After a 2 year absence from the Apple App Store due to licensing issues VLC has made a comeback.
After being rewritten VLC is now bi-licensed under Mozilla’s Public License v2 and the GNU Public License v2. The VLC on the iOS store supports all video codecs that its desktop version does. VLC for iOS has also been optimized for multi-core decoding, allows WiFi synchronization as well as integration for Dropbox and network streams, and supports video filters, multiple audio tracks, and playback speed manipulation. It also supports subtitles and Airplay.
VLC works on an iOS SDK, check out the iOS on the links below.