Advanced Television at Low bitrates And Networked Transmission over Integrated Communication systems
An important factor in containing the costs and maintaining the technical quality of future TV production will be the ability to handle and process the video and audio signals as much as possible in compressed form. This is already happening at every stage of the television production and distribution chain, but using a chaotic assortment of different compression systems. The bridge from one compression system to the next makes decoding and recoding obligatory, leading to a progressive loss of signal quality.
The only solution with current technology is to use many more bits than strictly necessary in the earlier part of the chain, which provides sufficient "headroom" but removes most of the advantages of compression. Server and network capacities are foced to be up to ten times higher than they need to be.
In this context, ATLANTIC aims to develop the technology which will enable the signal to be kept in compressed MPEG2 format throughout the complete broadcast chain. A media server becomes a low cost PC based disk, current networks can handle many more bit-streams and the progressive loss of quality between each stage of the programme chain is largely avoided.
The main objectives of the project are therefore :
To assemble and demonstrate the essential building blocks of a programme distribution chain based on compressed video signals from the input of a studio to the final display.
To pursue international standardisation, where appropriate, for the technology demonstrated by the Project.
The Project is therefore developing :
A disc-based, MPEG2 post-production facility
A real-time mixer unit for assembling a complete MPEG2 programme stream from a selection of MPEG2 input streams
A multi-programme statistical multiplexer giving optimum efficiency across all programmes within the multiplex
A motion-compensated receiver display up-conversion suitable for high-quality, final display in an MPEG2 distribution chain
A standardised interface for the compressed signal for studio applications and for satellite, cable, and distribution equipment
Strategic VLSIs to enable economic implementation of the above functions.
Summary of Trial
The Project aims to assemble a service trial of an audio-visual programme chain based entirely on the MPEG-2 coded bit-stream in the context of EXPO´ 98 in Portugal.
The demonstration may be extended, subject to funding, to provide a programme origination and distribution infrastructure for the duration of EXPO. This would provide three programme channels to the national pavilion and to prestige video cinemas as well as ATM links to Oporto, Brussels and Geneva.
The figure below outlines the proposed demonstration.
There is also a well developed proposal to supplement the ATLANTIC demonstration by integrating the results of a number of ACTS projects in the SIC chain in an EU pavillion.
Low cost switching of the MPEG2 bit stream. This can only be achieved by the development of strategic VLSI components.
Definition of standard interfaces for compressed bit-streams which are applicable over a wide range of bit-rates and which are compatible with computer and telecom networks.
Development and implementation of effective strategies to minimise the impairments of cascading bit-rate reduction processing.
The Project has found effective solutions to the two fundamental difficulties standing in the way of the entirely MPEG2 programme chain : switching of bit-streams and bit-rate changing.
Real-time and software bit-stream switching can now be implemented to frame accuracy in video and audio without perceptible distortion. Off-line and on-line editing can now be used to assemble programmes from MPEG-2 coded bit-streams stored on a standard PC hard disk.
The ability to transcode from a higher to a lower bit-rate while maintaining a quality equal or better than coding only once at the lower rate, means that the bit-rate used in earlier parts of the chain need only be equal to or a little higher than that anticipated for final delivery. Storage and network costs are drastically reduced as statistical multiplex can be used on previously compressed material with quality loss.
It is expected that the Project will deliver an end-to-end programme chain based on the MPEG2 coded bit-stream throughout, thereby avoiding the quality impairments arising from the current practice of repeated decoding and recoding.
It is expected that this Project will lay the foundations for the economic production of television programmes in an era when the number of television channels will be increasing dramatically. Through the development of equipment using strategic VLSI devices, the functionality required for handling the MPEG bit-stream in programme production and distribution should become available at reasonable cost. The technology developed in the Project should find use in both professional and consumer-based applications.
BBC Research & Development Department
Tel: +44 1737 836613
Fax: +44 1737 836667