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An Analytic Comparison of RPS Video Repair

An Analytic Comparison of RPS Video Repair. Yubing Wang , Mark Claypool , Robert Kinicki Computer Science Department WPI Worcester, Massachusetts, USA. ACM/SPIE Multimedia Computing and Networking (MMCN) San Jose, California, January 31, 2008. Introduction.

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An Analytic Comparison of RPS Video Repair

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  1. An Analytic Comparison of RPS Video Repair Yubing Wang, Mark Claypool,Robert Kinicki Computer Science Department WPI Worcester, Massachusetts, USA ACM/SPIE Multimedia Computing and Networking (MMCN) San Jose, California, January 31, 2008

  2. Introduction • Packet loss degrades video quality • Reference Picture Selection (RPS) selects one of several previous frames as a reference frame • Stops error propagation more quickly than ARQ • Consume less network capacity than FEC and ARQ • Two modes: NACK (optimistic) and ACK (pessimistic) But … effectiveness and choice depends on packet loss, round-trip time, video content and GOP size • This work  analyze video quality with RPS • Two analytical models, RPS NACK and RPS ACK • Analysis of loss rate, round-trip time, video content, GOP Determine choice between NACK and ACK

  3. Outline • Introduction (done) • Background (next) • Analytical Models • Analysis • Conclusions

  4. Reference Picture Selection - ACK • Decoder acknowledges all correctly received frames • Only acknowledged frames used as reference • Error propagation avoided entirely • Reference distance increases with round-trip time • Coding efficiency decreases with reference distance • Video quality degrades due to limited bit-rate 6 7 1 3 4 5 2 ACK(1) ACK(2) ACK(3)

  5. Reference Picture Selection - NACK • Previous frame used as reference during error-free transmission • Reference distance always 1 regardless of round-trip time • Better coding efficiency • Decoder sends NACK for erroneous frame and reference frame number • Suffers from error propagation • Loss propagation increases with round-trip time 5 6 7 8 1 3 4 2 NACK(3)

  6. Outline • Introduction (done) • Background (done) • Analytical Models (next) • Analysis • Conclusions

  7. Parameters for Analytic Models

  8. Summary of Analytical Models Average Quality for RPS ACK: Average Quality for RPS NACK:

  9. Outline • Introduction (done) • Background (done) • Analytical Models (done) • Analysis (next) • Conclusions

  10. Quality versus Round-Trip Time RPS NACK RPS ACK • Quality degrades with round-trip time increase • NACK resistant to degradation with round-trip time for low loss • ACK degrades uniformly with round-trip time

  11. Quality versus Loss Rate RPS NACK RPS ACK • Quality degrades with loss rate increase • NACK degrades faster with high round trip times • ACK uniform degradation

  12. Loss Crossover versus Round-Trip Time • Above trend line, ACK better. Below trend line, NACK better • Crossover points for low-motion are higher than for high-motion • Error propagation more harmful to quality than reference distance

  13. Quality versus GOP Length RPS NACK RPS ACK • With RPS, quality increases with GOP length • NACK performs no worse than no repair • For small GOP, RPS ACK worse than no repair

  14. Conclusions • RPS ACK outperforms RPS NACK when round-trip times are low • RPS NACKoutperforms RPS ACK when the loss rate is low • RPS NACK outperforms RPS ACK over a wider range for low motion videos than for high motion videos • RPS NACK always performs the same or better than no repair, but RPS ACK can perform worse than no repair for small GOP sizes

  15. Future Work • Use Video Quality Metric (VQM) to analyze RPS performance • Explore the impact of network capacity constraints on RPS performance

  16. An Analytic Comparison of RPS Video Repair Yubing Wang, Mark Claypool,Robert Kinicki Computer Science Department WPI Worcester, Massachusetts, USA ACM/SPIE Multimedia Computing and Networking (MMCN) San Jose, California, January 31, 2008

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