Yet more TV-related shows have debuted on iTunes in the US, this time from HBO's globally successful series, 'The Sopranos'.

As it prepares to launch the sixth season of the series, the network is offering video interviews with the cast, show summaries, behind-the-scenes footage and audio clips through Apple's service. Complete shows aren't being released just yet.

HBO has also introduced similar content for three other shows: 'Big Love', 'Rome' and 'Entourage'.

The network is available on subscription only in the US. It's believed the decision not to release entire shows through iTunes reflects the complexity of ensuring the network's subs and DVD revenues aren't impacted, reports Television Week.

However, another subscription channel, Showtime, has begun releasing entire shows through iTunes - and is seeing success, a spokesman said: "The iTunes downloads are creating a new revenue stream for the company while expanding the universe of consumers who can view our shows through this platform."