Technion Israel Institute of Technology Faculty of Electrical Engineering CCITComputer Network Labor

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Technion- Israel Institute of Technology Faculty
of Electrical EngineeringCCIT-Computer Network
Laboratory

• The Influence of Packet Loss On Video Quality
• By Revital and Merav Huber.
• Supervisor Dr. Ofer Hadar.
• Winter 1998/9

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Network Simulation
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Target

• Finding the connection between communication
  network performance and the quality of a
  compressed video signal.
• Destination determination of the packet loss
  model which causes the smallest degradation of
  the received movie.

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Loss Models of The Network
IID
Burst
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Assumption

• Bursts of information loss would be less noticed
  than other error forms.
• reasons
• Error in a number of pixels on consequent frames,
  is noticed by viewer more than a frame loss,
  because of movie speed.
• When bursts occur, following packets are
  degraded, which belong to the same frame.

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Theoretical Background

• MPEG
• Motion Picture Experts Group
• Video audio signals synchronization.
• Video transfer by frames.
• Frame types are determined by encoding
• Intracoded encoded by JPEG.
• Predictive use of block- differences between
  the previous frame and the present frame.
• Bidirectional use of block- differences between
  the encoded frame the previous the next
  frames.

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Theoretical Background, MPEG
I frame
Bframe
B frame
Pframe
B frame
B frame
Pframe
B frame
B frame
Pframe
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MPEG Movies
Cirinout.mpg
cirinout
Received.mpg
received
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Theoretical Background- Quality Factors

• Delay
• Quantization of MPEG encoding
• Lossy network
• causes
• errors due to broadcast bursts.
• Routing errors.
• When buffers are finite and there is overflow, it
  is possible packets loss will occur.

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Performance Idea

• A lossy network simulation, transmitting a video
  signal.
• The video signal is divided into packets.
• The receivers information is the arriving
  packets.
• Comparison between the transmitted and received
  signals, by PSNR.
• Measuring edge sharpness by MTF.
• Measuring power spectrum.

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Tested Video Signal
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Quality Measurements
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MTF
Ideal edge
Smeared Edge
1. Image
2. Gray Level
x
x
3. LSF
x
x
4. MTF
1
1
False response
f
f
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Results - Example
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Results - PSNR
Pe0.02
Burst
IID
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Results - MTF
Pe0.01
Burst
IID
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Results - Power Spectrum
Pe0.02
Burst
IID
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Conclusions

• Burst loss model effects less frames of the movie
  than IID.
• Problems
• MATLAB created 2D frames, instead of 3D.
• Cut -off video signals during decoding.
• Adding lost pictures and erasing created ones
  distorted some of the results.
• Though the used quality measurements arent
  ideal, they agree with the theory, and
  represented well the quality a human eye would
  notice.

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Summary - PSNR

• PSNR isnt the ideal measurement of the received
  movie quality. Reasons
• Each frame is analyzed separately, with no
  consideration of time sequence. A measurement for
  video quality should consider time sequence.
• The PSNR result doesnt determine the picture
  quality, because it uses a comparison, instead of
  an absolute value.

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Summary - MTF

• The distortion of the signals isnt linear, thus
  MTF doesnt represent only the smearing of the
  edge response.
• Legal frame MTF(f0)1. Other values represent
  other forms of degradation.
• Number of legal frames is a very small portion of
  the total number of frames in the movie.

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Summary- Power Spectrum

• Conclusion is achieved by comparing results of
  several simulations on a vector, with different
  parameters.

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The End