MPEG-2

1
MPEG-2

• Scalability Support

Nimrod Peleg Update Dec.2000
2
MPEG-2 Target

• ...Generic coding method of moving pictures and
  associated sound for ...digital storage, TV
  broadcasting and communication...
• Dedicated for high quality services
• e.g. HDTV, Networked data services etc.
• Eveloped from CCIR-601, CCIR-648, JPEG, H.261 and
  MPEG-1 former standards

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MPEG-2 Btstream structure
Sequence
Sequence
Sequence
Seq. Hdr.
GOP
Seq. Ext.
GOP
Ext.User
GOP Header
Picture Data
Picture Data
Ext.User
Pic. Hdr.
Slice
Pic. Coding Ext.
Ext.User
Slice
Slice Header
Macroblock
Macroblock
Block
Macroblock Hdr.
Block
Block
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Scalability Modes

• SPATIAL SCALABILITY
• TEMPORAL SCALABILITY
• SNR SCALABILITY
• DATA PARTITIONING

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SNR Scalability

• Refinement of the DCT coeffs. encoded in base
  layer by the enhancement layer coeffs.
• Base layer containes coarser quantization then
  enhancement layer
• Only non intra quant. matrices are used in the
  enhancement layer
• Enhancement layer contains coded refinement DCT
  coeffs. and a small overhead

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SNR Scalability (Contd)

• DCT coeffs. in base layer are added to DCT
  coeffs. in enhancement layer
• The combined layer decoding process is identical
  to decoding of a non-scalable bitstream
• Different rate control for the 2 layers

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SNR Scalability Scheme
Lower Layer Code
VLC
Inverse Scan
Inverse Quant

Enahncement Layer Code
VLC
Inverse Scan
Inverse Quant
Decoded Samples
Inverse DCT
Motion Compensation
Frame Storage Memory
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Data Partitioning

• The bitsteam is split into 2 layers partition0,
  partition1
• The Priority Breakpoint (in sequence header)
  indicates which syntax elements are placed in
  partition0 which is the base or high priority
  partition

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Data Partitioning (Contd)

• The remainder of the bitstream is placed in
  partition1 which is the low priority partition
• Seq.,GOP,picture and slice headers are duplicated
  from partition0 to partition1
• VBV refers to the sum of the 2 partitions
• Partition0 contains sequence scalable extension

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Data Partitioning (Contd)

• No Data Partitioning

• Partitions for Priority Break Point 64

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Data Partitioning (Contd)

• Possible Breakpoints
• After slice header
• After macroblock address increment
• (macroblock header)
• Before coded block pattern (after Motion Vector)
• After any number of DCT coefficients (excluding
  one)