BBC Research and Development is co-operating with the commercial broadcaster ITV on a technical trial to deliver high-quality audio and video over the internet by making their channels available for the first time as multicast streams.

Although the BBC has previously experimented with multicast streams, notably for the Olympics, this is the first time that television channels have been made available continuously in this way.

It could pave the way for the whole country to be able to watch television over the internet, although that is still “a long, long way away,” according to Tom Loosemore, head of strategic innovation at the BBC. “We want to offer live telly eventually and so this is clearly one area where we’re trying to help the UK internet become ready for that.”

The channels available in the technical trial include the four main BBC television channels plus News 24, and the four main ITV commercial networks. The channels are being provided in a variety of formats, with the BBC television networks available in both MPEG-2 at 5Mbps and MPEG-4 H.264 at around 1.2Mbps. The ten BBC national radio networks will also be available, including feeds using the AAC advanced audio compression scheme.

At the moment, these services will only be accessible in the UK for rights reasons, and only to a limited number of users on multicast enabled networks.

Most audio and video on the internet are currently unicast, meaning that each user receives a unique stream. This ultimately limits the number of users that can be supported.

Multicast is more like broadcasting, effectively allowing many users to join or ‘tune’ to a particular channel. This is the basis of delivering live channels in an IPTV or internet protocol television system.

Unfortunately, many networks, including the main BT network in the UK, do not currently support multicast. For this reason, the forthcoming BT broadband television service will be a hybrid, with users receiving live channels over the air as a conventional digital terrestrial television transmission. BT is planning to invest billions in a next generation network that will eventually support multicast.

However, some internet service providers already enable multicast. These include JANET, the main academic network in the UK, and a limited number of broadband service providers that operate their own networks. These networks are able to ‘peer’ directly with the BBC network at the main London internet exchange to receive the multicast channels.

“This unique opportunity to trial multicast technology with internet service providers and users will give us valuable insight into usage patterns and help to test this innovative and scalable solution to broadcasting over the internet,” said Simon Fell, controller of emerging technologies at ITV.

The project is being run by a small team at BBC R&D, led by Brandon Butterworth, who was one of the pioneers of the BBC’s first internet services.

The BBC has provided streaming media services since the mid-nineties, but has been limited to delivering tens of thousands of simultaneous streams at comparatively low resolution and quality. The use of multicast approaches could ultimately support hundreds of thousands or millions of users with high quality audio and video.