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MPEG: A Video Compression
Standard for Multimedia
Applications
Václav Hlaváč
CTU Prague, hlavac@cmp.felk.cvut.cz

Initial material were slides of Didier Le
Gall, Worcherster Polytechnic Institute.

Introduction
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•
•

2

1980’s technology made possible full-motion video
over networks
– Television and Computer Video seen moving
closer
– (Today, Sony and Microsoft are squaring off)
Needed a standard
– Often, triggers needed volume production
• Ala facsimile (fax)
– Avoid de facto standard by industry
1988, Established the Motion Picture Experts Group
(MPEG)
– Worked towards MPEG-1
– Primarily video but includes audio (MP3)

The Need for Video Compression

• High-Definition Television (HDTV)
– 1920x1080
– 30 frames per second (full motion)
– 8 bits for each three primary colors (RGB)

•

Total 1.5 Gb/sec!
Cable TV: each cable channel is 6 MHz
– Max data rate of 19.2 Mb/sec
– Reduced to 18 Mb/sec w/audio + control …
Compression rate must be ~ 80:1!

3

Compatibility Goals
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1990: CD-ROM and DAT key storage devices
– 1-2 Mbits/sec for 1x CD-ROM
Two types of application videos:
– Asymmetric (encoded once, decoded many times)
Video games, Video on Demand
– Symmetric (encoded once, decoded once)
• Video phone, video mail …
(How do you think the two types might influence
design?)
Video at about 1.5 Mbits/sec
Audio at about 64-192 kbits/channel

Requirements
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Random Access, Reverse, Fast Forward, Search
– At any point in the stream (within ½ second)
– Can reduce quality somewhat during this task, if
needed
Audio/Video Synchronization
Robustness to errors
– Not catastrophic if some bits are lost
– Lends itself to Internet streaming
Coding/Decoding delay under 150 ms
– For interactive applications
Ability to Edit
– Modify/Replace frames

Relevant Standards
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• Joint picture Experts Group (JPEG)
•
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– Compress still images only
Expert Group on Visual Telephony (H.261)
– Compress sequence of images
– Over ISDN (64 kbits/sec)
– Low-delay
Other high-bandwidth “H” standards:
• H21 (34 Mbits/sec)
• H22 (45 Mbits/sec)

MPEG Compression

• Compression through
– Spatial
– Temporal

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Spatial Redundancy

• Take advantage of similarity among most
neighboring pixels

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Spatial Redundancy Reduction
• RGB to YUV
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•
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– less information required for YUV (humans less
sensitive to chrominance)
Macro Blocks
– Take groups of pixels (16x16)
Discrete Cosine Transformation (DCT)
– Based on Fourier analysis where represent signal
as sum of sine...
MPEG: A Video Compression
Standard for Multimedia
Applications
Václav Hlaváč
CTU Prague, hlavac@cmp.felk.cvut.cz
Initial material were slides of Didier Le
Gall, Worcherster Polytechnic Institute.
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