advanced video compression standards

1. Advanced Video Compression Standards Gary Sullivan (GarySull@microsoft.com) Microsoft Corp. Software Design Engineer ITU-T Rapporteur of Advanced Video Coding ITU-T Recommendation H.263 Editor Stanford, February 15, 2001

3. Formal Standards Specification available to all at little or no cost Anyone allowed to implement Agreement officially by consensus, not decided by a single organization’s interests Relatively open committee with variety of participants (including hostile competitors, with no contract to support a common agenda, often meeting with formal government approval) In practice, each standards organization tends to have its own “personality”

4. Video CodingStandardization Organizations Two organizations dominate video compression standardization: ITU-T Video Coding Experts Group (VCEG) International Telecommunications Union – Telecommunications Standardization Sector (ITU-T, a United Nations Organization, formerly CCITT), Study Group 16, Question 6 ISO/IEC Moving Picture Experts Group (MPEG) International Standardization Organization and International Electrotechnical Commission, Joint Technical Committee Number 1, Subcommittee 29, Working Group 11

5. Dynamics of the VideoStandardization Process VCEG is older and more focused on conventional (esp. low-delay) video coding goals (e.g. good compression and packet-loss/error resilience) MPEG is larger and takes on more ambitious goals (e.g. “object oriented video”, “synthetic-natural hybrid coding”, and digital cinema) Sometimes the major organizations team up (e.g. ISO, IEC and ITU teamed up for both MPEG-2 and JPEG) Relatively little industry consortium activity (DV and organizations that tweak the video coding standards in minor ways, such as DVD, 3GPP, 3GPP2, SMPTE, IETF, etc.) Growing activity for internet streaming media outside of formal standardization (e.g., Microsoft, Real Networks, Quicktime)

6. The Scope of Picture and Video Coding Standardization Only the Syntax and Decoder are standardized: Permits optimization beyond the obvious Permits complexity reduction for implementability Provides no quality guarantees – only interoperability

7. H.261: The Basis of Modern Video Compression ITU-T (ex-CCITT) Rec. H.261: The first widespread practical success First design (late ‘90) embodying typical structure that dominates today: 16x16 macroblock motion compensation, 8x8 DCT, scalar quantization, and variable-length coding Key aspects later dropped by other standards: loop filter, integer motion comp., 2-D VLC, header overhead v2 (early ‘93) added a backward-compatible high-resolution graphics trick mode Operated at 64-2048 kbps Still in use, although mostly as a backward-compatibility feature – overtaken by H.263

8. Typical MC+DCT Video Coder

9. Video Coding Efficiency

10. MPEG-1:Practicality at Higher Bit Rates Formally ISO/IEC 11172-2 (‘93), developed by ISO/IEC JTC1 SC29 WG11 (MPEG) – use is fairly widespread, but mostly overtaken by MPEG-2 Superior quality to H.261 when operated a higher bit rates (? 1 Mbps for CIF 352x288 resolution) Can provide approximately VHS quality between 1-2 Mbps using SIF 352x240/288 resolution Technical features: Adds bi-directional motion prediction and half-pixel motion to H.261 design

11. MPEG-2/H.262: Even Higher Bit Rates and Interlace Formally ISO/IEC 13818-2 & ITU-T H.262, developed (‘94) jointly by ITU-T and ISO/IEC SC29 WG11 (MPEG) – Now in wide use for DVD and standard and high-definition DTV (the most commonly used video coding standard) Primary new technical features: support for interlaced-scan pictures and scalability Essentially the same as MPEG-1 for progressive-scan pictures, and MPEG-1 forward compatibility required Not especially useful below 4 Mbps (range of use normally 5-30 Mbps)

12. H.263: The Next Generation ITU-T Rec. H.263 (v1: 1995): The next generation of video coding performance, developed by ITU-T – the current best standard for practical video telecommunication (has overtaken H.261 as dominant videoconferencing codec) Superior to H.261 at all bit rates Wins by a factor of two at very low rates Versions 2 (late 1997/early 1998) & v3 (2000) later developed

13. MPEG-4: Baseline H.263and Many Creative Extras MPEG-4 (v1: early 1999), formally ISO/IEC 14496-2: Contains the H.263 design and adds all prior features and various creative new extras Includes segmented coding of shapes, zero-tree wavelet coding of still textures, coding of synthetic and semi-synthetic content, etc. v2 (early 2000) & v3 (early 2001) later added

14. MPEG-4 and H.263 Standardization Dynamics MPEG-4 project launched soon after H.263 completed MPEG-4 project was very ambitious and was planned to be significantly different from H.263 Compatibility with H.263 was not initially planned in MPEG-4 (although it eventually turned out to be significantly compatible!) ITU-T decided to extend its H.263 quickly and compatibly rather than join up with longer, more ambitious, potentially-incompatible MPEG-4 effort for the features the ITU wanted Much cross-fertilization of ideas and people in projects

15. Detailed Recent History In Video Coding Standardization ITU-T Events H.263v1 completed late ‘95 H.263+ project (H.263 v2) technically final Sept ‘97 H.263++ project (H.263 v3) technically final July ‘00 H.26L project underway (test version available) ISO/IEC Events MPEG-4 v1 completed early ’99 MPEG-4 v2 completed early ’00 MPEG-4 v3 completed early ‘01 Potential for new work under evaluation

16. H.263++ New Version 3 FeaturesPart 1 of 2 Annex U: Fidelity enhancement by macroblock and block-level reference picture selection – a significant improvement in compression quality Annex V: Packet Loss & Error Resilience using data partitioning with reversible VLCs (roughly similar to MPEG-4 data partitioning, but improved by using reversible coding of motion vectors rather than coefficients)

17. H.263++ New Version 3 FeaturesPart 2 of 2 Annex W:Additional Supplemental Enhancement Information IDCT Mismatch Elimination (specific fixed-point fast IDCT) Arbitrary binary user data Text messages (arbitrary, copyright, caption, video description, and URI) Error Resilience: Picture header repetition (current, previous, next+TR, next-TR) Spare reference pictures for error concealment Interlaced field indications (top & bottom)

20. MPEG-4 Version 3 Just Completed (part 1 of 2) “Studio Profile” Various additions oriented toward professional use of video within specialized studio environments Adds 4:2:2 and 4:4:4 sampling structures Adds more MPEG-2 elements to MPEG-4 “Fine Granularity Scalability Streaming Video Profile”, a new form of scalable video coding Uses a scalable enhancement layer Temporal prediction in enhancement layer is stopped to prevent temporal error propagation Enhancement layer coded by bit-planes to form a “progressive-transmission” bitstream

21. MPEG-4 Version 3Just Completed (part 2 of 2) “Advanced Simple Profile”, a combination of v1 features, containing: “Simple Profile” features B pictures MPEG-2-style quantization Interlace features (at higher levels only) ¼-pel motion Global motion comp Single stream support in new “level 0”

22. ITU-T VCEG H.26L ProjectGoals (Completion 2002) Compression beyond capability of H.263vN Real-time low-cost complexity Delay reduction Enhanced error and packet loss resilience Bit-rate adaptivity (e.g. scalability & BR reduction) Spatio-temporal resolution adaptivity Robustness to source material behavior

23. H.26L Status Test Model Long-Term Number 6: Designed January ’01 (Eibsee), description and software soon available on the ‘net TML-5 software and spec availalbe (Geneva, November ’00) Gain goal over 1999 standards:50% savings in bits for same fidelity!(at all bit rates)

24. The H.26L TML-6 DesignPart 1 of 4 Still using a hybrid of DPCM and transform coding as in prior standards. Common elements include: 16x16 macroblocks Conventional sampling of chrominance and association of luminance and chrominance data Block motion displacement Block transforms (not wavelets or fractals) Scalar quantization Variable-length coding

25. The H.26L TML-6 DesignPart 2 of 4 Motion Compensation: Multiple reference pictures (per H.263++ Annex U) B picture support (per several prior standards) Multihypothesis concept being evaluated 1/4 sample accuracy motion (sort of per MPEG-4, could possibly go to 1/8 pel) 6x6 tap filtering to 1/2 sample accuracy, bilinear filtering to 1/4 sample accuracy Various block sizes and shapes for motion compensation (7 segmentations of the macroblock) “Funny position” with heavier filtering Affine motion under consideration

26. The H.26L TML-6 DesignPart 3 of 4 Intra Coding Structure: Directional spatial prediction (6 types for luma, one for chroma) Alterations under consideration Transform Variable block size for intra (16x16, 8x8, 4x4) Technically not exactly a DCT, but an integer transform closely approximating a DCT Based primarily on 4x4 transform size (all prior standards used 8x8) Expanded to 8x8 for chroma by 2x2 DC transform Adaptive block size under consideration

27. The H.26L TML-6 DesignPart 4 of 4 Two inverse scan patterns Logarithmic step size control Smaller step size for chroma (per H.263 Annex T) Universal variable-length coding (configurability under consideration) Adaptive arithmetic coding under strong consideration In-loop deblocking filter Distinct Network Adaptation Layer (NAL) design for network transport Inter-sequence transitional pictures under consideration

28. Future Work in MPEG MPEG to assess new video technology and address digital cinema needs Calls for proposals issued Tests to be conducted in next few months ITU-T VCEG bringing H.26L as reference Exploring potential future cooperative work between VCEG and MPEG

32. Windows Media TechnologiesVideo-Related Features WMV 8 Codec: A big step forward in compression performance Screen Codec: Outstanding compression (near) Lossless ! 640 x 480, 10 Fps < 20 Kbps (modem) 800 x 600, 15 Fps < 45 Kbps (ISDN/LAN) Advanced Streaming Format (ASF) file format Digital Rights Management (DRM): Critical for Content Providers

33. Future Trends Prediction is difficult - especially of the future. – Bohr (1885-1962) If we do not succeed, then we run the risk of failure. – Quayle (Phoenix Rep. Forum, 1990)

34. Principles of Rate-DistortionTheory Errors using inadequate data are much less than those using no data at all. – Charles Babbage (1792-1871) A little inaccuracy sometimes saves tons of explanation. – Saki (H.H. Munro, 1870-1916, The Comments of Moung Ka)

35. On Rate-Distortion Optimization Rate-distortion optimization and searching techniques will increase in importance Most enhancements take the form of an expanded range of choices More choices implies more need for searching and optimization Lagrange multiplier optimization provides an understandable, straightforward framework Recent understanding of coupling of step size and Lagrange multiplier makes it straightforward

36. Some Future Projections Coding Efficiency will continue to improve (Proof by existence): 4x4 coding Long-term memory Enhanced motion accuracy Enhanced motion models Enhanced intra coding People continue to come up with good ideas (and relatively predictable ones!)

37. What Area will Yield the Most Improvement? Although “prediction is difficult”, it is the area that will yield the most performance improvement Today’s coded motion model is primitive Several motion model improvement areas have yet to be fully exploited Waveform difference coding gain is limited

38. Won’t This be Unnecessary when Megabits become free? The need for better compression will not be reduced Got more bits? Give me higher resolution. Got more bits? Give me more channels. Improving worth effort? 20% of a lot is a lot. Bit rates have a slower doubling time than computing power.

39. Increasing “Layers” of Standardization In olden days: Design a system for a network with a video coder as part of that system design. Now: Standardize a “language” of syntax with maximum flexibility and a rich feature set Standardize how to configure the standard Standardize how to encapsulate the standard data on a network Standardize digital rights management for the data Standardize the system to carry the data

40. Other Kinds of Layers Continuing interest in Layered coding: Scalability in MPEG-2, H.263+, and MPEG-4 Layered coding ongoing work (Microsoft, MPEG Enhanced FGS) Mixed success toward products Motivation 1: The bit-rate scalability dream Motivation 2: The limitations of resolution Motivation 3: The error resilience need

41. Conclusions There will be plenty of need for further work. There will be plenty of need for more processing power. There will be plenty of need for more bits. There will be plenty of need for good ideas. And those good ideas will come. Dream no small dreams, for they have no power to move the hearts of men. - Goethe (1749-1842)