As previously rumoured, Google is upgrading back catalogue films in your digital library to 4K versions. And for free.

As Apple did during the launch of the 4K version of Apple TV, Google has automatically upgraded all supported movies on its Play Movies & TV store. You will find that your own bought films should have been replaced with higher resolution versions where possible too.

That includes movies bought on HD or SD, wherever a 4K version is available.

All you need to do is open the Play Movies & TV app and it will tell you which titles have been upgraded.

In addition, 4K versions of movies on Google Play now cost less than before. You can check out Google's top 4K titles here.

It is also thought that, wherever available, 4K movies bought in future will cost the same as the HD equivalent - and play in Ultra HD on compatible devices.

Some movies also come with HDR, but it's hard to see on Google Play which ones. It makes sense to include it though, considering there are plenty of Android handsets out there now with HDR capable displays. And many 4K TVs.

Speaking of which, you can currently watch your purchased 4K movies on Sony Bravia TVs and "most" Samsung sets. LG support is coming soon.