Amazon.com has rolled out a video on demand service that offers users ad-free movies and television shows on Macintoshes or PCs.

Amazon Video on Demand updates the company's Unbox application, which allowed users to watch videos on a PC or on TiVo digital video recorders. The updated system lets users access 40,000 movies and TV shows via their Web browser and download them using the Unbox application.

In addition, the system provides the option of renting or buying movies and TV shows directly through Sony's Bravia Internet Video Link Device on compatible Bravia TVs.

"The ability to watch content instantly without downloading first was among the most requested features of our customers, and now it's live--customers can instantly watch the ad-free title of their choice on a Mac, PC or compatible Sony Bravia TV," said Roy Price, director of Amazon Video On Demand, in a statement.

The new service also lets users watch the first two minutes of a movie or TV show before they opt to buy or rent it. And once a user orders a video it is added to a library that can be accessed via browsers on Macs and PCs.

David Chartier, a blogger with ArsTechnica, called Amazon's second pass at a digital video distribution effort (after Unbox) an overall success.

"As efforts like Hulu and all the individual networks make the browser a more compelling video medium, it's clear that more consumers than ever are happy to stream content to their computer displays," he noted. "The uniqueness of Amazon's approach with Video on Demand can also not be underestimated, as it may very well have struck a good balance between 'owning' content and not having to manage it. With the ability to purchase content, but not have to download it-and requisition all the storage space it requires-customers can access their content from almost any high-speed Internet connection."

However, he also cited problems with the initial version of the new service, including the lack of a support for high-definition content, which he described as a "deal breaker" for many users.

"Further, a complicated download and rule system probably won't get any iTunes Store customers to toss out their iPhones and iPods anytime soon, especially since Video on Demand is primarily designed and marketed so heavily as a streaming service," he added.

"Amazon has proven that it is very interested in the digital video distribution market, so we're expecting a major push behind Video on Demand and an adaptive strategy to make it an appealing service."

Liz Gannes a blogger with NewTeeVee, added that the new service will bridge current offerings from iTunes, Hulu and Netflix.

"[Amazon] beats iTunes on TV because it has NBC, and it beats Hulu on movies because it has far more of them," she added. Netflix's movie service, meanwhile, only provides streaming for PCs."