1. Overview of H.264/AVC x
M.K.Tsai

2. Outline Abstract Applications Network Abstraction Layer,NAL
Conclusion—(I)
Design feature highlight
Conclusion—(II)
Video Coding Layer,VCL
Profile and potential application
Conclusion—(III)

3. abstract H.264/AVC is newest video coding standard
Main goals have been enhanced compression and provision of “network-friendly” representation addressing “conversational”(video telephony) and “nonconversational” (storage,broadcast, or streaming) application
H.264/AVC have achieved a significant improvement in rate-distortion efficiency
Scope of standardization is illustrated below

4. applications Broadcast over cable, cable modem …
Interactive or serial storage on optical and DVD …
Conversational service over LAN, modem …
Video-on-demand or streaming service over ISDN,wireless network …
Multimedia message service (MMS) over DSL, mobile network …
How to handle the variety of applications and networks ?

5. applications
To address this need for flexibility and customizability, the H.264/AVC design VCL and NAL, structure of H.264/AVC encoder is shown below

6. applications
VCL(video coding layer), designed to efficiently represent video content
NAL(network abstraction layer), formats the VCL representation of the video and provides header information in a manner appropriate for conveyance by a variety of transport layers or storage media

7. Network Abstraction Layer
To provide “network friendliness” to enable simple and effective customization of the use of the VCL
To facilitate the ability to map H.264/AVC data to transport layers such as :
RTP/IP for kind of real-time Internet services
File formats,ISO MP4 for storage
H.32X for conversational services
MPEG-2 systems for broadcasting services
The design of the NAL anticipates a variety of such mappings

8. Network Abstraction Layer
Some key concepts of the NAL are NAL units, byte stream, and packet format uses of NAL units, parameter sets and access units …
NAL units
a packet that contains an integer number of bytes
First byte is header byte containing indication of type of data
Remaining byte contains payload data
Payload data is interleaved as necessary with emulation prevention bytes, preventing start code prefix from being generated inside payload
Specifies a format for use in both packet- and bitstream- oriented transport system

9. Network Abstraction Layer
NAL units in Byte-Stream format use
byte stream format
Each is prefixed by a unique start code to identify the boundary
Some systems require delivery of NAL unit stream as ordered stream of bytes (like H.320 and MPEG-2/H.220)
NAL units in packet-transport system use
Coded data is carried in packets framed by system transport protocol
Can be carried by data packets without start code prefix
In such system, inclusion of start code prefixes in data would be waste

10. Network Abstraction Layer
VCL and Non-VCL NAL units
VCL NAL units contain data represents the values of the samples in video pictures
Non- VCL NAL units contain extra data like parameter sets and supplemental enhancement information (SEI)
parameter sets, important header data applying to large number of VCL NAL units
SEI, timing information and other supplemental data enhancing usability of decoded video signal but not necessary for decoding the values in the picture

11. Network Abstraction Layer
Parameter sets
Contain information expected to rarely change and offers the decoding of a large number of VCL NAL units
Divided into two types
Sequence parameter sets, apply to series of consecutive coded video picture
Picture parameter sets, apply to the decoding of one or more individual picture within a coded video sequence
The above two mechanisms decouple transmission of infrequently changing information
Can be sent well ahead of the VCL NAL units and repeated to provide robustness against data loss

12. Network Abstraction Layer
Parameter sets
Can be sent well ahead of the VCL NAL units and repeated to provide robustness against data loss
Small amount of data can be used (identifier) to refer to a larger amount of of information (parameter set)
In some applications, these may be sent within the channel (termed “in-band” transmission)

13. Network Abstraction Layer
Parameter sets
In other applications, it can be advantageous to convey parameters sets “out of band” using reliable transport mechanism

14. Network Abstraction Layer
Access units
The format of access unit is shown below

15. Network Abstraction Layer
Access units
Contains a set of VCL NAL units to compose a primary coded picture
Prefixed with an access unit delimiter to aid in locating the start of the access unit
SEI contains data such as picture timing information
Primary coded data consists of VCL NAL units consisting of slices that represent the sample of the video
Redundant coded picture are available for use by decoder in recovering from loss of data

16. Network Abstraction Layer
Access units
For the last coded picture of video sequence, end of sequence NAL unit is present to indicate the end of sequence
For the last coded picture in the entire NAL unit stream, end of stream NAL unit is present to indicate the stream is ending
Decoder are not required to decode redundant coded pictures if they are present
Decoding of each access unit results in one decoded picture

17. Network Abstraction Layer
Coded video sequences
Consists of a series of access unit and use only one sequence parameter set
Can be decoded independently of other coded video sequence ,given necessary parameter set
Instantaneous decoding refresh(IDR) access unit is at the beginning and contains intra picture
Presence of IDR access unit indicates that no subsequent picture will reference to picture prior to intra picture

18. Conclusion—(I)
H.264/AVC represents a number of advances in standard video coding technology in term of flexibility for effective use over a broad variety of network types and application domain

19. Design feature highlight
Variable block-size motion compensation with small block size
With minimum luma block size as small as 4x4
The matching chroma is half the length and width

20. Design feature highlight
Quarter-sample-accurate motion compensation
Half-pixel is generated by using 6 tap FIR filter
As first found in advanced profile of MPEG-4, but further reduces the complexity
Multiple reference picture motion compensation
Extends upon enhanced technique found in H.263++
Select among large numbers of pictures decoded and stored in the decoder for pre-prediction
Same for bi-prediction which is restricted in MPEG-2

21. Design feature highlight
Decoupling of reference order from display order
A strict dependency between ordering for referencing and display in prior standard
Allow encoder to choose ordering of pictures for referencing and display purposes with a high degree of flexibility
Flexibility is constrained by total memory capability
Removal of restriction enable removing extra delay associated with bi-predictive coding

22. Design feature highlight
Motion vector over boundaries
Motion vectors are allowed to point outside pictures
Especially useful for small picture and camera movement
Decoupling of picture representation methods from picture referencing capability
Bi-predictively-encoded pictures could not be used as references in prior standard
Provide the encoder more flexibility to use a picture for referencing that is closer to the picture being coded

23. Design feature highlight
Weighted prediction
Allow motion-compensated prediction signal to be weighted and offset by amounts
Improve coding efficiency for scenes containing fades
one grid means one pixel

24. Design feature highlight
Improved skipped and direct motion inference
In prior standard ,”skipped” area of a predictively-coded picture can’t motion in the scene content ,which is detrimental for global motion
Infers motion in “ skipped ” motion
For bi-predictively coded areas ,improves further on prior direct prediction such as H.263+ and MPEG-4.

25. Design feature highlight
Directional spatial prediction for intra coding
Extrapolating edges of previously decoded parts of current picture is applied in intra-coded regions of picture
Improve the quality of the prediction signal
Allow prediction from neighboring areas that were not intra-coded

26. Design feature highlight
In-the-loop deblocking filtering
Block-based video coding produce artifacts known as blocking artifacts originated from both prediction and residual difference coding stages of decoding process
Improvement in quality can be used in inter-picture prediction to improve the ability to predict other picture

27. Design feature highlight
In addition to improved prediction methods coding efficiency is also enhanced, including the following
Small block-size transform
All major prior video coding standards used a transform block size of 8x8 while new ones is based primarily on 4x4
Allow the encoder to represent the signal in a more locally-adaptive fashion and reduce artifact
Short word-length transform
Arithmetic processing 32-bit  16-bits

28. Design feature highlight
Hierarchical block transform
Extend the effective block size for low-frequency chroma to 8x8 array and luma to 16x16 array

29. Design feature highlight
Exact-match inverse transform
Previously transform was specified within error tolerance bound due to impracticality of obtaining exact match to ideal inverse transform
Each decoder would produce slightly different decoded video, causing “drift” between encoder and decoder
Arithmetic entropy coding
Previously found as an optional feature of H.263
Use a powerful “Context-adaptive binary arithmetic coding”(CABAC)

30. Design feature highlight
Context-adaptive entropy coding
Both “CAVLC (context-adaptive variable length coding)” and “CABAC” use context-based adaptivity to improve performance

31. Design feature highlight
Robustness to data errors/losses and flexibility for operation over variety of network environments is enable, including the following
Parameter set structure
Key information was separated for handling in a more flexible and specialize manner
Provide for robust and efficient conveyance header information
Flexible slice size
Rigid slice structure reduce coding efficiency by increasing the quantity of header data and decreasing the effectiveness of prediction in MPEG-2

32. Design feature highlight
NAL unit syntax structure
Each syntax structure in H.264/AVC is placed into a logical data packet called a NAL unit
Allow greater customization of the method of carrying the video content in a manner for each specific network
Redundant pictures
Enhance robustness to data loss
Enable a representation of regions of pictures for which the primary representation has been lost

33. Design feature highlight
Flexible macroblock ordering (FMO)
Partition picture into regions called slice groups, with each slice becoming independently decodable subset of a slice group
Significantly enhance robustness by managing the spatial relationship between the regions that are coded in each slice
Arbitrary slice ordering (ASO)
Enable sending and receiving the slices of the picture in any order relative to each other as found in H.263+
Improve end-to-end delay in real time applications particularly for out-of-order delivery behavior

34. Design feature highlight
Data partitioning
Allow the syntax of each slice to be separated into up to three different partitions(header data, Intra-slice, Inter-slice, partition), depending on a categorization of syntax elements
SP/SI synchronization/switching pictures
Allow exact synchronization of the decoding process of some decoder with an ongoing video
Enable switching a decoder between video streams that use different data rate, recover from data loss or error
Enable switching between different kind of video streams, recover from data loss or error

35. Design feature highlight
SP/SI synchronization/switching pictures

36. Design feature highlight
SP/SI synchronization/switching pictures

37. Conclusion—(II)
H.264/AVC represents a number of advances in standard video coding technology in term of both coding efficiency enhancement and flexibility for effective use over a board variety of network types and application domain

38. Video Coding Layer Pictures, Frames, and Fields
Picture can represent either an entire frame or a single field
If two fields of a frame were captured at different time instants the frame is referred to as a interlaced frame, otherwise it is referred to as a progressive frame

39. Video Coding Layer YCbCr color space and 4:2:0 sampling
Y represents brightness
Cb、Cr represents color deviates from gray toward blue and red
Division of the picture into macroblock
Slices and slice groups
Slices are a sequence of macroblocks processed in the order of a raster scan when not using FMO
Some information from other slices maybe needed to apply the deblocking filter across slice boundaries

40. Video Coding Layer
Picture may be split into one or more slices without FMO shown below
FMO modifies the way how pictures are partitioned into slices and MBs by using slice groups
Slice group is a set of MBs defined by MB to slice group map specified by picture parameter set and some information from slice header

41. Video Coding Layer
Slice group can be partitioned into one or more slices, such that a slice is a sequence of MBs within same slice group processed in the order of raster scan
By using FMO, a picture can be split into many macroblock scanning patterns such as the below

42. Video Coding Layer Each slice can be coding using different types
I slice
A slice where all MBs are coded using intra prediction
P slice
In addition to intra prediction, it can be coded with inter prediction with at most one motion-compensated prediction
B slice
In addition to coding type of P slice, it can be coded with inter prediction with two motion-compensated prediction
SP (switching P) slice
Efficient switching between different pre-coded pictures
SI (switching I) slice
Allows exact match of a macroblock in an SP slice for random access and error recovery

43. Video Coding Layer
If all slices in stream B are P-slices, decoder won’t have correct reference frame, solution is to code frame as an I-slice like below
I-slice result in a peak in the coded bit rate at each switching point

44. Video Coding Layer
SP-slices are designed to support switching without increased bit-rate penalty of I-slices
Unlike “ normal ” P-slice, the subtraction occurs in transform domain

45. Video Coding Layer
A simplified diagram of encoding and decoding processing for SP-slices A2、B2、AB2 is shown (A’ means reconstructed frame)

46. Video Coding Layer
If stream A and B are versions of the same original sequence coded at different bit-rates the SP-slice AB2 should be efficient

47. Video Coding Layer
SP-slices is to provide random access and “VCR-like” functionalities.(e.g decoder can fast-forward from A0 directly to frame A10 by first decoding A0, then decoding SP-slice A0-10)
Second type of switching slice, SI-slice may be used to switch from one sequence to a completely different sequence

48. Video Coding Layer Encoding and decoding process for macroblocks
All luma and chroma samples of a MB are either spatially or temporally predicted
Each color component of prediction is subdivided into 4x4 blocks and is transformed using integer transform and then be quantized and encoded by entropy coding methods
The input video signal is split into MBs, the association of MBs to slice groups and slices is selected
An efficient parallel processing of MB is possible when there are various slices in the picture

49. Video Coding Layer Encoding and decoding process for macroblocks
block diagram of VCL for a MB is in the following

50. Video Coding Layer Adaptive frame/field coding operation
For regions of moving objects or camera motion, two adjacent rows show a reduced degree of dependency in interlaced frames but progressive frames
To provide high coding efficiency, H.264/AVC allows the following decisions when coding a frame
To combine two fields and code them as one single frame (frame mode)
To not combine the two fields and to code them as separated coded fields (field mode)
To combine the two fields and compress them as a single frame, before coding them to split the pairs of the vertically adjacent MB into pairs of two fields or frame MB

51. Video Coding Layer
The three options can be made adaptively and the first two can be is referred to as picture-adaptive frame/field (PAFF) coding
As a frame is coded as two fields, coded in ways similar to frame except the following
Motion compensation utilizes reference fields rather frames
The zig-zag scan is different
Strong deblocking is not used for filtering horizontal edges of MB in fields
A frame consists of mixed regions, it’s efficient to code the nonmoving regions in frame mode, moving regions in field mode

52. Video Coding Layer
A frame/field encoding decision can be made independently for each vertical pairs of MB. The coding option is referred as macroblock-adaptive frame/field (MBAFF) coding. The below shows the MBFAA MB pair concept.

53. Video Coding Layer
An important distinction between PAFF and MBAFF is that in MBAFF, one field can’t use MBs in other field of the same frame
Sometimes PAFF coding can be more efficient than MBAFF coding, particularly in the case of rapid global motion, scene change, intra picture refresh

54. Video Coding Layer Intra frame prediction
In all slice coding type Intra_4x4 or intra_16x16 together with chroma prediction and I_PCM prediction mode
Intra_4x4 mode is based on 4x4 luma block and suited for significant detail of picture
When using, each 4x4 block is predicted from the neighboring samples like the below

55. Video Coding Layer Intra frame prediction 4x4 block prediction mode
Suited to predict textures with structure in the specified direction except the “DC” mode prediction

56. Video Coding Layer Intra frame prediction
In earlier draft, the four samples below L were also used for some prediction modes. They are dropped due to the need to reduce memory access
Intra modes for neighboring 4x4 block are highly correlated. For example, if previously-encoded 4x4 blocks A and B were predicted mode 2, it’s likely that the best mode for block C is also mode 2.

57. Video Coding Layer Intra frame prediction
Intra_16x16 mode is suited for smooth areas of a picture
When using this mode, it contains vertical、horizontal、DC and plane prediction
Plane prediction works well in areas of smoothly-varying luminance

58. Video Coding Layer Intra frame prediction
Chroma of MB is predicted by the similar prediction as Intra_16x16(the same four modes)
I_PCM mode allows the encoder to bypass the prediction and transform coding process and instead directly send the values of the encoded samples
I_PCM mode server the following purposes
Allow the encoder to precisely represent the value of samples
Provide a way to accurately represent the values of anomalous picture content
Enable placing a hard limit on the number of bits, decoder must handle for MB without harm to coding efficiency

59. Video Coding Layer Intra frame prediction
Constrained intra coding mode allows prediction only from intra-coded neighboring MBs
Intra prediction across slice boundaries is not used
Referring to neighboring samples of previously-coded blocks may incur error propagation in environments with transmission error

60. Video Coding Layer Inter frame prediction In P slices
Each P MB type is partitioned into partitions like the below
This method of partitioning MB is known as tree structure motion compensation

61. Video Coding Layer Inter frame prediction
Choosing larger partition size means
Small number of bits are required to signal the choice of MV and the type of partition
Motion compensated residual contain a significant amount of energy in frame areas with high detail
Choosing small partition size means
Give a lower-energy residual after motion compensation
Require larger number of bits to signal MV and type of partition
The accuracy of motion compensation is in units of one quarter of the distance between two luma sample

62. Video Coding Layer Inter frame prediction
Half-sample values are obtained by applying a one-dimensional 6-tap FIR filter vertically and horizontally
6 tap interpolation filter is relatively complex but produces more accurate fit to the integer-sample data and hence better motion compensation performance
Quarter-sample values are generated by averaging samples at integer- and half-sample position

63. Video Coding Layer

64. Video Coding Layer
The above illustrates the half sample interpolation

65. Video Coding Layer Inter frame prediction a = round ((G+b)/2)
The following illustrates the luma quarter-pel positions
a = round ((G+b)/2)
d = round ((G+h)/2)
e = round ((h+b)/2)

66. Video Coding Layer
The prediction for chroma component are obtained by bilinear interpolation
The displacements used for chroma have one-eighth sample position accuracy
a = round([(8-dx)(8-dy)A + dx(8-dy)B + (8-dx)dyC + dxdyD]/64)

67. Video Coding Layer Inter frame prediction
Motion prediction using full,half,and one-quarter sample have improvements than the previous standards for two reasons
More accurate motion representation
More flexibility in prediction filtering
Allows MV over picture boundaries
No MV prediction takes place across slice boundaries
Motion compensation for smaller regions than 8x8 use the same reference index for prediction of all blocks within 8x8

68. Video Coding Layer Inter frame prediction
Choice of neighboring partitions of same and different size are shown below
For transmitted partitions, excluding 16x8 and 8x16 partition sizes: MVp is the median of the MV for partitions A,B,C

69. Video Coding Layer
For 16x8 partitions: MVp for the upper 16x8 partition is predicted from B, MVp for the lower 16x8 partition is predicted from A
For 8x16 partitions: MVp for the left 8x16 partition is predicted from A, MVp for the right 8x16 partition is predicted from C
For skipped macroblocks: a 16x16 vector MVp is generated as in case(1) above

70. Video Coding Layer
P MB can be coded in P_Skip type useful for large areas with no change or constant motion like slow panning can be represented with very few bits
Support multi-picture motion-compensation like below

71. Video Coding Layer In B slices Intra coding are also supported
Four other types are supported : list 0, list 1, bi-predictive, and direct prediction
For bi-predictive mode, the prediction signal is formed by a weighted average of motion-compensation list 0 and list 1 prediction signal
The direct mode can be list 0 or list 1 prediction or bi-predictive
Support multi-frame motion compensation

72. Video Coding Layer Transform, scaling, quantization
Transform is applied to 4x4 block
Instead of DCT, a separated integer transform with similar properties as DCT is used
Inverse transform mismatches are avoided
At encoder, transform, scanning, scaling, and rounding as quantization followed by entropy coding
At decoder, process of inverse encoding is performed except for the rounding
Inverse transform is implemented using only additions and bit-shifting operations of 16 bit

73. Video Coding Layer Several reasons for using smaller size transform
Remove statistical correlation efficiently
Have visual benefits resulting in less noise around edges
Require less computations amd a smaller processing word-length
Quantization parameter(QP) can take 52 values
Qstep double in size for every increment of 6 in QP
With increasing 1 of QP means increasing 12.5% Qstep

74. Video Coding Layer
Wide range of quantizer step size make it possible for encoder to control the trade-off between bit rate and quality accurately and flexibly
The values of QP may be different from luma and chroma. QPchroma is derived from QPY by user-defined offset
4x4 luma DC coefficient and quantization (16x16 intra mode only )
The DC coefficient of each 4x4 block is transformed again using 4x4 Hadamard transform
In a intra-coded MB, much energy is concentrated in the DC coefficients and this extra transform helps to de-correlate the 4x4 luma DC coefficients

75. Video Coding Layer
2x2 chroma DC coefficient transform and quantization, as with Intra luma DC coefficients, the extra transform help to de-correlate the 2x2 chroma DC coefficients and improve compression performance
The complete process
Encoding：
Input： 4x4 residual samples：
Forward “core” transform：
( followed by forward transform for Chroma DC or Intra-16 Luma DC coefficients)
Post-scaling and quantization：
( modified for Chroma DC or Intra-16 Luma DC)

76. Video Coding Layer Decoding ：
( inverse transform for chroma DC or intra-16 luma DC coefficient )
Re-scaling ( incorporating inverse transform pre-scaling )：
(modified for chroma DC or Intra-16 Luma DC coefficients)
Inverse “core” transform：
Post-scaling：
Output：4x4 residual samples：

77. Video Coding Layer Flow chart
An additional 2x2 transform is also applied to DC coefficients of the four 4x4 blocks of chroma

78. Video Coding Layer Entropy coding
Simpler method use a single infinite-extent codeword table for all syntax elements except residual
mapping of codeword table is customized according to data statistics
Codeword table chosen is an exp-Golomb code with simple and regular decoding property
In CAVLC, VLC tables for various syntax elements are switched depending on already transmitted syntax elements
In CAVLC, number of non-zero quantized coefficient and actual size and position of the coefficients are coded separately

79. Video Coding Layer Entropy coding
VLC tables are designed to match the corresponding conditioned statistics
CAVLC encoding of a block of transform coefficients proceeds as follows
Encode number of non-zero coefficients and “ trailing 1s ”
Encode total number of non-zero coefficients(TotalCoeffs) and trailing +/-1 values(T1)  coeff_token
TotalCoeffs:0~16 ,T1:0~3
There are 4 look-up tables for coeff_token (3 VLC and 1 FLC)
Encode the sign of each T1
Coded in reverse order, starting with highest-frequency

80. Video Coding Layer Entropy coding
Encoding levels of remaining non-zero coefficients
Coded in reverse order
There are 7 VLC tables to choose from
Choice of table adapts depending on magnitude of coded level
Encode total number of zeros before last coefficient
TotalZeros is sum of all zeros preceding the highest non-zero coefficient in the reorder array
Coded with a VLC
Encode each run of zeros
Encoded in reverse order
Chosen depending on ZerosLeft、run_before

81. Video Coding Layer
Entropy coding
example

82. Video Coding Layer
Entropy coding
example

83. Video Coding Layer
Entropy coding
example

84. Video Coding Layer
In CABAC, it allows assignment of a non-integer number of bits to each symbol of an alphabet
Usage of adaptive codes permits adaptation to non-stationary symbol statistics
Statistics of already coded syntax elements are used to estimate conditional probabilities used for switching several estimated models
Arithmetic coding core engine and its associated probability estimation are specified as multiplication-free low complexity methods using only shift and table look-ups

85. Video Coding Layer
Coding a data symbol involves the following stages (take MVDx)
Binarization
For |MVDX|<9 it’s carried out by following table, larger values are by Exp-Golomb codeword
the first bit is bin 1,second bit is bin 2

86. Video Coding Layer
Coding a data symbol involves the following stages (take MVDx)
Context model selection
It’s by following table
Arithmetic encoding
Selected context model supplies two probability estimates (1 and 0) to determine sub-range the arithmetic coder uses

87. Video Coding Layer
Coding a data symbol involves the following stages (take MVDx)
Probability update
The value of bin 1 is “0”, the frequency count of “0” is incremented

88. Video Coding Layer In-loop deblocking filter
Applied between inverse transform and reconstruction of MB
Particular characteristics of block-based coding is the accidental production of visible block structures
Block edges are reconstructed with less accuracy than interior pixels and “blocking” is most visible artifacts
It has two benefits
Block edges are smoothed
Resulting in a smaller residuals after prediction
In adaptive filter, strength of filtering is controlled by several syntax elements

89. Video Coding Layer In-loop deblocking filter
Basic idea is that if a relatively larger absolute difference between samples near a block edge is measured , it is quite likely a blocking artifact and should be reduced
If magnitude of difference is large and can’t be explained by coarse quantization, it’s likely actual behavior of picture
Filtering is applied 4x4 block

90. Video Coding Layer In-loop deblocking filter
Filtering is applied 4x4 block
Choice of filtering outcome depends on boundary strength and gradient of image across boundary

91. Video Coding Layer In-loop de-blocking filter
Boundary strength Bs is chosen according to following table
Filter implementation
Bs {1,2,3}：a 4-tap linear filter is applied
Bs {4}： 3、4、5-tap linear filter may be used

92. Video Coding Layer Below shows principle using one dimensional edge
Samples p0 and q0 as well as p1 and q1 are filtered is determined using quantization parameter (QP) dependent thresholds α(QP) and β(QP), β(QP) is smaller than α(QP)

93. Video Coding Layer
Filtering of p0 and q0 takes place if each of the below is satisfied
1. |p0 – q0| < α(QP)
2. |p1 – p0| < β(QP)
3. |q1 – q0| < β(QP)
Filtering of p1 and q1 takes place if the below is satisfied
1. |p2 – p0| < β(QP)
or |q2 – q0| < β(QP)

94. Video Coding Layer
Foreman.cif 30 Hz
Foreman.qcif 10 Hz

95. Video Coding Layer Hypothetical reference decoder (HRD)
For a standard, it’s not sufficient to provide a coding algorithm
It’s important in real-time system to specify how bits are fed to a decoder and how the decoded pictures are removed from decoder
Specifying input and output buffer models and developing an implementation independent model of receiver called HRD
Specifies operation of two buffers
Coded picture buffer (CPB)
Decoded picture buffer (DPB)

96. Video Coding Layer
CPB models arrival and removal time of the coded bits
HRD is more flexible in support of sending video at variety of bit rates without excessive delay
HRD specifies DPB model management to ensure that excessive memory capability is not needed

97. Profile and potential application
Profiles
Three profiles are defined, which are Baseline, Main, and Extended profiles.
Baseline support all features except the following
B slice, weighted prediction, CABAC, field coding, and picture or MB adaptive switching between frame/field coding
SP/SI slices, and slices data partition
Main profile supports first set of above but FMO, ASO, and redundant pictures
Extended profile supports all features of baseline and the above both set except for CABAC

98. Profile and potential application
Areas for profiles of new standard to be used
A list of possible application areas is list below
Conversational services
H.323 conversational video services that utilize circuit–switched ISDN-based video conference
H.323 conversational services over internet with best effort IP/RTP protocols
Entertainment video applications
Broadcast via satellite, cable or DSL
DVD for standard
VOD(video on demand) via various channels

99. Profile and potential application
Streaming services
3GPP streaming using IP/RTP for transport and RSTP for session setup
Streaming over wired Internet using IP/RTP protocol and RTSP for session
Other services
3GPP multimedia messaging services
Video mail

100. Conclusion—(III)
Its VCL design is based on convectional block-based hybrid video coding concepts, but with some differences relative to prior standard, they are illustrated below
Enhanced motion-prediction capability
Use of a small block-size exact-match transform
Adaptive in-loop de-blocking filter
Enhanced entropy coding methods