If you've got a library of video content on your hard drive dating back a number of years, there's a good chance that some of them belong to formats that aren't supported by your iOS device. In such cases, your only real option is to go through and laboriously convert such files to a compatible format.
VLC is an open source video playback app from VideoLAN that enables you to play pretty much any video file format on an iOS device. Because of its open source origins, it's free to download.
Way back at the end of 2010, the original VLC for iOS app was released onto the App Store, and then swiftly pulled due to legal technicalities.
Now the app is back on the App Store, and in an all new version 2.0 guise. The main addition relates to syncing your media to your iOS device - it's now a whole lot easier thanks to AirPlay and Dropbox support.
Subtitles are supported, as are network streams, and you can also control video playback speeds.
All you need to run VLC for iOS is an iPhone, iPad or iPod touch with iOS 5.1 or later installed on it.
VLC for iOS is available to download now on the UK App Store, and as stated it's completely free.
Read: Best Mobile Phones 2013