MPEG-4 Part 14 or MP4 file format, formally, is a multimedia container format standard specified as a part of MPEG-4. It is most commonly used to store digital video and digital audio streams, especially those defined by MPEG, but can also be used to store other data such as subtitles and still images. Like most modern container formats, MPEG-4 Part 14 allows streaming over the Internet. A separate hint track is used to include streaming information in the file. The official filename extension for MPEG-4 Part 14 files is .mp4, thus the container format is often referred to simply as MP4.
Some devices advertised as "MP4 players" are simply MP3 players that also play AMV video and/or some other video format, and do not play the MPEG-4 part 14 format.
Almost any kind of data can be embedded in MPEG-4 Part 14 files through private streams. The registered codecs for MPEG-4 Part 12-based files are published on the website of MP4 Registration authority (mp4ra.org), but most of them are not widely supported by MP4 players. The widely-supported codecs and additional data streams are:
* Video: MPEG-4 Part 10 (also known as H.264/MPEG-4 AVC), MPEG-4 Part 2, (other compression formats are less used: MPEG-2, MPEG-1).
* Audio: Advanced Audio Coding (AAC - a subpart of MPEG-4 Part 3), (other compression formats are less used: MPEG-1 Audio Layer III (MP3), Apple Lossless, MPEG-4 Part 3 Audio Object Types: Audio Lossless Coding (ALS), Scalable Lossless Coding (SLS), MPEG-1 Audio Layer II (MP2), MPEG-1 Audio Layer I (MP1), CELP, HVXC (speech), TwinVQ (very low bitrates), Text To Speech Interface (TTSI), SAOL (MIDI) and others.
* Subtitles: MPEG-4 Timed Text (also known as 3GPP Timed Text). Some private stream examples include Nero's use of DVD subtitles (Vobsub) in MP4 files.