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Error Control Techniques for Interactive Low-bit Rate Video Transmission over the Internet.

Error Control Techniques for Interactive Low-bit Rate Video Transmission over the Internet. Injong Rhee Department of Computer Science North Carolina State University. Video Conferencing over Packet-Switching Networks. Packet Loss. ¡¡ Compressed video frame is packetized and transmitted.

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Error Control Techniques for Interactive Low-bit Rate Video Transmission over the Internet.

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  1. Error Control Techniques for Interactive Low-bit Rate Video Transmission over the Internet. Injong Rhee Department of Computer Science North Carolina State University

  2. 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.

  3. Motion Compensated Coding • Most video codecs use it. • Each P-frame depends on its previous frames. • I-frame is periodically transmitted. Temporal Dependency Inter Frame (P-frame) Intra Frame (I-frame)

  4. When a packet is lost,…. Packet Loss Inter Frame (P-frame) Intra Frame (I-frame) Error Propagation • Conventional Solution :Transmit I-framemore often. • However, compression efficiencyreduces.

  5. Myth: retransmission is not useful for interactive video TIME F0 F1 F2 F3 F1 (retransmit) retransmit lost (F1 arrives after its display) NACK F0 F1 F2 F3 Conventionally, late packets are discarded.

  6. Retransmission stops error propagation. TIME F0 F1 F2 F3 F1 (retransmit) retransmit lost F1 is recovered here NACK F0 F1 F2 F3 Don’t discard: Use late packets to recover their reference frames

  7. Handling retransmitted ‘late’ packets in decoder Inverse Quantization/DCT Current Frame Info Reference Frame Retransmitted Information. Current Diff.erence Frame Old Reference Frame + Display Motion Prediction Compensation

  8. Error Propagation

  9. Recovery from Error Propagation

  10. Error Recovery Technique • Recovery from Error Spread using Continuous Update(RESCU) • Focus on error spread/propagation • Continuous Update • Retransmission (this paper) • Forward error correction • Combined with Layer coding(this paper)

  11. Extending Packet Deadline • Add more frame buffers at the decoder. • Adjust Temporal Dependency Distance (TDD) of a frame. • TDD: frame intervals from that frame to its temporally dependent frame.

  12. Add more reference frame buffers.Cascaded Buffering • Minus: More computation and buffers at the decoder. • Plus :No change in the codec and picture pattern. Reference Frame 2 Reference Frame 1 Base Reference Frame Prediction Errors + MVs ContainsFull Image Prediction Errors + MVs

  13. Adjust Temporal Dependency DistancePeriodic TDDs (PTDD) • Changing Dependency. • f • PTDD can be dynamically adjusted. • Reduced Buffers & computations. • No protection fornon-periodicframe. Intra Inter Inter Periodic

  14. Continuous UpdatesRetransmission & Forward Error Correction • Retransmission • Retransmit lost packets within PTDD. • Retransmission delay requires larger PTDD. • Forward Error Correction • send parity packets over a PTDD period. Periodic frame Periodic frame Parity Packet for periodic frame

  15. Protecting non-periodic framesRESCU + Quality Assurance Layering • . • HPstream is sent with forward error correction. • RESCU contributes to reducing bit rates. HP HP HP HP LP LP LP LP

  16. protecting non-periodic frames Change temporal dependency • Errors in non-periodic frames do not propagate. • As PTDD increases, • Compression efficiency decreases. Periodic Inter Inter Periodic

  17. Compression Efficiency(MPEG-4 Class A, AKIYO) RESCU RESCU + QAL H.261 Intra-H261 AVG PSNR (dB) AVG Bytes/Frame

  18. Error Resilience (H.261 v.s. RESCU)

  19. RESCU + QAL

  20. Error Resiliencevarious loss groups RESCU + QAL Intra-H.261 PSNR RESCU H.261 Loss Rate

  21. Conclusions • RESCU accommodates delays in recovery (retransmission or FEC). • error resilience for interactivevideo. • high compression efficiency. • need I-frames less frequently. • Good for bandwidth-constrained, lossy networks (e.g., mobile wireless networks). • Much more work to be done.

  22. Error ResilienceRetransmission over various network delays 50 ms 100 ms 150 ms 200 ms 250 ms 300 ms

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