Amazon has launched a video download service, selling films, TV episodes and video content from over 30 studios to US customers. 

The online retail giant is promising that its Amazon Unbox service will offer DVD-quality downloads. The service was first reported at the end of July.  

Amazon Unbox will provide three video files with each purchase, one encoded at 2,500Kbps using the VC-1 Advanced Profile codec, one optimised for playback on any Windows Media-compatible portable device, and a progressive download allowing users to start watching a movie within five minutes of ordering.

"Amazon Unbox offers TV and movie enthusiasts a fast, convenient way to watch thousands of their favourite videos from around the world," said Bill Carr, vice president of digital media at Amazon.com.

"Now Amazon.com customers can choose to get videos delivered to their doorstep from Amazon's DVD store, or choose Amazon Unbox and download DVD-quality movies or television shows to their PC."

The service will include popular TV content such as CSI and Numb3rs from CBS and 24 and Prison Break from Fox. Classic series such as Buffy the Vampire Slayer, Firefly and Star Trek will also be available. 

Amazon Unbox will feature content from channels such as A&E, Cartoon Network, Discovery, FX, Comedy Central, Nickelodeon, MTV and VH1. 

US users will also be able to watch popular UK shows from the BBC such as Coupling. 

TV episodes will cost $1.99 each while movies will sell for between $7.99 and $14.99 or be available to rent for $3.99.