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MPEG-2 Digital Video Coding Standard

MPEG-2 Digital Video Coding Standard. Dihong Tian dhtian@ece.gatech.edu http://users.ece.gatech.edu/dhtian ECE 8873 – Data Compression and Modeling Georgia Institute of Technology. Outline. Overview MPEG audio (brief introduction) MPEG-2 video coding Basic building blocks

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MPEG-2 Digital Video Coding Standard

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  1. MPEG-2 Digital Video Coding Standard Dihong Tian dhtian@ece.gatech.edu http://users.ece.gatech.edu/dhtian ECE 8873 – Data Compression and Modeling Georgia Institute of Technology

  2. Outline • Overview • MPEG audio (brief introduction) • MPEG-2 video coding • Basic building blocks • Profiles and Levels • Coding interlaced video • Scalable coding extensions • Other features • Summary D.-H. Tian @ ECE-8873

  3. What does MPEG define? • MPEG defines the protocol of the bitstream between the encoder • and the decoder • The decoder is defined by implication; the encoder is left very much • to the designer D.-H. Tian @ ECE-8873

  4. MPEG-2 – Why another standard? • MPEG-1 (1988 - 1993) • Medium bandwidth (up to 1.5Mbits/sec) • 1.25Mbits/sec video 352 x 240 x 30Hz • 250Kbits/sec audio (two channels) • Non-interlaced video • Optimized for CD-Rom • MPEG-2 (1990 - 1995) • Multi-channel surround sound coding • Higher bit rates (up to 80 Mbits/sec) • A larger number of applications (SDTV, HDTV, etc) • The encoding standard is a toolkit • Interlaced and non-interlaced frame • Different color subsampling modes e.g., 4:2:2, 4:2:0, 4:4:4 • Flexible quantization schemes – can be changed at picture level • Scalable bit-streams • Profiles and levels • Backward compatible D.-H. Tian @ ECE-8873

  5. MPEG Audio • Digital audio compression part of MPEG uses auditory masking techniques. • MPEG-1 audio (ISO/IEC IS 11172-3) specifies mono or two-channel audio which may be Dolby Surround coded at bit rates from 32 kb/s to 384 kb/s. • MPEG-2 audio (ISO/IEC IS 13818-3) specifies up to 7 channels (but 5 is more common), rates up to 1 Mb/s and supports variable bit-rate as well as constant bit-rate coding. MPEG-2 handles backward compatibility by encoding a two-channel MPEG-1 stream, then adds the 5/7 audio as an extension. D.-H. Tian @ ECE-8873

  6. MPEG Video Coding - Fundamentals • Source model • Inter-pel correlation • Spatial correlation • Temporal correlation • Subsampling and Interpolation • Spatial domain (YUV components: 4:2:0, 4:2:2, ……) • Temporal domain (frame rate) • Basic building blocks: • Temporal prediction (Motion Compensated prediction) • Frequency domain decomposition (DCT) • Quantization • Variable-length coding D.-H. Tian @ ECE-8873

  7. Hierarchy • Sequence layer • GOP layer • Picture layer • Slices • Macroblock • Block (8x8 pixels) I-, P-, or B-type 16 x 16 pixels 16 x 16 pixels Frequency domain decomposition Variable length coding Quantization Motion compensated prediction

  8. Video Stream Data Hierarchy D.-H. Tian @ ECE-8873

  9. Recap • Overview • MPEG audio (brief introduction) • MPEG-2 video coding • Basic building blocks • Profiles and Levels • Coding interlaced video • Scalable coding extensions • Other improvements D.-H. Tian @ ECE-8873

  10. Profiles & Levels • Profile: A collection of compression tools that make up a coding system • Level: Picture source format ranging from about VCR quality to full HDTV Scalable coding available Coding interlaced video A straightforward extension of MPEG-1

  11. Coding Interlaced Video • Interlaced video (TV) vs. Progressive video • Each frame consists of two interlaced fields First field: odd-numbered lines of the frame (top field) Second field: even-numbered lines of the frame (bottom field) • Display device interlaces the fields to composite a frame • TV in Europe: Frame rate 25 Hz => Field rate 50 Hz TV in America: Frame rate 30 Hz => Field rate 60 Hz • MPEG-2 supports: • Two picture formats: frame-picture and field-picture • Field/frame DCT option per MB for frame pictures • New MC prediction modes for interlaced video D.-H. Tian @ ECE-8873

  12. New Picture Types for Interlaced Video • Frame pictures (I, P, or B type) • Field pictures (I, P, or B type) D.-H. Tian @ ECE-8873

  13. Field/Frame DCT Option for Frame Pictures In a frame picture, mpeg-2 allows a field- or frame-DCT option for each macroblock • High motion – field-DCT • No motion, high spatial activity – frame-DCT D.-H. Tian @ ECE-8873

  14. Prediction Modes in MPEG-2 • Field prediction: made independently for each field from previously decoded field(s) • Frame prediction: made from previously decoded frame(s) • (16x8) motion compensation (only used in field pictures): 2 motion vectors used for each MB • Dual-prime prediction (only used for P-pictures): made from 2 reference fields which are averaged to form the final prediction D.-H. Tian @ ECE-8873

  15. Scalable Coding General philosophy • Support applications beyond those addressed by the basic MAIN profile coding algorithm • Scalable coding schemes: SNR scalability / Spatial scalability / Temporal scalability • Up to three different scalable layers D.-H. Tian @ ECE-8873

  16. SNR-Scalable Video Encoder D.-H. Tian @ ECE-8873

  17. Spatial-Scalable Video Coder D.-H. Tian @ ECE-8873

  18. Temporal Scalability D.-H. Tian @ ECE-8873

  19. Other Features in MPEG-2 • Alternate scan – fit interlaced video better Zig-Zag Scan Alternate Scan D.-H. Tian @ ECE-8873

  20. Other Features in MPEG-2 (cont’d) • Finer quantization of the DCT coefficients • Intra macroblock • DC coefficients: 11 bits (full) resolution vs. 8 bits in MPEG-1 • AC coefficients: [-2048, 2047] vs. [-256, 255] in MPEG-1 • Non-intra macroblock • [-2048, 2047] vs. [-256, 255] in MPEG-1 • Finer adjustment of MQUANT scaling parameter MPEG-1: integers (1-31) MPEG-2: an optional set including real numbers from 0.5 to 56 D.-H. Tian @ ECE-8873

  21. Summary • MPEG-2 allows higher bit rates than MPEG-1 • MPEG-2 supports a larger number of applications • MPEG-2 allows surround sound, and alternative language channels • MPEG-2 allows progressive sequences and interlaced sequences • MPEG-2 allows alternative scan patterns other than the zig-zag pattern • MPEG-2 has scalable coding extensions, including: • SNR scalability • Spatial scalability • Temporal scalability D.-H. Tian @ ECE-8873

  22. References [1] Http://www.mpeg.org [2] John Watkinson, “MPEG-2”, Focal Press, 1999. [3] P. N. Tudor, “MPEG-2 video compression”, IEEE Electronics & Communication Engineering Journal, Dec. 1995. [4] T. Sikora, “MPEG digital video coding standards”, IEEE Signal Processing Magazine, Sept. 1997. [5] A. M. Tekalp, “Digital video processing”, Prentice Hall, 1998. D.-H. Tian @ ECE-8873

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