The BBC today launched its iPlayer web catch-up TV application for public beta test applicants. (Video demo.) The service lets U.K. users download TV programs up to seven days following their transmission date before they then expire after a 30-day window. An undisclosed set number of beta testers will be involved, with that number growing toward a November full release. Further features to be added include “series stacking”, which will download an entire season after the final episode airs, plus live TV streaming and podcasts. The BBC expects to add links to these full show downloads from its YouTube clips channel and to promo sections it hopes to build with partner media sites including Telegraph.co.uk. It’s targeting 500,000 users after six months and a million after a year.

So far, though, the release has been most notable for its platform dependency. Powered by Kontiki DRM software that to date only runs on Windows XP, the service has drawn over 12,000 signatures to a Downing Street petition campaigning for platform neutrality. The BBC Trust, which regulates the broadcaster, this week met to discuss concerns with open-source activists, but only reiterated that it would review the neutrality question every six months to ensure Mac and Linux are served at some point. Today, even some applicants who were successfully admitted to the beta test were left without a beta to test because they used Windows Vista or Mac OS X. Tech.co.uk reported many would-be testers were left disappointed. (I’m a Mac user, so can’t take part.)

Subject to lengthy regulatory approval, the iPlayer has been four years in the making, having first been proposed under the moniker “Interactive Media Player” (iMP) in 2003 - in the meantime, rival U.K. broadcasters Five, Channel 4 and most recently ITV have each launched their own on-demand web TV apps. Around 400 hours of programming (about two-thirds of the BBC’s output) will be added to the library each week.  Separately, the BBC’s year-long trial of vodcasts has come to an end and the corporation is due to decide whether to go ahead with the medium.

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