Error Resilience in a Generic Error Resilience in a Generic Compressed Video Stream Compressed Video Stream

Transmitted over a Wireless ChannelTransmitted over a Wireless Channel

Muhammad BilalMuhammad Bilal

2005-06-00202005-06-0020

Channel NoiseChannel Noise

Markov Process ModelMarkov Process Model AWGN ModelAWGN Model Transfer Function ModelTransfer Function Model

Hata Model, Akumura ModelHata Model, Akumura Model

Error Correction MethodsError Correction Methods

RedundancyRedundancy Header informationHeader information Motion VectorsMotion Vectors DC coefficientDC coefficient

Source Coding Source Coding Reed SolomonReed Solomon Hamming CodeHamming Code

Channel EqualizationChannel Equalization Channel codingChannel coding Channel responseChannel response

Error LocalizationError Localization

Reversible Variable Length CodesReversible Variable Length Codes Fixed Synchronization MarkersFixed Synchronization Markers

Error Resilience Methods Error Resilience Methods

Data PartitioningData Partitioning SNR scalabilitySNR scalability PredictionPrediction

– Intra coded frameIntra coded frame Copy previous blockCopy previous block DC coefficient predictionDC coefficient prediction

– Inter coded frameInter coded frame Motion Vector Data based predictionMotion Vector Data based prediction

FrameworkFramework

A generic video compressorA generic video compressor– MATLAB implementationMATLAB implementation– ‘‘MPEG-2 like’ bit streamMPEG-2 like’ bit stream– Platform for video coding analysisPlatform for video coding analysis

Compression efficiencyCompression efficiency Motion Estimation (offset distortion)Motion Estimation (offset distortion) Data PartitioningData Partitioning EtcEtc

– Demonstration of good quality & highly Demonstration of good quality & highly quantized videosquantized videos

Error Introduction MethodsError Introduction Methods

Arbitrary bursts of error in bit streamArbitrary bursts of error in bit stream– Header lossHeader loss– RVLC synchronization problemRVLC synchronization problem– Need to deal with resynchronizationNeed to deal with resynchronization

Error Introduction Methods Error Introduction Methods (contd.)(contd.)

Intelligent error introduction Intelligent error introduction (Macroblock (Macroblock level)level)

– Assume bit stream remains synchronizedAssume bit stream remains synchronized– Error in coefficients/motion vector dataError in coefficients/motion vector data– SNR degradationSNR degradation– DemonstrationDemonstration

Error propagation due to motion compensationError propagation due to motion compensation Need for ‘I’ frame GDR (Gradual Data Refresh)Need for ‘I’ frame GDR (Gradual Data Refresh)

Quality MeasuresQuality Measures

Subjective evaluationSubjective evaluation SNRSNR

– Deceiving results for some sequencesDeceiving results for some sequences

AnalysisAnalysis

Effect of various error concealment Effect of various error concealment methodsmethods

– I FramesI Frames DC Coefficients savedDC Coefficients saved

– ‘‘D’ frameD’ frame

DC Coefficients not savedDC Coefficients not saved– Copy previous frame blockCopy previous frame block

Error propagation due to motion Error propagation due to motion compensationcompensation

Analysis Analysis (contd.)(contd.)

‘‘P’ FramesP’ Frames– Dependent on ‘I’ frame (error Dependent on ‘I’ frame (error

propagation)propagation)– Dependent on contentDependent on content

High motion content (Foreman)High motion content (Foreman) Head & Shoulder (News)Head & Shoulder (News) Camera panning (Coastguard)Camera panning (Coastguard)

– Motion Vector Data + DCTMotion Vector Data + DCT DCT data useless without MVDCT data useless without MV MV data useful without DCT dataMV data useful without DCT data demonstrationdemonstration

Analysis Analysis (contd.)(contd.)

‘‘P’ FramesP’ Frames– Absence of DCT dataAbsence of DCT data

Copy motion compensated blockCopy motion compensated block Previous frame non MC block degrades video Previous frame non MC block degrades video

for high motion contentfor high motion content

Analysis Analysis (contd.)(contd.)

‘‘P’ FramesP’ Frames– Dependency on ‘I’ framesDependency on ‘I’ frames– Perfect ‘I’ frame decodingPerfect ‘I’ frame decoding

DCT data destroyedDCT data destroyed MV data availableMV data available DemonstrationDemonstration

– Seamless video (news)Seamless video (news)– Acceptable video for many purposes Acceptable video for many purposes (coastguard, (coastguard,

foreman)foreman)

Analysis Analysis (contd.)(contd.)

Critical DataCritical Data– I FrameI Frame

DC coefficientsDC coefficients

– P FrameP Frame I frameI frame MV dataMV data Motion Estimation algorithmMotion Estimation algorithm

– Attempt to find the ‘actual’ motion vectorAttempt to find the ‘actual’ motion vector

SNR vs BERSNR vs BER

News

05

10152025303540

0.000351 0.001 0.001754

Bit error Rate

SN

R

Only DC coefficientsaved

Whole I framereconstructed

SNR vs BERSNR vs BER

Foreman

0

5

10

15

20

25

30

35

0.000351 0.001 0.001754

Bit error Rate

SN

R

Only DC coefficientsaved

Whole I framereconstructed

SNR vs BERSNR vs BER

Coastguard (76th frame)

0

5

10

15

20

25

30

0.000351 0.001 0.001754

Bit error Rate

SN

R

Only DC coefficientsaved

Whole I framereconstructed

SNR vs BERSNR vs BER

Comparison

05

10152025303540

0.000351 0.001 0.001754

Bit error Rate

SN

R

News

Foreman

Coastguard

ConclusionConclusion

Error ResilienceError Resilience– Error localizationError localization

ParityParity Hamming CodesHamming Codes

– RedundancyRedundancy DC coefficients + MV dataDC coefficients + MV data I frame perfect decoding (BW demanding)I frame perfect decoding (BW demanding)

– Compensate with more number of P frames in Compensate with more number of P frames in GOPGOP

Conclusion Conclusion (contd.)(contd.)

Data PartitioningData Partitioning– Critical data positioned close to Critical data positioned close to

resynchronization markerresynchronization marker DC coefficients in ‘I’ framesDC coefficients in ‘I’ frames MV data in ‘P’ framesMV data in ‘P’ frames

Conclusion Conclusion (contd.)(contd.)

Further compression!Further compression!– Randomly introduce ‘not coded’ blocksRandomly introduce ‘not coded’ blocks

Depend on decoder error concealment Depend on decoder error concealment schemescheme

Infrequent ‘not coded’ blocks will result in Infrequent ‘not coded’ blocks will result in seamless video decodingseamless video decoding

Q&AQ&A