Context based adaptive coding and the emerging h 26l video compression standard
This presentation is the property of its rightful owner.
Sponsored Links
1 / 27

Context-based Adaptive Coding and the Emerging H.26L Video Compression Standard PowerPoint PPT Presentation


  • 92 Views
  • Uploaded on
  • Presentation posted in: General

Context-based Adaptive Coding and the Emerging H.26L Video Compression Standard. Thomas Wiegand Heinrich Hertz Institute Berlin, Germany [email protected] ITU-T Project H.26L.

Download Presentation

Context-based Adaptive Coding and the Emerging H.26L Video Compression Standard

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Context based adaptive coding and the emerging h 26l video compression standard

Context-based Adaptive Codingand the Emerging H.26L Video Compression Standard

Thomas Wiegand

Heinrich Hertz Institute

Berlin, Germany

[email protected]


Context based adaptive coding and the emerging h 26l video compression standard

ITU-T Project H.26L

  • New ITU-T Q.6/SG16 (VCEG) standardization activity for video coding especially aimed at 3G mobile networks (e.g. UMTS) and broadcast

  • Possible formation of a joint video team with MPEG

  • Goal for H.26L: 50% bit-rate reduction for same fidelity against every existing standard

  • 1999:3 proposalsfor definition of a first test model

    • HHI:Warping/OBMC motion model, wavelet- and context-based adaptive coding (CABAC)

    • Nokia:Affine motion model, multiple block transforms

    • Telenor:Block-matching with variable block-sizes, 4x4-DCT

  • Current Status:Definition of 8th test model (TML-8) based on Telenor proposal

  • Schedule:Final approval in November 2002


Context based adaptive coding and the emerging h 26l video compression standard

Coder

Control

Control

Data

Transform/Quantizer

Quant.Transf. coeffs

-

Decoder

Deq./Inv. Transform

Entropy

Coding

0

Motion-

Compensated

Predictor

Intra/Inter

Motion

Data

Motion

Estimator

H.26L Structure


The h 26l tml 8 design part 1 of 4

Still using a hybrid of DPCM and transform codingas in prior standards.

Common elements with other standards include:

16x16 macroblocks

Conventional sampling of chrominance and association of luminance and chrominance data

Block motion displacement

Motion vectors over picture boundaries

Variable block-size motion

Block transforms (not wavelets or fractals)

Scalar quantization

The H.26L TML-8 Design, Part 1 of 4


Context based adaptive coding and the emerging h 26l video compression standard

Coder

Control

Control

Data

Transform/Quantizer

Quant.Transf. coeffs

-

Decoder

Deq./Inv. Transform

Mode 1

Mode 2

Mode 3

Mode 4

Entropy

Coding

0

0

1

0

0

1

1

2

3

0

Motion-

Compensated

Predictor

Mode 5

Mode 6

Mode 7

0

1

2

3

0

1

0

1

2

3

2

3

4

5

6

7

Intra/Inter

4

5

6

7

4

5

8

9

10

11

6

7

12

13

14

15

Motion

Data

1/4 (QCIF) or 1/8 (CIF) pel

Motion

Estimator

H.26L: Motion Compensation Accuracy


Context based adaptive coding and the emerging h 26l video compression standard

Entropy

Coding

Multiple Reference Frames for

Motion Compensation

H.26L: Multiple Reference Frames

Coder

Control

Control

Data

Transform/Quantizer

Quant.Transf. coeffs

-

Decoder

Deq./Inv. Transform

0

Motion-

Compensated

Predictor

Intra/Inter

Motion

Data

Motion

Estimator


The h 26l tml 8 design part 2 of 4

Motion Compensation:

Various block sizes and shapes for motion compensation (7 segmentations of the macroblock: 16x16, 16x8, 8x16, 8x8, 8x4, 4x8, 4x4)

Multiple reference pictures (per H.263++ Annex U)

Temporally-reversed motion

B picture prediction weighting

New “SP” transition pictures for sequence switching

1/4 sample (sort of per MPEG-4) and 1/8 sample accuracy motion

6x6 tap filtering to 1/2 sample accuracy, bilinear filtering to 1/4 sample accuracy, special position with heavier filtering

8x8 tap filtering applied repeatedly for 1/8 pel motion

The H.26L TML-8 Design, Part 2 of 4


Context based adaptive coding and the emerging h 26l video compression standard

Coder

Control

Control

Data

Transform/Quantizer

Quant.Transf. coeffs

-

Decoder

Deq./Inv. Transform

Entropy

Coding

0

Motion-

Compensated

Predictor

Intra/Inter

Motion

Data

Motion

Estimator

H.26L: Residual Coding

  • Residual coding is based on 4x4 blocks

  • Integer Transform


The h 26l tml 8 design part 3 of 4

Transform

Integer transform approximating a DCT

Based primarily on 4x4 transform size (all prior standards used 8x8)

Expanded to 8x8 for chroma by 2x2 DC transform

Intra Coding Structure

Directional spatial prediction (6 types luma, 1 chroma)

Expanded to 16x16 for luma intra by 4x4 DC Xfm

The H.26L TML-8 Design, Part 3 of 4


The h 26l tml 8 design part 4 of 4

Quantization

Two inverse scan patterns

Logarithmic step size control

Smaller step size for chroma (per H.263 Annex T)

Deblocking Filter (in loop)

Distinct Network Adaptation Layer (NAL) design for network transport

Slice-structure coding

Data partitioning

The H.26L TML-8 Design, Part 4 of 4


Context based adaptive coding and the emerging h 26l video compression standard

Coder

Control

Control

Data

Transform/Quantizer

Quant.Transf. coeffs

-

Decoder

Deq./Inv. Transform

Entropy

Coding

0

Motion-

Compensated

Predictor

Intra/Inter

Motion

Data

Motion

Estimator

H.26L: Entropy Coding


Context based adaptive coding and the emerging h 26l video compression standard

Entropy Coding in H.26L: Type 1 of 2

  • Universal Variable Length Code (UVLC)

    Simple design with some disadvantages:

  • Probability distribution is static

  • Correlations between symbols are ignored, i.e. no conditional probabilities are used

  • Codewords must have integer number of bits(Low coding efficiency for highly peaked pdfs)


Context based adaptive coding and the emerging h 26l video compression standard

Entropy Coding in H.26L: Type 2 of 2

Context-based adaptive binary arithmetic codes(CABAC)

  • Usage of adaptive probability models

  • Exploiting symbol correlations by using contexts

  • Non-integernumber of bits per symbol by using arithmetic codes

  • Restriction to binary arithmetic coding

    • Simple and fast adaptation mechanism

    • But: Binarization is needed for non-binary symbols

    • Binarization enables partitioning of state space


Context based adaptive coding and the emerging h 26l video compression standard

CABAC: Technical Overview

update probability estimation

Context modeling

Probability estimation

Coding engine

Binarization

Adaptive binary arithmetic coder

Uses the provided model for the actual encodingand updates the model

Maps non-binary symbols to a binary sequence

Chooses a model conditioned on past observations


Context based adaptive coding and the emerging h 26l video compression standard

Symbol

Binarization

0

1

1

0 1

2

0 0 1

3

0 0 0 1

4

0 0 0 0 1

5

0 0 0 0 0 1

6

0 0 0 0 0 0 1

.

...

Bin_no

1 2 3 4 5 6 7 ...

Binarization

  • Mapping to a binary sequence using the unary code tree:

  • Applies to all non-binary syntax elements except for macroblock type

  • Ease of implementation

  • Optimal codes for a geometric pdfp(x) = 2–(x+1)

  • Discriminate between binary decisions (bins) by their position in the binary sequence

  •  Usage of different models for different bin_numbers in the arithmetic coder


Context based adaptive coding and the emerging h 26l video compression standard

0, for A+B < 2,

1, else

ctx_no (C) =

B

A

C

Example: Context Modeling and Binarization

Neighboring symbols A and B used for conditioning of current symbol C

Context determination rule

Current symbol

C=4

A=2, B=3  ctx_no(C)=1

Context selection

0 0 0 0 1

Binarization

Choice of model depends on bin_no

(bit, model_no.): (0,1) (0,2) (0,3) (0,3) (1,3)

Feed into the arithmetic coder


Context based adaptive coding and the emerging h 26l video compression standard

Probability Estimation and Adaptation

  • Each model only consists of two counters: counts(„0“), counts(„1“)

  • Coding with multiple contexts (models) is easy to obtain because of a clean interface between model and coder

  • Model (probability estimate) is updated after each symbol is encoded  adaptive model


Context based adaptive coding and the emerging h 26l video compression standard

Binary Arithmetic Coding

  • Standard implementations use integer arithmetic

  • Fast,multiplication-free variants of binary arithmetic coder exists: e.g. MQ-coder used in JBIG-2, JPEG-LS, JPEG-2000

  • Estimation: Increasein computational complexity lower than 10% (MQ) and 20% (Standard-AC) of the total decoder execution time at medium bitrate


Context based adaptive coding and the emerging h 26l video compression standard

Results: Bit-Rate Reduction


Context based adaptive coding and the emerging h 26l video compression standard

Results: Bit-Rate Reduction


Comparison of h 26l to mpeg 4

MPEG-4: Advanced Simple Profile (ASP)

Motion Compensation: 1/4 pel

Global Motion Compensation

H.26L:

Motion Compensation: 1/4 pel (QCIF), 1/8 pel (CIF)

Using CABAC entropy coding

5 reference frames in 7 of 8 cases (News: 17 / 25)

Both:

Sequence structure IBBPBBP...

QPB=QPP+2 (step size: +25%)

Search range: 32x32 around 16x16 predictor

Well-known D+lR optimization techniques

Comparison of H.26L to MPEG-4


Context based adaptive coding and the emerging h 26l video compression standard

RD Curves: Foreman (QCIF, 10Hz)

39

38

37

36

35

34

33

Average PSNR(Y) [dB]

32

31

30

29

28

MPEG-4

27

H.26L

26

0

16

32

48

64

80

96

112

128

Bit-rate [kbit/s]


Context based adaptive coding and the emerging h 26l video compression standard

RD Curves: Flowergarden (CIF, 30Hz)

38

37

36

35

34

33

32

31

Average PSNR(Y) [dB]

30

29

28

27

26

25

MPEG-4

24

23

H.26L

22

0

256

512

768

1024

1280

1536

1792

2048

2304

Bit-rate [kbit/s]


Psnr results h 26l tml8 vs mpeg 4 asp anchor

PSNR Results: H.26L TML8vs. MPEG-4 ASP Anchor


Context based adaptive coding and the emerging h 26l video compression standard

PSNR Results: H.26L TML8vs. MPEG-4 ASP Anchor


Context based adaptive coding and the emerging h 26l video compression standard

Subjective Comparison


Context based adaptive coding and the emerging h 26l video compression standard

Conclusions

  • Draft H.26L design is based on hybrid video coding

  • Similar in spirit to other standards but with important differences

  • Entropy coding can be conducted using

    • One VLC

    • Context-based adaptive arithmetic coding

  • Context-based adaptive arithmetic coding provides improvements between 5-15 %

  • H.26L shows a significant performance gain over existing standards including MPEG-4

  • Bit-rate savings up to 50 % against MPEG-4 ASP


  • Login