Guidelines for SelectingPractical MPEGGroup of Pictures: 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


Outline: Outline Introduction GOP Choices for Static MPEG GOP Choices for Streaming MPEG Conclusions


MPEG: 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)


GOP Choice: 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]


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. Video Quality Metrics


Outline: Outline Introduction GOP Choices for Static MPEG GOP Choices for Streaming MPEG Conclusions


Static GOP Tradeoffs: 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.


Static MPEG Methodology: 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 and NP on MPEG file size (MB) and frame quality measured by PSNR.


9 Video Clips: 9 Video Clips Each video is 300 raw images with CIF picture size (352x288) encoded at 30 fps. Quantization level is set at 3.


NBP Choice : NBP Choice Impact of NBP on Foreman Video


Slide11: High Motion Low Motion Medium Motion NBP Impact on Eight Videos


NP Choice: NP Choice Impact of NP on Foreman Video


NP Impact on Eight Videos : NP Impact on Eight Videos NBP = 2 High Motion Low Motion Medium Motion


Outline: Outline Introduction GOP Choices for Static MPEG GOP Choices for Streaming MPEG Conclusions


Streaming GOP Tradeoffs: 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


Streaming MPEG Methodology: 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.


Forward Error Correction (FEC): Forward Error Correction (FEC)


Pre-Encoding Temporal Scaling (PETS): Pre-Encoding Temporal Scaling (PETS) GOP rate Frame Size


Streaming MPEG Optimization Model: 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]


Streaming MPEG Performance Analysis: 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.


Streaming Foreman Video: Streaming Foreman Video 2 percent packet loss 1.5 Mbps capacity constraint


Eight Streaming MPEG Videos: Eight Streaming MPEG Videos 2 percent packet loss 1.5 Mbps capacity constraint Low Motion High Motion Medium Motion


Outline: Outline Introduction GOP Choices for Static MPEG GOP Choices for Streaming MPEG Conclusions


Conclusions: 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.


Guidelines for SelectingPractical MPEGGroup of Pictures: 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?