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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 Presenter - Bob Kinicki

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Guidelines for Selecting Practical MPEG Group of Pictures

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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


Outline

  • Introduction

  • GOP Choices for Static MPEG

  • GOP Choices for Streaming MPEG

  • Conclusions

Euro IMSA February 14, 2006


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


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


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


Outline

  • Introduction

  • GOP Choices for Static MPEG

  • GOP Choices for Streaming MPEG

  • Conclusions

Euro IMSA February 14, 2006


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


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 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


NBP Choice

Impact of NBP on ForemanVideo

Euro IMSA February 14, 2006


NBP Impact on Eight Videos

HighMotion

MediumMotion

LowMotion

Euro IMSA February 14, 2006


NP Choice

Impact of NP on ForemanVideo

Euro IMSA February 14, 2006


NP Impact on Eight Videos

NBP = 2

High Motion

Medium Motion

Low Motion

Euro IMSA February 14, 2006


Outline

  • Introduction

  • GOP Choices for Static MPEG

  • GOP Choices for Streaming MPEG

  • Conclusions

Euro IMSA February 14, 2006


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


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


Forward Error Correction (FEC)

Euro IMSA February 14, 2006


Pre-Encoding Temporal Scaling (PETS)

  • GOP rate

  • Frame Size

Euro IMSA February 14, 2006


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


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


Streaming Foreman Video

2 percent packet loss

1.5 Mbps capacity constraint

Euro IMSA February 14, 2006


Eight Streaming MPEG Videos

2 percent packet loss

1.5 Mbps capacity constraint

Low Motion

Medium Motion

High Motion

Euro IMSA February 14, 2006


Outline

  • Introduction

  • GOP Choices for Static MPEG

  • GOP Choices for Streaming MPEG

  • Conclusions

Euro IMSA February 14, 2006


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


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


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