MPEG-1%20and%20MPEG-2%20Digital%20Video%20Coding%20Standards

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MPEG-1 and MPEG-2 Digital Video Coding Standards

• Author Thomas Sikora
• Presenter Chaojun Liang

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Overview

• Introduction
• Intra-picture Coding Techniques
• Inter-picture Coding Techniques

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What is MPEG?

• Stands for Moving Picture Expert Group
• Nickname to a family of International standards
  used for coding audio-visual information in a
  digital compressed format.
• Includes MPEG-1, MPEG-2, and upcoming MPEG-4.

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MPEG-1

• Finalized in 1991
• Optimized to work at 352240, 30 f/s or 352288,
  25f/s
• Bit-rate is optimized for application of around
  1.5 Mb/sec
• Defined for progressive frames only

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MPEG-2

• Finalized in 1994
• Digital television broadcasting
• Target bit-rate raised to 4-9Mb/sec
• Main Profile, Main Level
• 720480 pixels, 30 frame/sec, 15Mb/sec
• Main Profile, High Level (HDTV)
• 19201280 pixels, 30 frame/sec, 80Mb/sec

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MPEG Video Layers
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Intra Frame Coding Techniques
Bit-Rate Control
Video Filter
Run-length Encoding
Bitstream Buffer
DCT
Quantizer
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Video Filter

• Subjective Redundancy
• Eyes more sensitive to changes in Luminance, less
  to variations in Chrominance
• R G B -gt Y Cb Cr
• Sample Chrominance 21 in both directions

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Video Filter
Color Space Transform
Sample
R G B
Y Cb Cr
Y Cb Cr
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Statistical Redundancy
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Discrete Cosine Transform

• Closely related to Discrete Fourier Transform
• Performed on 88 block

Forward DCT
Inverse DCT
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DCT Basis Patterns
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DCT Basis Patterns
Increasing Vertical Frequency (Down)
Increase Horizontal Frequency (Right)
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Variance Distribution of DCT Coefficients
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DCT Coefficient Quantization

• Higher frequency -gt Larger step size -gt more
  coarsely quantized
• Force as many of the DCT-Coefficients as possible
  to zero or near zero

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Example Coefficients
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Run-Length Encoding
Run-Amplitude Pairs
Bit Stream
Variable Length Code Table
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Inter Frame Coding Techniques

• Exploit temporal redundancy
• Use Motion Estimation to eliminate temporal
  redundancy

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Picture Types

• Intra Pictures (I-Pictures)
• Predicted Pictures (P-Pictures)
• Bi-directional Pictures (B-Pictures)

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Intra Pictures

• Coded with only info in the picture itself
• Random access points into the compressed data
• Moderate compress about 2 bits per coded pixel

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Predicted Pictures

• Coded with respect to the nearest previous
  I-Picture or P-Picture

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Bi-directional Pictures

• Use both a past and future picture as a reference.

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Video Stream Composition

• Encoder chose frequency and location of
  I-Pictures
• Typical display order

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Video Stream vs Display order
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Motion Estimation
Tree moved down to the right
People moved farther to the right than tree
Frame 1
Frame 2
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Motion Estimation

• To adequately represent the change, or the
  difference, between 2 video frames
• Frame-wise direct minus not effective
• Macroblock-wise minus
• 2-D spatial search for each luminance macroblock

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Macroblock Matching
Frame 1
Frame 2
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Picture 1
Picture 2
Predicted Picture
Residual Error Picture
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Coding of Residual Errors

• Similar to Intra frame coding
• Different quantization matrix
• Motion vectors are also coded

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