Technion- Israel Institute of Technology Faculty of Electrical Engineering

CCIT-Computer Network Laboratory

The Influence of Packet Loss On Video Quality

By: Revital and Merav Huber.Supervisor: Dr. Ofer Hadar.

Winter 1998/9

Network Simulation

Analog video Encoder Transmitter

Noisy communication

network

Receiver Decoder Analog video

Original movie Received movie

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.

Loss Models of The Network

lost. is packet single

passes. packet

]1,0[

PeR

PeR

R

[1,10] burst of size :D

lost, is packet)loss massage(

passes. packet)loss massage(

size). burst average/()loss massage(

raw

R<P

PR

PeP

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.

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.

Theoretical Background, MPEG

I frame

Bframe B

frameP

frameB

frameB

frameP

frameB

frameB

frameP

frame

MPEG Movies

Cirinout.mpg

Received.mpg

Cirinout.mpg

Received.mpg

cirinout

received

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.

Performance Idea

• A lossy network simulation, transmitting a video signal.

• The video signal is divided into packets.• The receiver’s information is the arriving packets. • Comparison between the transmitted and received

signals, by PSNR. • Measuring edge sharpness by MTF.• Measuring power spectrum.

Tested Video Signal

Quality Measurements

eM N

sent n m received n m

PSNRP

e

MSE

m

M

n

N

MSE

1

10

2

11

10

2

** [ ( , ) ( , )]

log ( )

(x)

onse(x))(edge_respFFTMTF(f)

xx

j j

j j n

n

S e eX

X e x n e

( ) ( )

( ) [ ]

2

MTF

4. MTF

3. LSF

1. Image

2. Gray Level

1

x x

x x

f f

1

Ideal edge Smeared Edge

False response

Results - Example

Results - PSNR

Pe=0.02Burst IID

Results - MTF

Pe=0.01Burst IID

Results - Power Spectrum

Burst IIDPe=0.02

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 aren’t ideal, they agree with the theory, and represented well the quality a human eye would notice.

Summary - PSNR

• PSNR isn’t 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 doesn’t determine the picture quality, because it uses a comparison, instead of an absolute value.

Summary - MTF

• The distortion of the signals isn’t linear, thus MTF doesn’t represent only the smearing of the edge response.

• Legal frame: MTF(f=0)=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.

Summary- Power Spectrum

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

The End