As reported in March, Sky's NOW TV subscription service is making good on the promise of supporting as many streaming devices as possible by adding Google Chromecast support for its apps for Android, iPhone, iPad and iPod touch.

The NOW TV apps for both platforms have been updated to include a new button in the top-right hand corner to stream content from its Sky Movies, Entertainment and Sky Sports packages to a TV through the Google dongle device. Unfortunately though, much-requested support for Airplay to an Apple TV is yet to be realised.

The answer as to why that hasn't arrived with the ability to Chromecast perhaps lies in the method each external device uses to stream content. Google's Chromecast device does not take its video stream from the device used to cast it, rather directly from the internet itself. The casting works more like a remote control to tell the Chromecast dongle what stream to pull from the 'net.

Apple TV works by receiving video content stored or streamed through an iOS device. The content is therefore pulled from the internet by the iPad or iPhone in question and then sent through a home network to the set-top-box. And it is this essential difference that could make it fall foul of content licensing laws.

We've previously heard at Pocket-lint that content cannot be transmitted through the air by anyone other than the original licensee. This is apparent with services like the Virgin Media TiVo box, which does not allow users to watch content recorded on their hard drives on a wirelessly connected tablet or smartphone. It is technically possible, but is tied up in licensing red tape.

It is our understanding therefore that while Apple TV cannot have Sky or NOW TV content streamed to it through a home network, a Chromecast can show the same content as it is effectively pulling the content from source in much the same way as a videogames console, Smart TV, Roku or NOW TV's own box do.

Pocket-lint has contacted NOW TV to clarify and will update when we hear back.

Also, one word of warning about Chromecast streaming. We've discovered that it will count as one device on your maximum of four able to be linked to a NOW TV account. The device you are streaming from doesn't when streaming to Chromecast, but will if you want to watch NOW TV content on the tablet or smartphone too.