Compressed PTTVideo Traffic

8/13/2019 Compressed PTTVideo Traffic

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Lab-Experiment # 05

By

Eng. Naveed A. Umrani

Analyzing Compressed Video

Traffic


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Outlines

Purpose of the Lab

What is Digital Video

Advantage of Compression

MPEG Encoder Group-of-Picture (GOP)

VBR Video

Exercises Tasks

2 Principles of Teletraffic Engineering


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Purpose of the Lab

In this lab, you will explore theproperties of a traffic flowthat consists

of compressed digital video traffic.



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What is a Digital Video

Digital video consists of a sequence ofvideo frames that are displayed at a rate

of typically 30 frames per seconds.

Assuming a frame size of 720 x 480

pixels (a standard format used for digital

video) and a depth of 24bits per pixel,this results in a data rate 240Mbps per

video stream.



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Advantage of Compression

Using modern compression methods,such as MPEGand H.264, the data rate

can be drastically reduced to a few

Mbps.



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MPEG Encoder

An MPEG encoder (and most othercompression algorithms) generates

three types of frames:

Intra-coded (I), Inter-coded or predictive (P)

bi-directional (B)



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MPEG Encoder

Intra-Coded (I) Frames

I frames are coded as still images

Inter-coded or predictive (P)

P frames encode the differences from

the most recent I or P frame

bi-directional (B) B are interpolations of the next and

previous I or P frames.



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Group-of-Picture (GOP)

An MPEG encoder generates theseframes (I,P,B) in a repeating pattern,

called the Group-of-Picture (GOP)

pattern.

A typical GOP pattern of IBBPBBPBB,

where the dependencies betweenframes is indicated by arrows, is shown

in the following figure

8Principles of Teletraffic Engineering


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As indicated in the figure, frame types havedifferent sizes, with I frames being the largest

and B frames the smallest.

Note that a B frame is constructed from tworeference frames of type I or P (e.g., Frame 3

above depends on Frame 1 and Frame 4).

Thus, to encode or decode a B frame the

transmitter or receiver must have available thenext I or P frame.

To account for this need, frames are

transmitted in a different sequence than they

are displayed.10 Principles of Teletraffic Engineering


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In the above example, the display andtransmission sequence is as follows:

Display sequence: 1 2 3 4 5 6 7 8 9 10

Transmit sequence: 1 4 2 3 7 5 6 10 8 9



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Variable Bit Rate (VBR) Video

Due to the different sizes of I, P, and Bframes, the data rate of an MPEG

encoded video sources changes from

frame to frame. For this reason,compressed video such as MPEG, is

referred to a Variable Bit Rate (VBR)

video.



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Exercises Download a VBR video trace

Your first task is to download a file that contains a trace of a

VBR video source. The file contains the frame sizes

obtained from a compression of a picture movie. The size of

the file is 2.6 MB.

Content: Silence of the Lambs (~ 30 min)

Source Format: DVD

Frame size and rate: CIF 352x288 @30 fps

(frames per second)

Compression Algorithm: H.264/AVC (Full)

Quantizer (compression factor): 10

GoP Pattern: I B B B P B B P P B B B P B B B

Number of Frames: ~5400013 Principles of Teletraffic Engineering


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Exercises

Explore the content of the file. The file contains one line for each frame and has

multiple columns. The first four columns are

relevant for us:

Column 1: Sequence number of the frame (intransmit sequence)

Column 2: Display time of the frame

Column 3: Frame type

Column 4: Frame size in bytes

Columns 5 7: not used



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Exercises

[index, time, type_f, framesize_f, dummy1,dymmy2, dymmy3 ] = textread('movietrace.data',

'%f %f %c %f %f %f %f');

%Extracting the I,P,B frmes characteristics

from the source file

%frame size of I frames : framesize_I

%frame size of P frames : framesize_p

%frame size of B frames : framesize_B


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Exercisesa=0;b=0;

c=0;

for i=1:length(index)

if type_f(i)=='I'

a=a+1;

framesize_I(a)=framesize_f(i);

end

if type_f(i)=='B'

b=b+1;

framesize_B(b)=framesize_f(i);

endif type_f(i)=='P'

c=c+1;

framesize_P(c)=framesize_f(i);

end

end


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Exercises

Compute the following properties of thevideo trace. Number of frames and total number of bytes;

Size of the smallest frame, size of the largest frame, and

mean frame size;

Size of the smallest, largest and mean I, P, and B frame;

Mean bit rate (Computed as the mean frame size

divided by the frame duration);

Peak bit rate (Computed as the max. frame size dividedby the frame duration);

Ratio of the peak rate and the average rate. This peak-

to-average rate ratio is often used as an indicator how

bursty a traffic flow is. A flow with a peak-to-average ratio

of 10 or higher is highly variable.17 Principles of Teletraffic Engineering


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Exercises

%Hint1: You may use the MATLAB functions'length()','mean()','max()','min()'. which

calculate the length, mean, max, min of a

vector (for example max(framesize_P) will

give you the size of largest P frame.


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Exercises

Generate a set of graphs that show theproperties of the video trace:

1. Generate a graph that shows the frame

size as a function of the frame sequence

number. (Use the sequence in which the

frames are listed in the file, i.e., the transmit

sequence.)2. Generate a graph that shows the

distribution of I frames, P frames, and B

frames. (x-axis is the frame size, y-axis is

the relative frequency).


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Exercises

%Hint2: Use the 'plot' function to graphthe framesize as a function of the frame

sequence number.

%Hint3: Use the function 'hist' to show thedistribution of the frames. Before that

function type 'figure(2);' to indicate your

figure number.


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Exercises

Create three plots of the video traffic traceviewed at different scales. Each graph has

100 data points.

Plot 1: Generate a vector with 100 elements.

Starting with Frame 1, each element stores the

amount of data from 500 frames of the video

sequence.

1st element: #bytes from the first 500 frames

(frames 1, 2, , 500).

2nd element: #bytes from the frames 501,502, ,

1000.


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Exercises

initial_point=1;ag_frame=500;

jj=initial_point;

i=1;

bytes_f=zeros(1,100);

while i


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TasksPlot 2: Generate a vector with 100 elements. Starting with arandomly selected frame, each element stores the amount

of data from 50 frames of the video

sequence.

o Pick a random starting point, e.g., frame 3000.

o 1st element: #bytes from frames 3001, 3002, 3050.o 2nd element: #bytes from frames 3051, 3052, 3100.

o .

Plot 3: Generate a vector with 100 elements. Starting with arandomly selected frame, each element stores the amount

of data from 5 frames of the video sequence.o Pick a random starting point, e.g., frame 5010.

o 1st element: #bytes from frames 5010, 5011, 5015.

o 2nd element: #bytes from frames 5016, 5017, 5018.

o .

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