An Analytic Comparison of RPS Video Repair

ACM/SPIE Multimedia Computing and Networking (MMCN)

San Jose, California, January 31, 2008

Yubing Wang, Mark Claypool, Robert Kinicki

Computer Science DepartmentWPI

Worcester, Massachusetts, USA

2MMCN 08, Jan. 31, 2008

IntroductionIntroduction

Packet loss degrades video qualityReference 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 ARQTwo 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 RPSTwo analytical models, RPS NACK and RPS ACKAnalysis of loss rate, round-trip time, video content, GOP

Determine choice between NACK and ACK

3MMCN 08, Jan. 31, 2008

OutlineOutline

Introduction(done)Background (next)Analytical ModelsAnalysisConclusions

4MMCN 08, Jan. 31, 2008

Reference Picture Selection - ACKReference 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

1 2 3 4 5 6 7

ACK(1) ACK(2) ACK(3)

5MMCN 08, Jan. 31, 2008

Reference Picture Selection - NACKReference 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

NACK(3)

1 2 3 4 5 6 7 8

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OutlineOutline

Introduction(done)Background (done)Analytical Models(next)AnalysisConclusions

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Parameters for Analytic ModelsParameters for Analytic Models

8MMCN 08, Jan. 31, 2008

Summary of Analytical ModelsSummary of Analytical ModelsAverage Quality for RPS ACK:

Average Quality for RPS NACK:

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9MMCN 08, Jan. 31, 2008

OutlineOutline

Introduction(done)Background (done)Analytical Models(done)Analysis(next)Conclusions

10MMCN 08, Jan. 31, 2008

Quality versus Round-Trip TimeQuality 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

11MMCN 08, Jan. 31, 2008

Quality versus Loss RateQuality versus Loss Rate

RPS NACK RPS ACK Quality degrades with loss rate increase

NACK degrades faster with high round trip times

ACK uniform degradation

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Loss Crossover versus Round-Trip

Time 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

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13MMCN 08, Jan. 31, 2008

Quality versus GOP LengthQuality 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

14MMCN 08, Jan. 31, 2008

ConclusionsConclusions

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

15MMCN 08, Jan. 31, 2008

Future WorkFuture Work

Use Video Quality Metric (VQM) to analyze RPS performance

Explore the impact of network capacity constraints on RPS performance

An Analytic Comparison of RPS Video Repair

ACM/SPIE Multimedia Computing and Networking (MMCN)

San Jose, California, January 31, 2008

Yubing Wang, Mark Claypool, Robert Kinicki

Computer Science DepartmentWPI

Worcester, Massachusetts, USA