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

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

3. Euro IMSA February 14, 2006 3 MPEG Group Of Pictures (GOP) –IBBPBBPBBPBB IBBPBBPBBPBBI… Important Definitions –N P : number of P frames in one GOP –N BP : number of B frames between two reference frames (I or P frame)

4. 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]

5. Euro IMSA February 14, 2006 5 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. Video Quality Metrics

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

7. 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.

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

9. 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.

10. Euro IMSA February 14, 2006 10 N BP Choice Impact of N BP on Foreman Video

11. Euro IMSA February 14, 2006 11 High Motion Low Motion Medium Motion N BP Impact on Eight Videos

12. Euro IMSA February 14, 2006 12 N P Choice Impact of N P on Foreman Video

13. Euro IMSA February 14, 2006 13 N P Impact on Eight Videos N BP = 2 High Motion Low Motion Medium Motion

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

15. 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

16. 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 N BP and N P. Study the impact of N BP and N P on streaming performance.

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

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

19. Euro IMSA February 14, 2006 19 Streaming MPEG Optimization Model where: R is playable frame rate S I, S P and S B are the frame sizes S IF, S PF and S BF are the FEC frame sizes N P and N B are the number of P and B frames G is the GOP rate T is the capacity constraint [WCK03]

20. 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 N BP and N P.

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

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

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

24. 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.

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