Technion IIT Dept. of Electrical Engineering

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Technion - IITDept. of Electrical Engineering
Signal and Image Processing lab
Transrating and Transcoding of Coded Video
Signals
David Malah Ran Bar-Sella Michael
Lavrentiev
STRIMM Meeting June 25, 2003
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Cell-phone
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H.264 Intra Spatial Prediction
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• Frame dropping (B, P)
• Color suppression
• Discarding high-frequency DCT coefficients
• Reducing spatial resolution (size reduction)
• DCT coefficients Re-quantization

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• Related Issues
• Open Loop
• Closed Loop
• - Pixel-Domain
• - DCT-Domain

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(Werner 1997)
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Re-quantization Error
Q2
Original pixel value
Quantized values with Q1
Quantized values with Q2
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(Assuncao and Ghanbari, 1997)

• Recent result (Laventer and Porat ICIP-03)
  Optimal quantizer steps
• are obtained at values close to specific
  multiples of the input quant. step.

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Variable Length Coding
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Macro-Block
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• Video frames can be partitioned (segmented) into
  regions
• having different characteristics
• Textured regions
• Smooth regions
• Edges
• Moving objects

• Different regions have different perceptual
  importance and
• may be encoded at different rates for similar
  subjective quality.

• For efficiency, segmentation should be based on
  compressed-
• domain data Block DCT Coeff., MB type, MB
  q-step, MB rate,
• and Motion Vectors (MV).

• Possible approach Block classification,
  Region-growing, and
• Segment tracking.

• Bit allocation to each region should reflect
  perceptual importance.

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H.264 Main Differences vis-à-vis MPEG-2

• MEC
• - 7 modes (block sizes 16x16 4x4)
• ¼ Pel resolution
• Improved MV coding
• Transform
• Integer transform (4x4)
• Intra Prediction
• spatial prediction (9 modes)
• 16x16 or 4x4 blocks
• Inter Prediction
• Multiple reference frames (1 5)
• SP frame for stream transition

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I. Transrating (MPEG2 ? MPEG2)

• Re-quantization
• Restricted Lagrangian optimization with MSE /
  MAP
• Trellis re-quantization (MSE optional)
• Bit-rate Control
• Integrating other rate-reduction techniques
• (temporal and spatial resolution reduction
  BGU)

• HVS-based bit-rate reduction
• Frame segmentation and tracking
• HVS-based bit allocation to segments
• Restricted Lagrangian optimization in each
  segment
• Trellis re-quantization in each segment

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II. Transcoding (MPEG-2 ? H.264)

• Base-line Transcoder
• Maximum matching to MPEG-2
• MEC MB based ½ pixel res.
• BP frames, Single ref. frame
• No Intra spatial prediction
• Same MB types decisions
• Adapted H.264 features
• Syntax
• UVLC
• Transform
• Quantization

• Reduced rate
• Adapting developed
• re-quantization techniques
• from MPEG-2
• Integrating other rate-
• reduction techniques
• (temporal and spatial
• resolution reduction BGU)

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