Electrical Engineering National Central University Data Error in

Electrical Engineering National Central University Data Error in (Networked) Video M. K. Tsai 04 / 08 / 2003 Video-Audio Processing

Electrical Engineering National Central University Outline v what’s data error ? v cause of data error v kind of data error v effect of data error v resilience of data error v summary Video-Audio Processing

What’s Data Error ? Ø the data dealt with lossy processing F Q VLC Q-1 F-1 MC/ME Ø the data received in the decoder is different from that transmitted in the encoder Video-Audio Processing channel decoder Electrical Engineering National Central University

Cause of Data Error Ø channel § bit error、burst error、 packet loss § fading、multi-path、ISI、overflow in the router Ø process § lossy coding (ex: Q) § re-quantization (ex: drift) § DCT/IDCT mismatch (ex: SPDT) … § error concealment Video-Audio Processing Electrical Engineering National Central University

Kind of Data Error Electrical Engineering National Central University Ø channel § packet ü packet sequence number § header ü invalid code(ex: MBTYPE、MCBPC ……) § image data ü invalid code(ex: VLD、MV)、out of range(IDCT、MV) VLD MV Video-Audio Processing F-1 MC/ME Q-1

Effect of Data Error Electrical Engineering National Central University Ø packet loss § once errors found in a packet, it would be discarded Ø block/frame loss § once loss of synchronization happens at receiver, blocks or frames would be dropped § depend on the size of packet, packet loss may lead to block /frame loss Video-Audio Processing

Effect of Data Error Ø error propagation § VLD original bit error new § MV original new § Concealment original new Video-Audio Processing Electrical Engineering National Central University

Resilience of Data Error Ø channel § forward error correction (FEC) ü open loop error recovery method ü increase transmission overhead ü complicated decoding process ü not suitable for mobile network § automatic repeat request (ARQ) ü close loop error recovery method ü effective against burst error and packet loss ü more effective than FEC ü not realistic for real time transmission Video-Audio Processing Electrical Engineering National Central University

Resilience of Data Error Electrical Engineering National Central University Ø channel § error resilience tools ü resynchronization • marker is uniquely identifiable ü data partition (DP) • MVs and DCT coefficients are separated • correct data can be used for video reconstruction • If undetected errors occur in packets, received data can be considered invalid if boundary marker is’ t detected ü header extension code (HEC) • Important header information is repeated following HEC Video-Audio Processing

Resilience of Data Error Electrical Engineering National Central University Ø channel § error resilience tools ü reversible variable length coding (RVLC) • VLCs is uniquely decodable in both directions ü error concealment (EC) • highly dependent on the performance of the resynchronization scheme Video-Audio Processing

Resilience of Data Error Electrical Engineering National Central University Ø channel § Multiple Description coding (MDC) ü allow decoder to extract meaningful information from a subset of the bit stream ü encoder produce descriptions transmitted over channels Decode 0 MDC Encoder channel Decode 1 Decode 2 Video-Audio Processing

Resilience of Data Error Electrical Engineering National Central University Ø channel § error mitigation by feedback ü Reference Picture Selection (RPS) • reference picture is replaced adaptively according to the upstream messaging from the decoder • NACK is effective for low error rates, ACK is effective for high error rates ü Error tracking • use intra mode for MB severely distorted Video-Audio Processing

Resilience of Data Error Electrical Engineering National Central University Ø channel § packetization ü duplicate important information in multiple packet ü duplicate important packets ü how many packets per frame ü packetization delay Video-Audio Processing

Resilience of Data Error Electrical Engineering National Central University Ø channel § scalable coding with unequal error protection (UEP) ü SNR : by different quantization ü spatial : by different resolution ü temporal : by different frame rate § error confinement ü video object planes (VOP’s)coding ü independent segment decoding (ISD) Video-Audio Processing

Resilience of Data Error Electrical Engineering National Central University Ø channel § Error Resilient Entropy Coding (EREC) ü Convert VLCs to fixed-length blocks of data ü not guarantee image/video frame synchronization Video-Audio Processing

Resilience of Data Error Electrical Engineering National Central University Ø channel § video redundant coding ü picture sequences are assigned to more threads and each thread is coded independently Video-Audio Processing

Resilience of Data Error Electrical Engineering National Central University Ø process § error refreshment ü adaptive intra refresh (AIR) • avoid large bursts of intra MB’s for short periods • channel characteristics can be used as criteria ü cyclic intra refresh (CIR) • in error-free environment § multiple reference frame Video-Audio Processing

Resilience of Data Error Electrical Engineering National Central University Ø process § leaky prediction ü by attenuation of the energy of the prediction signal the energy of superimpose errors decays over time source Q F Q-1 F-1 0. 9 ME Video-Audio Processing

Resilience of Data Error Electrical Engineering National Central University Ø process § unrestricted motion vector (UMV) ü range of motion vectors and VLC table is different ü range of motion vectors depends on the picture size ü motion vectors are allowed to point outside the picture § advanced prediction (AP) ü overlapped block motion compensation (OBMC) ü four motion vectors per macroblock § motion compensation (MC) ü half-pel、quarter-pel ü using bilinear interpolation Video-Audio Processing

Summary Electrical Engineering National Central University Ø I have introduced § what’s data error § cause of data error § kind of data error § effect of data error § resilient of data error Ø by the introduction, we have basic realization on error Ø nothing is terrible but error Video-Audio Processing

Electrical Engineering National Central University Transcoding Ø Cascaded Pixel-Domain Transcoder (CPDT) § due to different reconstructed frames, drift is generated Q 1 -1 F F-1 Q 2 -1 MC F-1 MC/ME Video-Audio Processing

Electrical Engineering National Central University Transcoding Ø Simplified Pixel-Domain Transcoder (SPDT) § to reduce complexity of CPDT, by following simplification F-1 F-1 = F-1 F-1 Video-Audio Processing F =

Electrical Engineering National Central University Transcoding Ø Simplified Pixel-Domain Transcoder (SPDT) § under the following assumptions, SPDT is generated ü no clipping functions considered ü DCT and IDCT has infinite accurancy Q 1 -1 + - Q 2 -1 F MC F-1 Video-Audio Processing +