Guidelines for Selecting Practical MPEG Group of Pictures

1. Guidelines for SelectingPractical MPEGGroup of Pictures Huahui Wu, Mark Claypool and Robert Kinicki Worcester Polytechnic Institute Computer Science Department Worcester, MA, 01609 USA Presenter - Bob Kinicki The IASTED International Conference onInternet and Multimedia Systems and Applications (EuroIMSA 2006)February 13-15, 2006 Innsbruck, Austria

2. Outline • Introduction • GOP Choices for Static MPEG • GOP Choices for Streaming MPEG • Conclusions Euro IMSA February 14, 2006

3. MPEG • Group Of Pictures (GOP) • IBBPBBPBBPBBIBBPBBPBBPBBI… • Important Definitions • NP: number of P frames in one GOP • NBP : number of B frames between two reference frames (I or P frame) Euro IMSA February 14, 2006

4. GOP Choice • GOP choice determines MPEG properties • Frame size, picture quality • Streaming data rate, perceived quality • Our exhaustive search approach needs practical limits for the GOP length. • Current GOP choice is mostly intuitive! • 300 frames long by default in VirtualDub • 10 seconds long in NOSSDAV 2005 online video. • Mayer-Patel [6] searches a large GOP range (i.e, 35 P frames). [MLC02] Euro IMSA February 14, 2006

5. Video Quality Metrics • Playable Frame Rate • Counting frames • Temporal domain • Appropriate when every frame does not change its content. • Peak Signal to Noise Ratio (PSNR) • Counting pixel differences for each frame • Quality domain • Appropriate when there is no frame loss. • VQM • Temporal + Quality domain • Handles temporal loss and quality distortion. Euro IMSA February 14, 2006

6. Outline • Introduction • GOP Choices for Static MPEG • GOP Choices for Streaming MPEG • Conclusions Euro IMSA February 14, 2006

7. Static GOP Tradeoffs • More B frames • Advantage: smallest frame size reduces the average frame size • Disadvantage: decreases inter-frame similarity, increase B frame size • More P frames • Advantages: smaller than I frame, reduces the average frame size • However, supporting VCR functions is better with short GOPs. Euro IMSA February 14, 2006

8. Static MPEG Methodology • Use the Berkeley MPEG encoder and decoder. • Choose varying combinations of NBP and NP. • Encode raw images into video clips. • Study the impact of NBP andNP on MPEG file size (MB) and frame quality measured by PSNR. Euro IMSA February 14, 2006

9. 9 Video Clips • Each video is 300 raw images with CIF picture size (352x288) encoded at 30 fps. • Quantization level is set at 3. Euro IMSA February 14, 2006

10. NBP Choice Impact of NBP on ForemanVideo Euro IMSA February 14, 2006

11. NBP Impact on Eight Videos HighMotion MediumMotion LowMotion Euro IMSA February 14, 2006

12. NP Choice Impact of NP on ForemanVideo Euro IMSA February 14, 2006

13. NP Impact on Eight Videos NBP = 2 High Motion Medium Motion Low Motion Euro IMSA February 14, 2006

14. Outline • Introduction • GOP Choices for Static MPEG • GOP Choices for Streaming MPEG • Conclusions Euro IMSA February 14, 2006

15. Streaming GOP Tradeoffs • More B frames • Advantages • Low data rate • Easy to get through a lossy network • Disadvantages: • Low inter-frame similarity • Add decoding latency • More P frames • Advantage • low data rate • Disadvantages • Increases propagation errors • Repair techniques need to be used Euro IMSA February 14, 2006

16. Streaming MPEG Methodology • Develop a streaming MPEG model with packet loss and a capacity constraint • Forward Error Correction (FEC) • Pre-Encoding Temporal Scaling (PETS) • Estimate the video quality (measured by playable frame rate). [WCK03 • Choose varying combinations of NBP and NP. • Study the impact of NBP and NP on streaming performance. Euro IMSA February 14, 2006

17. Forward Error Correction (FEC) Euro IMSA February 14, 2006

18. Pre-Encoding Temporal Scaling (PETS) • GOP rate • Frame Size Euro IMSA February 14, 2006

19. Streaming MPEG Optimization Model where: R is playable frame rate SI, SP and SB are the frame sizes SIF, SPF and SBF are the FEC frame sizes NP and NB are the number of P and B frames G is the GOP rate T is the capacity constraint [WCK03] Euro IMSA February 14, 2006

20. Streaming MPEG Performance Analysis • Three FEC choices • Non-FEC • 5% Fixed FEC • Adjusted FEC via the optimization model • Use PETS to respond to the capacity constraint. • Study varying combinations of NBP and NP. Euro IMSA February 14, 2006

21. Streaming Foreman Video 2 percent packet loss 1.5 Mbps capacity constraint Euro IMSA February 14, 2006

22. Eight Streaming MPEG Videos 2 percent packet loss 1.5 Mbps capacity constraint Low Motion Medium Motion High Motion Euro IMSA February 14, 2006

23. Outline • Introduction • GOP Choices for Static MPEG • GOP Choices for Streaming MPEG • Conclusions Euro IMSA February 14, 2006

24. Conclusions • For Static MPEG Videos • The number of B frames between two references frames should not exceed 2. • The number of P frames in a GOP need not be more than 5. • For Streaming MPEG Videos • The number of B frames between two reference frames should be kept at 2 except when dealing with a delay constraint. • The number of P frames in a GOP need not be more than 5. Euro IMSA February 14, 2006

25. Thank You!Questions? Guidelines for SelectingPractical MPEGGroup of Pictures Huahui Wu, Mark Claypool and Robert Kinicki Worcester Polytechnic Institute Computer Science Department Worcester, MA, 01609 USA