture.
`The encoder has to decide which type of vectors to use. Four vectors use more bits, but give better prediction. The use of
`this mode generally gives a considerable improvement. Especially a subjective gain is achieved because OBMC results
`in less blocking artifacts.
`
`2
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`3.4.4
`
`PB-frames mode
`
`A PB-frame consists of two pictures being coded as one unit. The name PB comes from the name of picture types in
`Recommendation H.262 where there are P-pictures and B-pictures. Thus a PB-frame consists of one P-picture which is
`predicted from the previous decoded P-picture and one B-picture which is predicted from both the previous decoded
`P-picture and the P-picture currently being decoded. The name B-picture was chosen because parts of B-pictures may be
`bidirectionally predicted from the past and future pictures. With this coding option, the picture rate can be increased
`considerably without increasing the bit rate much.
`
`3.5
`
`Bit rate
`
`The transmission clock is provided externally. The video bit rate may be variable. In this Recommendation no
`constraints on the video bit rate are given; constraints will be given by the terminal or the network.
`
`3.6
`
`Buffering
`
`The encoder shall control its output bit stream to comply with the requirements of the hypothetical reference decoder
`defined in Annex B. Video data shall be provided on every valid clock cycle. This can be ensured by MCBPC stuffing
`(see Tables 4 and 5) or, when forward error correction is used, also by forward error correction stuffing frames (see
`Annex H).
`
`The number of bits created by coding any single picture shall not exceed a maximum value specified by the parameter
`BPPmaxKb which is measured in units of 1024 bits. The minimum allowable value of the BPPmaxKb parameter
`depends on the largest source picture format that has been negotiated for use in the bit stream (see Table 1). An encoder
`may use a larger value for BPPmaxKb than as specified in Table 1, provided the larger value is first negotiated by
`external means, for example Recommendation H.245.
`
`TABLE 1/H.263
`
`BPPmaxKb for each of the source picture formats
`
`
`
`Source format
`
`sub-QCIF
`
`QCIF
`
`CIF
`
`4CIF
`
`16CIF
`
`BPPmaxKb
`
`64
`
`64
`
`256
`
`512
`
`1024
`
`
`
`
`
`3.7
`
`Symmetry of transmission
`
`The codec may be used for bidirectional or unidirectional visual communication.
`
`3.8
`
`Error handling
`
`Error handling should be provided by external means (for example Recommendation H.223). If it is not provided by
`external means (for example in Recommendation H.221) the optional error correction code and framing as described in
`Annex H can be used.
`
`A decoder can send a command to encode one or more GOBs of its next picture in INTRA mode with coding parameters
`such as to avoid buffer overflow. A decoder can also send a command to transmit only non-empty GOB headers. The
`transmission method for these signals is by external means (for example Recommendation H.245).
`
`
`
`
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`Recommendation H.263 (03/96)
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`3
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`3.9
`
`Multipoint operation
`
`Features necessary to support switched multipoint operation are included in Annex C.
`
`4
`
`Source coder
`
`4.1
`
`Source format
`
`The source coder operates on non-interlaced pictures occurring 30 000/1001 (approximately 29.97) times per second.
`The tolerance on picture frequency is ± 50 ppm.
`
`Pictures are coded as luminance and two colour difference components (Y, CB and CR). These components and the
`codes representing their sampled values are as defined in ITU-R Recommendation 601.
`
`• Black = 16;
`
`• White = 235;
`
`•
`
`•
`
`Zero colour difference = 128;
`
`Peak colour difference = 16 and 240.
`
`These values are nominal ones and the coding algorithm functions with input values of 1 through to 254.
`
`There are five standardised picture formats: sub-QCIF, QCIF, CIF, 4CIF and 16CIF. For each of these picture formats,
`the luminance sampling structure is dx pixels per line, dy lines per picture in an orthogonal arrangement. Sampling of
`each of the two colour difference components is at dx/2 pixels per line, dy/2 lines per picture, orthogonal. The values of
`dx, dy, dx/2 and dy/2 are given in Table 2 for each of the picture formats.
`
`TABLE 2/H.263
`
`Number of pixels per line and number of lines for each of the H.263 picture formats
`
`Number of pixels
`for luminance
`(dx)
`
`Number of lines
`for luminance
`(dy)
`
`Number of pixels
`for chrominance
`(dx/2)
`
`Number of lines
`for chrominance
`(dy/2)
`
`128
`
`176
`
`352
`
`704
`
`1408
`
`96
`
`144
`
`288
`
`576
`
`1152
`
`64
`
`88
`
`176
`
`352
`
`704
`
`48
`
`72
`
`144
`
`288
`
`576
`
`
`Picture Format
`
`sub-QCIF
`
`QCIF
`
`CIF
`
`4CIF
`
`16CIF
`
`
`
`
`
`For each of the picture formats, colour difference samples are sited such that their block boundaries coincide with
`luminance block boundaries as shown in Figure 2. The pixel aspect ratio is the same for each of these picture formats
`and is the same as defined for QCIF and CIF in Recommendation H.261: (4/3) * (288/352). The picture area covered by
`all picture formats except the sub-QCIF picture format has an aspect ratio of 4:3.
`
`4
`
`Recommendation H.263 (03/96)
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`T1519560-95/d02
`
`Luminance sample
`
`Chrominance sample
`
`Block edge
`
`FIGURE 2/H.263
`Positioning of luminance and chrominance samples
`
`FIGURE 2/H.263...[D02] = 3 CM (118%)
`
`All decoders shall be able to operate using sub-QCIF. All decoders shall also be able to operate using QCIF. Some
`decoders may also operate with CIF, 4CIF or 16CIF. Encoders shall be able to operate with one of the formats sub-QCIF
`and QCIF. The encoders determine which of these two formats are used, and are not obliged to be able to operate with
`both. Some encoders can also operate with CIF, 4CIF or 16CIF. Which formats can be handled by the decoder is
`signalled by external means, for example Recommendation H.245. For a complete overview of possible picture formats
`and video coding algorithms, refer to the terminal description, for example Recommendation H.324.
`
`NOTE – For CIF, the number of pixels per line is compatible with sampling the active portions of the luminance and
`colour difference signals from 525- or 625-line sources at 6.75 and 3.375 MHz respectively. These frequencies have a simple
`relationship to those in ITU-R Recommendation 601.
`
`Means shall be provided to restrict the maximum picture rate of encoders by having a minimum number of
`non-transmitted pictures between transmitted ones. Selection of this minimum number shall be by external means (for
`example, Recommendation H.245). For the calculation of the minimum number of non-transmitted pictures in PB-
`frames mode, the P-picture and the B-picture of a PB-frames unit are taken as two separate pictures.
`
`4.2
`
`Video source coding algorithm
`
`The source coder is shown in generalized form in Figure 3. The main elements are prediction, block transformation and
`quantization.
`
`4.2.1
`
`GOBs, macroblocks and blocks
`
`Each picture is divided into groups of blocks (GOBs). A Group of Blocks (GOB) comprises of k * 16 lines, depending
`on the picture format (k = 1 for sub-QCIF, QCIF and CIF; k = 2 for 4CIF; k = 4 for 16CIF). The number of GOBs per
`picture is 6 for sub-QCIF, 9 for QCIF, and 18 for CIF, 4CIF and 16CIF. The GOB numbering is done by use of vertical
`scan of the GOBs, starting with the upper GOB (number 0) and ending with the lower GOB. An example of the
`arrangement of GOBs in a picture is given for the CIF picture format in Figure 4. Data for each GOB consists of a GOB
`header (may be empty) followed by data for macroblocks. Data for GOBs is transmitted per GOB in increasing GOB
`number.
`
`
`
`
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`Recommendation H.263 (03/96)
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`5
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`To video
`multiplex
`coder
`
`p t q
`
`z
`
`q
`
`v
`
`T1519570-95/d03
`
`Transform
`Quantizer
`Picture memory with motion compensated variable delay
`Coding Control
`Flag for INTRA/INTER
`Flag for transmitted or not
`Quantizer indication
`Quantizing index for transform coefficients
`Motion vector
`
`CC
`
`T
`
`Video
`in
`
`Q–1
`
`T–1
`
`Q
`
`P
`
`TQPC
`
`C
`
`ptq
`
`z
`
`qv
`
`FIGURE 3/H.263
`Source coder
`
`
`
`FIGURE 3/H.263...[D03] = 3 CM (118%)
`
`Each GOB is divided into macroblocks. A macroblock relates to 16 pixels by 16 lines of Y and the spatially
`corresponding 8 pixels by 8 lines of CB and CR. Further, a macroblock consists of four luminance blocks and the two
`spatially corresponding colour difference blocks as shown in Figure 5. Each luminance or chrominance block relates to
`8 pixels by 8 lines of Y, CB or CR. A GOB comprises one macroblock row for sub-QCIF, QCIF and CIF, two
`macroblock rows for 4CIF and four macroblock rows for 16CIF.
`
`The macroblock numbering is done by use of horizontal scan of the macroblock rows from left to right, starting with the
`upper macroblock row and ending with the lower macroblock row. Data for the macroblocks is transmitted per
`macroblock in increasing macroblock number. Data for the blocks is transmitted per block in increasing block number
`(see Figure 5).
`
`The criteria for choice of mode and transmitting a block are not subject to recommendation and may be varied
`dynamically as part of the coding control strategy. Transmitted blocks are transformed and resulting coefficients are
`quantized and entropy coded.
`
`4.2.2
`
`Prediction
`
`The prediction is inter-picture and may be augmented by motion compensation (see 4.2.3). The coding mode in which
`prediction is applied is called INTER; the coding mode is called INTRA if no prediction is applied. The INTRA coding
`mode can be signalled at the picture level (INTRA for I-pictures or INTER for P-pictures) or at the macroblock level in
`P-pictures. In the optional PB-frames, mode B-pictures are always coded in INTER mode. The B-pictures are partly
`predicted bidirectionally (refer to Annex G).
`
`6
`
`Recommendation H.263 (03/96)
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`FIGURE 4/H.263
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`Arrangement of Group of Blocks in a CIF picture
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`1
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`3
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`2
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`4
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`Y
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`5
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`CB
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`6
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`CR
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`FIGURE 5/H.263
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`Arrangement of blocks in a macroblock
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`4.2.3 Motion compensation
`The decoder will accept one vector per macroblock or if the Advanced Prediction mode is used, one or four vectors per
`macroblock (see Annex F). If the PB-frames mode is used, one additional delta vector can be transmitted per macroblock
`for adaptation of the motion vectors for prediction of the B-macroblock.
`Both horizontal and vertical components of the motion vectors have integer or half integer values. In the default
`prediction mode, these values are restricted to the range [–16, 15.5] (this is also valid for the forward and backward
`motion vector components for B-pictures). In the Unrestricted Motion Vector mode however, the maximum range for
`vector components is [–31.5, 31.5], with the restriction that only values that are within a range of [–16, 15.5] around the
`predictor for each motion vector component can be reached if the predictor is in the range [–15.5, 16]. If the predictor is
`outside [–15.5, 16], all values within the range [–31.5, 31.5] with the same sign as the predictor plus the zero value can
`be reached (see also Annex D).
`A positive value of the horizontal or vertical component of the motion vector signifies that the prediction is formed from
`pixels in the referenced picture which are spatially to the right or below the pixels being predicted.
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`Recommendation H.263 (03/96)
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`7
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`Realtime Adaptive Streaming LLC
`Exhibit 2010
`IPR2019-01035
`Page 13
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`

`

`Motion vectors are restricted such that all pixels referenced by them are within the coded picture area, except when the
`Unrestricted Motion Vector mode and/or the Advanced Prediction mode is used (see Annexes D and F).
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`4.2.4
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`Quantization
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`The number of quantizers is 1 for the first coefficient of INTRA blocks and 31 for all other coefficients. Within a
`macroblock the same quantizer is used for all coefficients except the first one of INTRA blocks. The decision levels are
`not defined. The first coefficient of INTRA blocks is nominally the transform dc value uniformly quantized with a
`stepsize of 8. Each of the other 31 quantizers use equally spaced reconstruction levels with a central dead-zone around
`zero and with a stepsize of an even value in the range 2 to 62. For the exact formulas, refer to 6.2.
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`NOTE – For the smaller quantization stepsizes, the full dynamic range of the transform coefficients cannot be represented.
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`4.3
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`Coding control
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`Several parameters may be varied to control the rate of generation of coded video data. These include processing prior to
`the source coder, the quantizer, block significance criterion and temporal subsampling. The proportions of such
`measures in the overall control strategy are not subject to recommendation.
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`When invoked, temporal subsampling is performed by discarding complete pictures.
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`A decoder can signal its preference for a certain tradeoff between spatial and temporal resolution of the video signal. The
`encoder shall signal its default tradeoff at the beginning of the call and shall indicate whether it is capable to respond to
`decoder requests to change this tradeoff. The transmission method for these signals is by external means (for example,
`Recommendation H.245).
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`4.4
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`Forced updating
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`This function is achieved by forcing the use of the INTRA mode of the coding algorithm. The update pattern is not
`defined. To control the accumulation of inverse transform mismatch error, each macroblock shall be coded in INTRA
`mode at least once every 132 times when coefficients are transmitted for this macroblock in P-pictures.
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`4.5
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`Byte alignment of start codes
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`Byte alignment of start codes is achieved by inserting a stuffing codeword consisting of less than 8 zero-bits before the
`start code such that the first bit of the start code is the first (most significant) bit of a byte. A start code is therefore byte
`aligned if the position of its most significant bit is a multiple of 8-bits from the first bit in the H.263 bit stream. All
`picture start codes shall and GOB and EOS start codes may be byte aligned.
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`NOTES
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`1
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`The number of bits spent for a certain picture is variable but always a multiple of 8 bits.
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`H.324 requires H.263 encoders to align picture start codes with