Retransmissionbased Error Control fr Interactive Video 基于重傳的交互式差錯控制

1、error control techniques for interactive low-bit error control techniques for interactive low-bit rate video transmission over the internet.rate video transmission over the internet.injong rheedepartment of computer sciencenorth carolina state universityvideo conferencing over packet-switching netwo

2、rks.video conferencing over packet-switching networks.packet loss compressed video frame is packetized and transmitted. packet loss can occur quite frequently due to congestion and user mobility. motion compensated codingmotion compensated codingintraframe(i-frame)interframe(p-frame)temporal depende

3、ncy most video codecs most video codecs use it.use it. each p-frame depends on its previous frameseach p-frame depends on its previous frames. i-frame is periodically transmittedi-frame is periodically transmitted.when a packet is lost,.when a packet is lost,.intraframe(i-frame)interframe(p-frame)pa

4、cket losserror propagation conventional solution : transmit i-frame more often. however, compression efficiency reduces.myth: retransmission is not useful for interactive videomyth: retransmission is not useful for interactive videoretransmitnacklostf0 f1 f2 f3 f1 (retransmit)f0 f1 f2 f3time(f1 arri

5、ves after its display)conventionally, late packets are discarded.retransmission stops error propagation.retransmission stops error propagation.retransmitnacklostf0 f1 f2 f3 f1 (retransmit)f0 f1 f2 f3timef1 is recovered heredont discarddont discard: use : use late packetslate packets to to recoverrec

6、over their their referencereference frames frameshandling retransmitted late packets in decoderhandling retransmitted late packets in decoderold reference framereferenceframecurrent diff.erenceframe+current frameinforetransmitted information.inverse quantization/dctmotion prediction compensationdisp

7、layerror propagationerror propagationrecovery from error propagationrecovery from error propagationerror recovery techniqueerror recovery techniquer recovery from ecovery from e error rror s spread using pread using c continuous ontinuous u updatepdate ( (rescurescu) )focus on error spread/propagati

8、onfocus on error spread/propagationcontinuous updatecontinuous update retransmission retransmission (this paper)(this paper) forward error correctionforward error correctioncombined with layer codingcombined with layer coding (this paper)(this paper)extending packet deadlineextending packet deadline

9、1add more frame buffersadd more frame buffers at the decoder. at the decoder.2adjust temporal dependency distanceadjust temporal dependency distance (tdd) of a frame. (tdd) of a frame. tdd: frame intervalstdd: frame intervals from that frame to its temporally dependent from that frame to its tempora

10、lly dependent frame.frame.add more reference frame buffers.add more reference frame buffers.cascaded bufferingcascaded bufferingminus: more computation and buffers at the decoder.plus : no change in the codec and picture pattern.base reference framereference frame 1contains full imageprediction erro

11、rs + mvsprediction errors + mvsreference frame 2adjust temporal dependency distanceadjust temporal dependency distance periodic tdds (ptdd)periodic tdds (ptdd)changing dependency.f f ptdd can be dynamically adjusted ptdd can be dynamically adjusted.+reduced buffers & computationsreduced buffers

12、& computations.no protection no protection forfor non-periodicnon-periodic frame.frame.intra inter inter periodiccontinuous updatescontinuous updatesretransmission & forward error correctionretransmission & forward error correctionretransmission retransmit lost packets within ptdd.retran

13、smission delay requires larger ptdd.forward error correctionsend parity packets over a ptdd period.periodic frameperiodic frameparity packet for periodic frameprotecting non-periodic framesprotecting non-periodic frames rescu + quality assurance layeringrescu + quality assurance layering .hphp strea

14、m is sent with stream is sent with forward error correction. forward error correction. rescurescu contributes to contributes to reducing bit rates.reducing bit rates.hplphplphplphplpprotecting non-periodic frames protecting non-periodic frames change temporal dependencychange temporal dependencyerro

15、rserrors in non-periodic frames in non-periodic frames do not propagate.do not propagate.as ptdd increases,as ptdd increases, compression efficiency decreases.compression efficiency decreases.periodic inter inter periodiccompression efficiencycompression efficiency(mpeg-4 class a, akiyo)(mpeg-4 clas

16、s a, akiyo)avg bytes/frameavg psnr (db)intra-h261rescu + qalrescuh.261error resilienceerror resilience (h.261 v.s. rescu) (h.261 v.s. rescu)rescu + qalrescu + qalerror resilienceerror resiliencevarious loss groupsvarious loss groupsh.261intra-h.261loss ratepsnrrescu + qalrescuconclusionsconclusionsr

17、escu accommodates delays in recovery (retransmission or rescu accommodates delays in recovery (retransmission or fec).fec).error resilience for interactiveerror resilience for interactive video.video.highhigh compression efficiency. compression efficiency. need i-frames less frequently.need i-frames less frequently.good for good for bandwidth-constrained, lossybandwidth-constrained, lossy networks (e.g.,