The BBC will launch its on-demand TV service BBC iPlayer this Friday, making the software available as an open public beta for the very first time.

The broadcaster has faced harsh criticism of the service, because it is initially only available for Windows systems, though it doesn't yet work with Windows Vista.

However, the BBC has been ordered to prioritise developing a version of the service which will work with non-Windows systems, principally Mac OS X.

Under instruction from the broadcaster's governing body, the BBC Trust, the company must develop the service to be "platform-agnostic", though no time-scale for such development has yet been announced.

But the move to support Macs is seen as essential, the BBC confirmed.

"We are committed to making it as easy as possible to use BBC iPlayer. Developing a version for Apple Macs and Microsoft Vista is absolutely on our critical path," said BBC director of future media and technology, Ashley Highfield.

Highfield added: "We're also committed to making it available on the television screen, which is why we are delighted to be working with Virgin Media towards a launch on cable later this year. We are hopeful that other TV platforms will follow soon after," he said.

iPlayer is a free catch-up service for UK licence-fee payers. Users can download shows which they can store for up to 30-days. These shows integrate digital rights management (DRM) technologies which make it impossible to view archived content for more than seven days following the first view of the show.

Later this year, iPlayer will be made widely accessible across the BBC's website, as well as through links from YouTube and a number of other potential distribution partners.

The BBC is in discussion with a wide range of potential distribution partners, including MSN,, AOL, Tiscali, Yahoo!, MySpace, Blinkx and Bebo.

In time, extra features will be added to BBC iPlayer, such as streaming on-demand (allowing users to watch a programme straight away), series stacking (which allows users to download episodes from selected series retrospectively) and the highly successful BBC Radio Player.