By Elizabeth Biddlecombe
The TV industry has started its march into the online world, with more and more programmes now available for download.
The future of TV is clear - for some
The US is one of the more developed markets - but what are the services like to use?
One year since Apple opened the first legal online store for television shows, it is selling more than a million TV downloads a week.
Amazon, AOL and Google have also entered the business and the major US TV networks have started to embrace the medium.
ABC offers its biggest shows online
ABC is currently home to some of TV's most popular shows - such as Desperate Housewives, Dancing with the Stars, Grey's Anatomy and Lost.
It is also, as Jupiter Research analyst Todd Chanko comments, "the most prominent [of the TV networks] in its display of online video".
That includes numerous short clips as well as full episodes from six ABC shows. For most shows, the most recent four episodes are available, although all episodes in the current season of Lost are online while it is off air.
Everything is free - but click on an episode and the first thing you get is an advert. There are three 30-second ad breaks in each programme, which is less intrusive than normal television but more than other ad-free download services.
The player window can be maximised without compromising the picture quality. Since this is a streaming service, the only thing that can throttle the performance is the network connection. Other than that, the main browsers are supported and the service works on both PCs and Macs .
Besides iTunes, ABC.com is the only place to find these hit shows on the web - legally at least. It is also one of the most accessible and instant ways to watch a TV programme online, albeit from a limited selection of shows.
iTunes is one of the most popular online TV stores
Apple currently has more than 250 TV shows in the iTunes store. It also has the second largest number of users of all video sites, behind YouTube, according to Nielsen NetRatings.
ITunes certainly allows some freedom. There are no adverts, the show stays on the hard drive indefinitely and, of course, can be transferred to the video iPod for easy viewing.
But first the user must download the iTunes software to even browse the selection, although the software makes it easy to find titles and allows the user to preview before they buy.
Shows cost $1.99 (£1) each but there are passes for a whole season or multi-passes for daily shows. You can also buy programmes to give as gifts.
Apple has increased the resolution of its video so it is "near-DVD quality" at a resolution of 640 x 480 pixels. In our test, the picture pixelated in full-screen mode but looked good at three quarters of the screen.
AOL has many archive programmes such as Joey
AOL has full TV episodes on its In2TV service, which is free but includes adverts.
Content is divided into channels like LOL TV for comedy and or DramaRama TV for drama. Sixty-five shows are listed, none of which are current season favourites.
For instant gratification, viewers can watch a programme as a stream from the In2TV site. Or for a better quality image, they can download the show - as long as they have AOL's Hi-Q Delivery Manager software. The download programme expires after about two months.
As with some other online television services, AOL also makes short TV clips available on its website. It has also seen some success with its made-for-the-web reality TV show, Gold Rush.
In2TV is only available to PC users using Windows XP.
Amazon has been criticised for restrictions
With each episode costing $1.99 (£1), Amazon's prices for its new Unbox service are comparable with iTunes.
The service has other similarities as well. There are no adverts. Special software must be downloaded - Amazon's Unbox video manager - although the user browses shows on the Amazon website.
TV shows from Unbox can be put on up to two portable devices - but only devices that run the Microsoft Plays for Sure copyright scheme.
The shows will therefore not play on an iPod, and nor does Unbox run on a Apple computer.
Purchased shows can be downloaded onto two different computers and burned to DVD, but only for back-up purposes.
Amazon's service has been panned by users because of these restrictions.
Other normal Amazon features apply to Unbox. For instance, regular purchasers can buy with one click and the system makes suggestions for other purchases.
The latest episodes of some current shows are available - an Amazon spokesperson says the catalogue goes "thousands" deep. But there are some obvious gaps - no Desperate Housewives, for instance.