MPEG: A Video Compression Standard for Multimedia Applications Didler Le Gall

Goals Reduce the high cost of video compression codecs Resolve the critical problem of interoperability of equipment from different manufacturers Come up with a standard within 2 years

MPEG Stands for Moving Picture Experts Group (ISO-IEC) Started in 1988 Had to come up with a draft of the standard by 1990 Received MPEG Proposal from mostly commercial companies

MPEG (cont’d) MPEG-Video MPEG-Audio MPEG-System –Synchronization of audio and video

Requirements A Generic Standard Random Access Fast Forward/Reverse Searches Reverse Playback Audio Visual Synchronization Robustness to Errors

Requirements (cont’d) Coding/Decoding Delay Editability Format Flexibility Cost Tradeoffs

MPEG-VIDEO Compression Spacial Redundancy –Intraframe compression –DCT compression Temporal Redundancy (i.e. motion compression) –Interframe compression

Discrete Cosine Transform (DCT) – black 255 – white

DCT (cont’d) The 64 (8 x 8) DCT basis functions Superimpose multiples of these functions to simulate the original picture

DCT (cont’d) 0 – black 255 – white

DCT (cont’d)

Motion Compensation I-Frame –Independently reconstructed P-Frame –Forward predicted from the last I- Frame or P-Frame B-Frame –forward predicted and backward predicted from the last/next I-frame or P-frame Transmitted as - I P B B B P B B B

Motion Prediction

Motion Estimation

Motion Estimation (cont’d)

Conclusion Video quality better than VHS can be achieved with a bit rate of about 1.5 Mbits/s Does not handle higher resolution with small bit rate

References MPEG Notes by Dale Kolosna MPEG Compression Technique ( chemnitz.de/~jan/MPEG/HTML/mpeg_tech.html)