Google is trying to salvage YouTube's image and improve the quality of discussion on the freewheeling video sharing site by allowing people to listen to their comments before they are posted.

And in a separate development that also aims to give YouTube legitimacy as a viable alternative to commercial TV, the site now contains full-length episodes of shows such as Star Trek, Beverly Hills 90210 and Dexter.

A YouTube Australia spokesman said the full-length shows were available only to those in the United States for now, but the audio preview feature was being implemented worldwide.