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Media Compression

Explore the world of media compression, from JPEG to MPEG video compression techniques. Learn how compression reduces file sizes for efficient bandwidth and storage utilization. Uncover the secrets behind Discrete Cosine Transform, Color Sub-sampling, Differential Coding, Run-Length Encoding, and more. Dive into the concepts of Temporal Redundancy, Motion Estimation, and Bi-directional Prediction in video compression. See the intricate decoding processes involved in MPEG structures, from I-Frames to B-Frames. Discover the technology behind Motion JPEG and the reduction ratios achieved in video compression. Whether you are a beginner or a tech enthusiast, this comprehensive guide will deepen your understanding of media compression.

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Media Compression

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  1. Media Compression

  2. You are Here Encoder Decoder Middlebox Receiver Sender Network

  3. Why compress? • “Bandwidth Not Enough” • “Disk Space Not Enough” • Size of Uncompressed DVD Movie =

  4. Why compress? • “Bandwidth Not Enough” • “Disk Space Not Enough” • Size of Uncompressed DVD Movie = 720 x 576 x 3 x 25 x 60 x 120 =208.6GB

  5. JPEG Compression

  6. Original Image (1153KB) 1:1

  7. Original Image (1153KB) 3.5:1

  8. Original Image (1153KB) 17:1

  9. Original Image (1153KB) 27:1

  10. Original Image (1153KB) 72:1

  11. Original Image (1153KB) 192:1

  12. Compression Ratio

  13. Magic of JPEG • Throw away information we cannot see • Color information • “High frequency signals” • Rearrange data for good compression • Use standard compression

  14. Discard color information Y V U

  15. Color Sub-sampling 4:4:4 4:2:0 4:2:2 4:1:1

  16. 4:2:2 Sub-sampling Y V U

  17. Original Image (1153KB) 4:2:0

  18. Original Image (1153KB) “4:1:0”

  19. Discrete Cosine Transform Demo

  20. Quantization DC 242 65 23 5 8 8 8 8 30 8 2 0 -54 -10 -4 -2 8 8 8 16 -6 -1 0 0 / = 13 6 3 5 8 8 16 32 1 0 0 0 2 1 -1 -2 8 16 32 64 0 0 0 0 Quantization Table AC

  21. -5 30 30 27 2 25 8 3 3 3 3 8 2 1 1 1 1 2 0 0 0 0 0 0 2 6 6 2 2 2 1 1 -1 -1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 1 4 4 4 4 1 0 0 0 0 0 0 1 1 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Differential Coding

  22. 27 3 1 0 2 1 0 0 4 0 1 0 0 0 0 0 Zig-zag ordering 27, 3, 2, 4, 1, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0

  23. 27 3 1 0 2 1 0 0 4 0 1 0 0 0 0 0 Run-Length Encoding 27, 3, 2, 4, 1, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0 (27, 1) (3, 1) (2, 1), (4, 1), (1, 2), (0, 5), (1, 1), (0, 4)

  24. Idea: Motion JPEG • Compress every frame in a video as JPEG • DVD-quality video = 208.6GB • Reduction ratio = 27:1 • Final size = 7.7GB

  25. Video Compression

  26. Temporal Redundancy

  27. Motion Estimation

  28. Bi-directional Prediction

  29. Watch for Motion Vectors Demo

  30. H.261 P-Frame I-Frame

  31. MPEG-1 B-Frame

  32. MPEG Frame Pattern • Example display sequence: • IBBPBBP … • Example encoding sequence: • IPBBPBB

  33. Compression Ratio

  34. Sequence • sequence header: • width • height • frame rate • bit rate • :

  35. GOP: Group of Picture • gop header: • time • :

  36. Picture • pic header: • number • type (I,P,B) • :

  37. Picture

  38. Slice

  39. Macroblock

  40. Y Y Y Y Block U 1 Macroblock = V

  41. For I-Frame • Every macroblock is encoded independently (“I-macroblock”)

  42. For P-Frame • Every macroblock is either • I-macroblock • a motion vector + error terms wrt a prev I/P-frame (“P-macroblock”)

  43. For B-Frame • Every macroblock is either • I-macroblock • P-macroblock • a motion vector + error terms wrt a future I/P-frame • 2 motion vectors + error terms wrt a prev/future I/P-frame

  44. Review: MPEG structure • Sequence • GOP • Picture • Slice • Macroblock • Block

  45. MPEG Decoding (I-Frame) Entropy Decoding Dequantize 101000101 IDCT

  46. MPEG Decoding (P-Frame) Entropy Decoding Dequantize 101000101 IDCT Prev Frame +

  47. MPEG Decoding (B-Frame) Entropy Decoding Dequantize 101000101 Future Frame IDCT AVG Prev Frame +

  48. There are more.. • Half-pel Motion Prediction • Skipped Macroblock • etc.

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