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

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Outline

• Introduction
• GOP Choices for Static MPEG
• GOP Choices for Streaming MPEG
• Conclusions

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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)

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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
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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.

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Outline

• Introduction
• GOP Choices for Static MPEG
• GOP Choices for Streaming MPEG
• Conclusions

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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.

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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.

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9 Video Clips

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

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NBP Choice
Impact of NBP on Foreman Video
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NBP Impact on Eight Videos
High Motion
Medium Motion
Low Motion
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NP Choice
Impact of NP on Foreman Video
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NP Impact on Eight Videos
High Motion
Medium Motion
Low Motion

• NBP 2

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Outline

• Introduction
• GOP Choices for Static MPEG
• GOP Choices for Streaming MPEG
• Conclusions

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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

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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.

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Forward Error Correction (FEC)
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Pre-Encoding Temporal Scaling (PETS)

• GOP rate
• Frame Size

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Streaming MPEG Optimization Model
WCK03

• 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

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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.

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Streaming Foreman Video

• 2 percent packet loss
• 1.5 Mbps capacity constraint

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Eight Streaming MPEG Videos
Low Motion
Medium Motion
High Motion

• 2 percent packet loss
• 1.5 Mbps capacity constraint

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Outline

• Introduction
• GOP Choices for Static MPEG
• GOP Choices for Streaming MPEG
• Conclusions

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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.

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