1 / 21

Retransmission-Based Error Control for Interactive Video Applications over the Internet

Retransmission-Based Error Control for Interactive Video Applications over the Internet. Injong Rhee ACM Multimedia ’98 Presented by: Jay A. Patel (some slides adapted from authors’ original presentation). Packet Loss. Video Conferencing over Internet.

garran
Download Presentation

Retransmission-Based Error Control for Interactive Video Applications over the Internet

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Retransmission-Based Error Control for Interactive Video Applications over the Internet Injong Rhee ACM Multimedia ’98 Presented by: Jay A. Patel (some slides adapted from authors’ original presentation)

  2. Packet Loss Video Conferencing over Internet • Compressed video frame is packetized and transmitted • Packet loss can occur quite frequently due to congestion

  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-frame more often • However, compression efficiencyreduces.

  5. Retransmission in Interactive Video? TIME F0 F1 F2 F3 F1 (retransmit) retransmit lost (F1 arrives after its display) NACK F0 F1 F2 F3 • Retransmission costs = 1.5 RTT (or 3 OWT) 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 Inverse Quantization/DCT Retransmitted Information Reference Frame Current Frame (Differences) + Display Motion Prediction Compensation

  8. Error Propagation

  9. Recovery from Error Propagation

  10. 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.

  11. More 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

  12. Extended Temporal Dependency Distance (ETDD) • Each frame depends on a frame in previous TDD • Retransmission errors delayed • Must maintain a base frame for each R-frame • Num of R-frames = value of TDD • Reduces compression • Prediction Error is computed from frames further away Each frame has TDD = 3

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

  14. Testing Methodology • H.261 encoder with PTDD = HP.261 • Compared with • H.261: base performance • INTRA-H261 • Good performance under packet loss errors • Intra-codes every block that changes significantly

  15. Video Stream • Trans-Atlantic Broadcast • 5 frames/sec, 352x288 resolution • 250 Kbits/sec • 40 sec, 190 frames, replayed for 5 minutes • Encoding method • Quantization step size 8 • 15x15 blocks w/ exhaustive search • TDD = 5 frames or 1 second

  16. Compression Efficiency

  17. Encoded Streams • Equalized Compression?

  18. Encoded Streams: Dissection

  19. Testing Methodology • Packetized using 512-byte packets • Only HP.261 is transmitted over the Internet • Trace collected from each experiment • Every hour for 8 days • ACK scheme • Receiver sends ACK for each frame received • Information on dropped packets • Retransmit restriction: 3 frames

  20. Testing Summary: Performance

  21. Conclusion • Retransmission can work for Interactive video • Requires minimal changes to the codecs • Advantage over INTRA-H.261 unclear

More Related