Rate-distortion Optimized Mode Selection Based on Multi-channel Realizations

1
Rate-distortion Optimized Mode Selection Based on
Multi-channel Realizations

• Markus Gärtner
• Davide Bertozzi
• Classroom Presentation
• 13th March 2001

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Overview

• Hybrid Video Coding
• Proposed Architecture
• Multi-channel realizations
• Performance Measurements
• Concealment Techniques
• Number of Channel Realization
• Error Propagation
• Conclusions

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Motion-compensated hybrid coder
Intraframe DCT coder
IntraframeDecoder
Motion compensated predictor
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Proposed Improvements over H.263

• H.263 Hybrid Video Coder
• Error propagation in the decoder loop neglected
• Error-free transmission assumed
• Threshold based mode selection
• Goals of our approach
• Simulation of several channel conditions
• Prediction of the error incurred at the receiver
• Rate-Distortion optimized mode selection

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Multiple Channel Realizations
output
Coder
Frame Buffer
Decoder
Original Encoder
nth Channel Realization
input
Inter
Channel n
Decoder
Conceal-ment Mode Decision
Intra
Channel n
Decoder
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Channel Realizations

• Randomly generated error patterns for each
  channel
• Capture different sensitivity of macro-blocks to
  errors

X
Channel 1
X
Channel 2
X
Estimate of the real channel conditions (on the
average)
Channel n
X
X
Group of blocks (GOB)
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Error Concealment

• Bit error causes loss of macro block
• Synchronization markers before each GOB
• Macro block concealment
• GOB concealment
• Concealment of rest of GOB

Erroneous macro-blocks are replaced by respective
macro-block of previously reconstructed frame
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Distortion Measure
For each Macro-block
Channel 1
Channel N
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Mode Selection
Input Frame

• Decision takes place for each macro-block ?
  selection table
• Computational complexity

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Channel Decoder
Intra quantized frame
input
Coder
Inter difference signal, motion vectors
For each channel
Mode

• Inter previous frame buffer content difference
  signal
• Intra quantized frame

Selection table
Reconstructed Frame
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Experimental Setup
Quantizer
Encoder
Frame Buffer
Channel
Decoder
Dequantizer
Frame Buffer
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Performance Measurement (I)
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Performance Measurement (II)
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Number of Realizations
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Error Propagation (I)

• First I-Frame received in error

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Error Propagation (II)

• First I-Frame received correctly

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Conclusions

• Suitability for error-prone environments
• Better performance than H.263
• Reduction of error propagation
• Limitations
• Advanced modes of H.263 not considered
• Computational complexity
• Application for downloadable multimedia
• Future work
• Sophisticated channel models
• Implementation of advanced features