Almost two-thirds of digital files being swapped on file-sharing networks is video, according to P2P traffic analysts CacheLogic.

It found that eDonkey was the most popular sharing network for video.

BitTorrent saw a fall in video traffic, but more seemed to be using it to swap files which are not video or audio.

CacheLogic used sophisticated traffic monitoring techniques to analyse file extensions and track packets of data across the four main file-sharing nets.

It analysed global traffic over the main P2P services - Gnutella, FastTrack, BitTorrent and eDonkey - over a 48-hour period.

CacheLogic surmised that more "legitimate" content was being swapped over BitTorrent.

Video made up 61.4% of files on the four peer-to-peer networks. BitTorrent had the highest proportion of video traffic at 47%. Just over 42% of files on it were categorised as "other".

Such traffic could include software, software updates, or games, Nick Farka from CacheLogic told the BBC News website.

"What we found this time last year was that BitTorrent was widely used for video distribution," he said.

Mr Farka said that the fall in video and music content being swapped on BitTorrent could have been a result of the Motion Picture Association of America's (MPAA) recent legal action which specifically targeted BitTorrent tracker sites.

The MPAA had some success in getting major tracking sites closed down last year. Suprnova was the most popular of the BitTorrent tracker sites and was forced to shut in December.

"Then there are other files - CD images, software, compressed files. There has been marked shift in that mix," said Mr Farka.

But, he added, there was no real way to tell what was copyrighted, illegal content and what was not. It could be pirated software being swapped illegally, for instance.

"There are indications in as much as there is a lot of other traffic. File extensions will give some idea whether the content is legitimate or not.

"There are groups of file formats that fall into certain categories and from that we can make assumptions. We can open the packet to know the payload, but we do not know what the content is," he explained.

The report also found that 68.9% of audio files being swapped on the networks were in the MP3 format.

A surprising figure, CacheLogic said, was that 12.3% of files were in the open source audio format, OGG. The OGG format is patent and royalty free, and is supported on most media players.

Distributing bits

BitTorrent tracker sites host links to where people can find the different bits of files needed for a full piece of content.

Whole files, such as an episode of 24 for instance, are split into multiple parts. Trackers tell people the different locations where the parts of the files can be downloaded.

Download services which make use of the way file-sharing nets work are increasingly being developed to distribute legitimate content, however.

By splitting up files into multiple parts, and letting users find other users they can download the parts from, takes the bandwidth strain off of servers.

The BBC, for instance, is trialing its iMP (Interactive Media Player) which is based on file-sharing techniques.

It will let people download BBC programmes for up to seven days after they are first broadcast.

Mr Farka said file-sharing technology was something that would not disappear because it was such an effective way to give people access to large digital files.

Once set-top-boxes, such as Sky's boxes to be released in November, are hooked up to broadband connections, it is the way people will expect to get content.

"I don't think they are ever going to overcome it [file-sharing]. The way they can go forward is to embrace it.

"This is a technology that allows the distribution of content directly into people's homes," said Mr Farka.

The analysis also showed that file sizes varied between networks. Larger files tended to be swapped on eDonkey and BitTorrent. Smaller files tended to be shared on Gnutella and FastTrack.