Video Compression Demystified - Intro to MPEG, AVI, WMV

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Introduction on need and method of video compression. Basics of it

Introduction on need and method of video compression. Basics of it

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  • 1. Video Compression Demystified Intro to MPEG, WMV, H.264, AVI
  • 2. Why compression?
    • Bandwidth constraint
    • Space constraint
    • I don’t know what else?
  • 3. Basic idea
    • Correlation (Entropy)
      • Space, Time, Bits
    • Human eye models
      • Low-pass filter
      • Brain ‘fills’ in for sharpness
    • Frugality
  • 4. Pixels and frames
    • Each picture is a set of pixels in two dimensions, third being time.
    • Finite sharpness, resolution issue.
    • Each group of 8 pixels = block
    • 2x2 blocks = Macroblock
  • 5. Correlation in space
    • Space is ‘gravitated’ towards being continuous.
    • How do you exploit it?
      • DCT inside a block
      • AC-DC prediction across blocks
  • 6. Correlation in Time
    • The WHOLE image does not change.
    • Do NOT repeat information.
    • Motion estimation
      • Locate where my marker is moving towards.
      • Send only the coded difference.
    • Bi-predict pictures.
  • 7. Correlation in bits
    • Run-level-last coding for zeroes.
    • Subsequent bits still have correlation in them.
    • Huffman coding (VLC)
    • Arithmetic coding (CABAC)
  • 8. Human eye
    • Eye is not responsive to every detail
      • Quantization
      • Smoothening filters
    • Eye is more responsive to brightness
      • Less effort of chrominance
    • Brain fills in crucial details.
  • 9. DCT and quantization
    • Random in Time domain is high freq.
    • Spatial redundancy reduced to a few significant values.
    • Zigzag coding + quantization
    • Focus on lower freq and suppress high freq.
  • 10. Motion Estimation
    • Find the best match around – ME
      • Diamond, Hierarchical, Logarithmic
      • Generally over a block.
    • Half-pel and quarter pel motion estimation using filters.
      • Better match in sub-pel level.
  • 11. RLL and Huffman
    • Long sequence of zeroes helps reducing to smaller chunks of data.
    • This chunk also has a probabilistic models.
    • Exploit probability of symbols and be frugal in bits.
    • Context adaptive arithmetic coding.
  • 12. MPEG
    • MPEG-1:
      • DCT
      • Pixel level ME
      • AC-DC prediction
      • P pictures
      • Huffman coding
  • 13. MPEG-4
    • DCT
    • Quarter-pel ME
    • B pictures
    • AC-DC prediction
    • Data partitioning
    • Objects – layers, groups, streams
  • 14. H.264
    • Integer transform on 4x4 block
    • Quarter pel ME on 4x4
    • In-loop de-blocking
    • Multiple reference pictures
    • CABAC – 2 times frugal
    • Bit-plane coding
  • 15. AVI
    • Audio Video Interleave format
    • One frame of video with equivalent audio frame(s)
    • Necessary information
      • Display info
      • Shit