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P2P Digital TV Recorder

Supervisor: Professor Michael R. Lyu

Prepared by: Ho Tsz Wing, AndyLau Wai Shun, Jack

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Content

1. Project background and objectives2. Summary of Work in Semester 13. Improvements in Semester 2

a) Decentralized searching algorithm and buddy list

b) Decentralized recording algorithm and bonus system

c) Streaming and video format conversion

4. Difficulties and Solution5. Further Improvements6. Conclusion

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Project backgroundWatching TV is a major entertainmentPeople often miss their favorite

programsPeople need to schedule the

recording of the programs

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Project objectivesAllow people to view back a previous

TV program without doing scheduling themselves

Let the users view the program on demand

Increase the availability of the TV programs

Achieve load balancing among the participating peers

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Summary of Work in Sem1

Program CoreProgram Core1. Download the video file from

other peers2. No Buddy List3. All peers’ information is stored in

a centralized server4. A centralized scheduling

algorithm5. Peers unable to reject the

recording task6. Using a complex algorithm to

achieve high availability

P2P Digital TV RecorderP2P Digital TV Recorder

Performance enhancementPerformance enhancement 1. Whole file replication2. Erasure code replication

Research ResultsResearch Results1. In most cases, erasure code

replication performs better than whole file replication

2. When the peer availability attains a certain level, the performance of the whole file replication close to erasure code replication

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Improvement Work in Sem2

Problem

Performance of the server become the bottleneck of the system

Cause

Queries needed to handle increase dramatically with the increase of the number of peers

Solution

Use buddy list system

Try to keep as less as information in the sever

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Improvement Work in Sem2

Problem

Peers cannot reject the recording tasks => Inflexible

Cause

A centralized server will assign the recording task to the online peer without considering their contribution to the system

Solution

A distributed scheduling algorithm

Implement a bonus system

The user is able to accept or reject the task

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Improvement Work in Sem2

Problem

Replication methods take too much time and CPU resource

Cause

As the original video in dvr-ms format is too large, no matter which replication we use, much time is consumed.

Solution

Implement a streaming server

Real time encoding is fast enough

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Improvement Work - 1

1. Decentralized searching algorithm and buddy list2. Decentralized recording algorithm and bonus system

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User Search Application

Login/Logout Application

Xml.asp

Database

Component of Server

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Login / Logout / User Search

DirectoryDirectoryServerServer

BB

EE

CC

DD

AAOnline

Offline

Offline

Online Online

Online

Login message

Buddy Information

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Task of Client Side

Client Application

Download

Streaming Recording

Download (Implemented)

• Basic function • Send the video file to the

requested peer

Streaming

• Encoding to wmv• Preview function

Recording

• Scheduling among

peers• Bonus system

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Download Topology – Napster (Sem1)

Owner@

Client

Lookup(“TVB News”)

N6

N9 N7

Server

N8

N3

N2N1

Simple, but O(N) states and a single point of failure

Key=“TVB News”

N4

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Download Topology – Gnutella (Sem 2)

N4Owner@

Client

N6

N9

N7N8

N3

N2N1

Robust, but in the worst case O(N) messages per lookup

Key=“TVB News”

Lookup(“TVB News”)

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P2P Digital TV Recorder Protocol

Download & Streaming / Recording MessageIP

IDType

Program TitleTTL / Hop

Port / Channel

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Performance Enhancement

Forward the message to other peersForward the message to other peersForward the message to other peersForward the message to other peers

All pass

CheckCheckIPIP

FieldField

Check Check Message Message

IDID

Check Check TTLTTL

Check Check File File

ExistExist

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Scheduling of Recording Task

1. Peers initialize the recording task when the program starts

2. Peers are able to determine recording or not if the bonus points of the peers attain a particular level

3. Peers forward the recording message to one of its buddies

1. Server will schedule the recording of all program in the morning

2. Send out the recording request to 2 peers randomly before the program starts

3. Peers who received the recording request cannot reject it.

Centralized Decentralized

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Scheduling PoliciesIncoming message

Check IP Field

Check Message ID

Unequal

Forward the Recording message

Equal

Check Points

Check Hops

First Time

Repeated

Equal

Unequal

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Scheduling Policies

Check Points

Forward the Recording message

Recording the Program

Record Or Not ?

Above 10

Below 10

NoPoint

DecrementYes

PointIncrement

PointIncrement

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Bonus System

Free Rider

unable to decide record or not

Normal User

able to decide record or not

10 10+

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Improvement Work - 2

Video-On-Demand (VoD) streaming

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Why use VoD streaming?

Download the user needs to wait for a long time errors may occur in the downloading process

VoD streaming save the user a lot of time and storage space can be used as a preview function

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Windows Media Encoder SDK

DirectShow Library

GraphEdit

Tools used in developing the streaming application

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DirectShow Library

a media-streaming architecture for the Microsoft Windows® platform

provides for high-quality capture and playback of multimedia streams

Example uses: file players video editing applications file format converters etc.

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DirectShow Filters and Filter Graphs

DirectShow Filters receive multimedia streams as input and produce

output A source filter introduces data into the graph. A transform filter takes an input stream, processes

the data, and creates an output stream. Renderer filters receive data and present it to the user

Filter Graphs A set of connected filters controlled by a high-level component called the Filter

Graph Manager

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DirectShow Architecture

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Writing a DirectShow Application

The application1. creates an instance of the Filter Graph Manager.

2. uses the Filter Graph Manager to build a filter graph.

3. uses the Filter Graph Manager to control the filter graph and stream data through the filters.

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Approaches in Graph Building

Approach Method Used

The Filter Graph Manager builds the entire graph

RenderFile

The Filter Graph Manager builds part of the graph

Render

The application builds the entire graph AddFilter, Connect or ConnectDirect

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Reasons for using DirectShow Library

1. Windows MCE records TV programs in dvr-ms format

2. Dvr-ms files are not efficient for storage (1hr TV program recorded in good quality requires about 1668MB)

3. Dvr-ms files cannot be streamed over the internet

4. DirectShow is used to convert dvr-ms file to wmv file that can be used for streaming

5. The file size of 1 hr wmv file is only 101MB if the bit rate is 225kbps

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Number of days of TV programmes that can be recorded with a given hard disk size

20.63

1.250

5

10

15

20

25

0 20 40 60

Harddisk size (GB)

Num

ber

of d

ays

Harddisk size dvr-ms wmv

1.31

22.09

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GraphEditThe filter graph built by our

application

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Uses of DirectShow Library

Steps to convert dvr-ms file to wmv file using DirectShow Library:1. start once Windows MCE has finished recording a

particular TV program

2. create the filter graph and render the dvr-ms file

3. original dvr-ms file will be deleted in the case that the storage space is not sufficient for new recording

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Experiment Result

Bit Rate (Kbps)

Video Size File Size (KB)

Conversion Time (s)

218 320 x 240 1,711 58

441 320 x 240 3,317 60

666 320 x 240 4,928 62

218 480 x 360 1,731 115

441 480 x 360 3,413 116

666 480 x 360 5,069 125

The dvr-ms file used in this experiment has a length of 60s, a file size of 27,399KB and is recorded in good quality

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Experiment Result

Bit Rate (Kbps)

Video Size File Size (KB)

Conversion Time (s)

666 320 x 240 4,928 62

666 480 x 360 5,069 125

666 640 x 480 5,170 209

666 800 x 600 5,194 327

The dvr-ms file used in this experiment has a length of 60s, a file size of 27,399KB and is recorded in good quality

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Windows Media Encoder SDK

used to compress live or stored audio and video content into Windows Media files or streams

create multimedia productions from devices attached to their computers

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Steps to create an encoding application

Create Encoder Object

Create/Load Profile Object Associate

Profile with Encoder

Add Source in Source Group Collection in

Encoder Object

Provide Audio Or Video Input source (e.g. File, Device

Name)

Add Source type (Audio or Video or

Both) in source Group

Provide Encoder output (e.g. File,

Broadcast)

Start the encoding session

General Encoder Flow

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Encoding with CBR and VBR

Constant Bit Rate (CBR) Encoding bit rate and size of the content are known before

encoding for content that varies in complexity, the encoding

quality is not constant

Variable Bit Rate (VBR) Encoding it compensates for changes in the complexity of the

content bit rate and size of the content are not known before

the encoding

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Uses of Windows Media Encoder SDK

1. When the client receives a streaming request, it will create an encoder object, encode the appropriate file using CBR encoding and broadcast it at the address http://localhost:8080

2. It then connects to the requesting peer and the peer will view the file at the specified address

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Streaming Architecture

DirectoryDirectoryServerServer

BB

EE

CC

DD

AAStreaming Host

Streaming Host

Streaming Host

Streaming Host

Streaming Host

Streaming request

Streaming request

Connection established

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Difficulties and Solutions

Difficulty Dvr-ms file (the default file format for the recorded TV

in Windows MCE) cannot be streamed over the Internet

Cause Windows Media Encoder 9 Series SDK does not

support the encoding and broadcasting of dvr-ms file

Solution We have to use DirectShow Library to convert the

dvr-ms file to a format that is compatible with Windows Media Encoder 9 Series SDK (i.e. wmv file).

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Difficulties and Solutions

Difficulty The wmv file resulted from the conversion of dvr-ms

file by DirectShow Library has sound only but no video.

Cause The default transform filter chosen by the RenderFile

method (InterVideo Video Decoder) cannot decode MPEG-2 stream to MPEG-1 stream

Solution So we have chosen to use the GPL MPEG-1/2

Decoder in our filter graph to solve this problem

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Further improvement

It is possible to have real time streaming in the following ways: First, we can start the file conversion as soon as

Windows MCE starts to record the TV program Next, we can use Windows Media Encoder SDK to

encode the wmv file and broadcast it at http://localhost:8080

Finally, the client can connect to the above address to get the video content instantly

However, there is one drawback as doing recording and converting at the same time takes up a lot of CPU time

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Further improvementIt is also possible to use p2p

technique to stream the file It can reduce the network bottleneck at the video

server It can provide a fault tolerant Video-on-Demand

streaming it raises technical, performance, quality, business,

and legal issues

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Conclusion

We have implemented our application in a decentralized ways using a buddy list system to enhance the performance.

We have introduced a distributed scheduling algorithm and a bonus system to enhance the availability of the TV programmes.

We have also developed a streaming server to reduce the storage requirement and enabled the user to preview the TV programmes.

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