1. MPEG & MP3 -supplement - from “ Graham McAllister - Nortel Networks ”

2. TechniqueCompression Ratio When? Huffman1.5-2:11952 RLE4-10:11966 LZW2-10:11977&84 Quadtree2:11980 VQ10:11984 Directional Filtering 10-40:11985 Fractals10-1000:11988 MPEG-110-100:11993 Surface Methods 10-50:11995 MPEG-210-200:11995 MPEG-410-500:11999 time

3. MPEG Today MPEG-2 –Super-set of MPEG-1 –Rates up to 10 Mbps (720x486) –Can do HDTV (no MPEG-3) MPEG-4 –Around Objects, not Frames –Lower bandwidth MPEG-7 –Not (yet) a standard –Allows content-description (ease of searching) MPEG-21 MP3 –For audio –MPEG-1 Layer-3

4. Digital video formats MPEG / MJPEG Files with a.mpg extension Apple QuickTime Files with a.mov or.qt extension Microsoft AVI Files with a.avi extension Real Player Files with a.rm extension

7. 1. Image Sequence Compression Uses Inter-frame encoding Also known an image sequence or temporal coding

8. Temporal Redundancy Reduction

9. MPEG Process How does it work? 1. Sub-sample Reduces data by around 50% RGBYUV luminance

10. MPEG Process II 2. Motion Detection – on luminance block only three types of frame … I Frames – intra-coded P Frames – prediction from previous frame B frames – use bi-directional prediction 1 I 2 B 3 B 4 P 5 B 6 P 7 B 8 I

11. Example sequence transmitted as I P B B I B B Frame 1Frame 2Frame 3Frame 4Frame 5Frame 6Frame 7 I frameB frame P frameB frame I frame MPEG compression Forward prediction Bidirectional prediction Compressed stream Input stream

12. 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

13. Motion Prediction

14. Motion Estimation

15. Motion Estimation (cont ’ d)

16. Temporal Redundancy Reduction I frames are independently encoded P frames are based on previous I, P frames B frames are based on previous and following I and P frames –In case something is uncovered

17. MPEG Process III - Schematic Image Sequences RGB To YUV Motion Estimation DCT QuantizeRLEVLC Output Buffer No compression achieved

18. MPEG-1 & MPEG-2 MPEG-1 –Designed for video playback at 150KB/s - single speed CD-ROM –Used in VCD technology MPEG-2 –Much higher bandwidth – 3MB/s –DVD technology

19. MPEG-4 Very different from previous generations Aimed at low-bandwidth applications – at upper end, good enough for digital TV Digital Camcorders

20. MPEG-4 II - Meshes 2-D animated meshes Textures mapped onto meshes Store vertices of mesh and movement parameters

21. MPEG-4 III - Sprites MPEG-4 is object based – state of the art Panoramic images – massive compression ratios – 1000:1

22. 2. Audio Compression Techniques from image compression can be used –Huffman encodes output –DCT MP3 – huge!!!!

23. MP3 – MPEG-1 Layer 3 1. Minimal Audition Threshold –Don ’ t store anything under 5Khz 2. Masking Effect –Uses psychoacoustic model of the ear –Don ’ t store quiet and loud noises simultaneously

24. MP3 II 3. Joint Stereo (JS) coding –1. Intensity Stereo (IS) Ear unable to locate some frequencies – bass Store signal in mono + minimum for spatialization –2. Mid/Side (MS) Stereo Used if left and right speakers are similar Store middle (L+R) plus a side speaker (L or R) e.g. LR 105 75Store: Raw: Fewer bits Decompress:105

25. MP3 III - schematic