1. MPEG-2 Digital Video Coding Standard
Dihong Tian
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
March 31, 2004
D.-H. 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
March 31, 2004
D.-H. ECE-8873

4. MPEG-2 – Why another standard?
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 ( )
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
March 31, 2004
D.-H. ECE-8873

5. MPEG Audio
Digital audio compression part of MPEG uses auditory masking techniques.
MPEG-1 audio (ISO/IEC IS ) 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 ) 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.
March 31, 2004
D.-H. 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
March 31, 2004
D.-H. 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
March 31, 2004
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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
March 31, 2004
D.-H. ECE-8873

10. Scalable coding available
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
Profile
Algorithms
HIGH
Supports all functionality provided by the Spatial Scalable Profile plus the
provision to support 3 layers with the SNR and Spatial scalable coding modes
4:2:2 YUV-representation for improved quality requirements
SPATIAL Scalable
Supports all functionality provided by the SNR Scalable Profile plus an
algorithm for spatial scalable coding (2 layers allowed)
4:2:0 YUV-representation
SNR Scalable
Supports all functionality provided by the MAIN Profile plus an algorithm for
SNR scalable coding (2 layers allowed)
MAIN
Non-scalable coding algorithm supporting functionality for:
coding interlaced video; random access; B-picture prediction modes
SIMPLE
Incudes all functionality provided by the MAIN Profile but does not support
B-picture prediction modes
Level
Parameters
HIGH
1920 samples/line
1152 lines/frame
60 frames/s
80 Mbit/s
HIGH 1440
1440 samples/line
60 Mbit/s
MAIN
720 samples/line
576 lines/frame
30 frames/s
15 Mbit/s
LOW
352 samples/line
288 lines/frame
4 Mbit/s
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
March 31, 2004
D.-H. ECE-8873

12. New Picture Types for Interlaced Video
Frame pictures
(I, P, or B type)
Field pictures
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D.-H. 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
March 31, 2004
D.-H. 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
March 31, 2004
D.-H. 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
March 31, 2004
D.-H. ECE-8873

16. SNR-Scalable Video Encoder
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17. Spatial-Scalable Video Coder
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18. Temporal Scalability
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19. Other Features in MPEG-2
Alternate scan – fit interlaced video better
Zig-Zag Scan
Alternate Scan
March 31, 2004
D.-H. 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
March 31, 2004
D.-H. 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
March 31, 2004
D.-H. 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
[4] T. Sikora, “MPEG digital video coding standards”, IEEE Signal Processing Magazine, Sept
[5] A. M. Tekalp, “Digital video processing”, Prentice Hall, 1998.
March 31, 2004
D.-H. ECE-8873

23. Questions