Digital Television via IP Multicast

Digital Television via IP Multicast

Group 15M

Lee Howes (Group Leader)James Robinson (Group Secretary)

Ashley BrownJay Cornwall

Simon FothergillLyndon Leggate

Project Summary

• Allow networked PCs in the Department of Computing to receive and display television programmes.

• Take Television channels from a Digital Terrestrial Television (DVB-T) reception card.

DVB is a registered trademark of the DVB Project. It is used with kind permission of the DVB Project and does not indicate full compliance with the relevant standards.

Background Information

Ashley BrownLee Howes

MPEG-2 Transport Streams

• Consists of a number of sub-streams, each identified by a number (its PID).

• Can contain audio, video and other data for a single programme, synchronised to one time base (a Single Programme TS or SPTS).

• Transport Streams can be multiplexed together to form a Multi-Programme TS (or MPTS).

• Each Transport Stream contains information about the PIDs and types of each audio, video or data stream.

Digital Television (DVB)

• Digital Terrestrial Television in the UK follows the DVB-T standard.

• Multiple channels are broadcast on a particular frequency, in the form of an MPEG-2 Transport Stream.

• The entire Transport Stream is processed by the receiver and the required channel extracted.

• Additional information is included in the Transport Stream to provide channel names, subtitles, digital teletext etc.

IP MulticastOnly one copy of the data is sent to the next level down in the tree, reducing network traffic

Data is only sent where it is required

Existing Solutions

• VideoLAN– Streaming of DVB channels, MPEG files,

MPEG encoder card feeds.

• DigiTV– Streaming of DVB channels.

• Digiguide– Provides 2 weeks listings and scheduled

reminders on a subscription basis. Co-operates with other programmes to allow scheduled recordings.

Our Solution

Lee Howes

Our Feature List

• Distribution of Digital Terrestrial TV channels over IP multicast.

• Selection of channels to broadcast.• Multiple TV cards.• Client Programme Guide.• Accumulation of usage statistics.• Programme recording and pausing of live

TV• Programme reminders.

Client Software

Listings Display

Main UIMPEGDemux/Display

Structure of Proposed Solution

Listings Data

Config

DVB MuxDVB Other

Sources

Main Transmission Server

Transmission (Slave) Server

Master Server

Listings Source

Listings Server

Master Configuratio

n

Stats Database

Statistics

HardwareInterface

Transmission Server

Ashley Brown

TX Server – Architecture

TRANSMISSIONSERVER

HTTP, STORED FILES

NETWORK

DVB Hardware Interface

• The server uses a Java wrapper around the C LinuxTV API for DVB devices.

• The API allows the card to be tuned and MPEG2 data (in particular a full DVB Multiplexed Transport Stream) to be read from a device.

• Support for hardware acceleration of MPEG-2 TS demultiplexing has been included, although is not used at present.

• A similar interface could be provided under Windows.

Configuration

James Robinson

Configuration• What configuration?

– Schedule– Permissions– etc.

• Required for various modules• Publish on web server

– Can use Apache authentication and SSL security

• XML Files• Configuration tool

– Creates main configuration files– Web based

Configuration - Demo

Listings Server

Lee Howes

Listings Server

XML Source

XML Source

docTV

XML Parser

Web Server

Schedule Tree

Internal Structure

XMLTV

XML Parser

XMLTV

XML Source

System Config.

Channel Selection

MPEG Decoder

Jay Cornwall

MPEG Decoder

• Java Media Framework (JMF) provides audio/visual playback support.

• MPEG 2 video decoding not supported.

• Lack of documentation and examples.• A different approach to audio/visual

decoding was taken.

MPEG DecoderJava Client

Decoding Component(Java AWT widget)

Video Decoder Audio Decoder

LibMPEG2(native library)

FFMPEG(native library)

MPEG Decoder

• 720 x 576 x 32 bit: ~30% load on an Athlon XP-M 2400+.

• Supports MPEG 2 video and MPEG 1 / 2 audio.

• Potential for further codec support.• But a loss of portability.• Restrictions on native access prevent

aspect ratio correction under Linux.

Client

Lyndon Leggate

Client

• Features– Watch live TV (if available & permitted)– Pause live feeds & resume from that point– Record programmes (scheduled or live)– Playback pre-recorded programmes– Programme reminders & auto-tune– View full TV programme listings– Usage statistics

Statistics

Simon Fothergill

Statistics

• General reasons and motivation for statistics

• Within this project: Simply, but extensibly

• When’s popular?• What’s popular?

Client

HTTP CGI

PHP SQL

PHP SQL

Stats DatabaseStats Manager Stats Collector

Putting it Together

Lee Howes

Integration and Testing

• Tested interfaces between interacting components

• Tested and integrated in stages as components developed (using VideoLAN Client initially to test the server)

• Transmission test to VLC in mid November

Integration and Testing 2

• Multiple DVB cards• General tests of listings such as

behaviour with bad date formats• Long distance unicast radio feed

to home ADSL from Transmission Server

A Few Problems…

• Initially IP multicast appeared not to work on all switches.

• A change of multicast address range solved this.

• Towards the end of the project, some faulty code resulted in the server saturating its connection.

• A faulty switch flooded the network with traffic, upsetting other services.

Evaluation

• A good start for further progress• System is flexible in design

allowing for future expansion• Substantial problems with

Java/Native interface for video could be avoided with a purely native client

Shortcomings

• Control channel not encrypted, anyone could refresh server.

• Java event thread overcrowding causing lack of GUI responsiveness.

• Current reliance on XML TV – radiotimes.com changed website format shortly before the presentation.

General Future Improvements

• DVB streaming under Windows• Digital Radio streaming (DAB)• Streaming from an MPEG encoder• Server time-shifting of channels• More configuration options• Fast, Native client, possibly using GTK to

keep cross platform• Full use of JMF to make Java client work

efficiently – not a problem in Windows, more of an issue in Linux

Feature Comparison Matrix (Server)

VideoLAN DigiTV docTV OS

DVB Yes No Yes Yes Not Yet2 No UDP No No No Yes Yes Yes MPEG Encoder

Yes No No Not Yet1 Not Yet2 No

Stored MPEG

PS Yes3 Yes3 Nearly4 Yes3 Yes3 Yes3 TS Yes Yes Yes Yes Yes Yes Audio No No No Yes Yes Yes

HTTP Sources

No No No Yes Yes Yes