Definition:
.mp4 is the official file extension of the multimedia container format MPEG-4 part 14, which is the digital audio or digital video portion of MPEG-4. Because its file extension is .mp4, MPEG-4 Part 14 is often referred to simply as MP4. MP4s can actually contain multiple audio, video and subtitle streams as they are container formats and not simple file formats.
MPEG-4 files with both audio and video most commonly use the .mp4 file extension, but those with audio-only might use the file extension .m4a instead.
.m4a is one of the file formats that the PSP can play.
Pronunciation: em pee for
Also Known As: MPEG-4 Part 14, MP4
Examples:
The PSP can play both audio and video files in .mp4 format.
