Just like MPEG-1, 2, 3, MPEG-4 is also a compressive method of audio and visual (AV) digital data. It was introduced in 1998 and served as a standard for a group of video and audio coding formats. MPEG-4 is used widely in compression of AV data for web (as streaming media) and CD distribution, voice (for telephone and videophone), and broadcast television applications.
MPEG-4 also features open in source, and so companies and institutes develop different formats due to MPEG-4 standard. The popular video formats like WMV9, QuickTime, DivX, Xvid, etc. are all under the standard of MPEG-4.
MPEG-4 encoding is widely accepted by most of the devices. If you have some special format files that you want to play back on your mobile devices, you can just think of converting videos to MP4 files. And then you can freely watch videos on your devices.