Mp4 Extensions

While the only formal filename expansion described by the conventional is .mp4, various filename additions are widely used to indicate designed content:
MPEG-4 information files with movie and sound usually use the conventional .mp4 expansion.
Audio-only MPEG-4 information files usually have a .m4a expansion. This is especially true of non-protected material.
MPEG-4 information files with sound sources secured by FairPlay Digital Privileges Management as were marketed through the iTunes Shop use the .m4p expansion. iTunes Plus paths, that the iTunes Shop currently offers, are unencrypted and use .m4a accordingly.
Audio book and podcast information files, which also contain meta-data such as section indicators, pictures, and backlinks, can use the expansion .m4a, but more usually use the .m4b expansion. An .m4a sound information file cannot "bookmark" (remember the last hearing spot), whereas .m4b expansion information files can.[dubious – discuss]
The The apple company iPhone uses MPEG-4 sound for its ring-tones but uses the .m4r expansion rather than the .m4a expansion.
Raw MPEG-4 Visible bitstreams are known as .m4v but this expansion is also sometimes used for movie in MP4 package structure.[21]
Mobile mobile phones use 3GP, an execution of MPEG-4 Aspect 12 (a.k.a. MPEG-4/JPEG2000 ISO Platform Press information file format), similar to MP4. It uses .3gp and .3g2 additions. These information files also store non-MPEG-4 information (H.263, AMR, TX3G).
.MP4 compared to .M4A
M4A appears for MPEG 4 Audio and is a filename expansion used to signify music.
The lifestyle of two different filename additions, .MP4 and .M4A, for labeling audio-only MP4 information files has been a source of misunderstandings among customers and multi-media play-back application. Some information file supervisors, such as Microsoft windows Traveler, look up the media kind and associated programs of a information file depending on its filename expansion. But since MPEG-4 Aspect 14 is a package structure, MPEG-4 information files may contain any number of sound, movie, and even subtitle sources, making it difficult to figure out the kind of sources in an MPEG-4 information file depending on its filename expansion alone. In reaction, The apple company Inc. started using and making popular the .m4a filename expansion, which is used for MP4 bins with sound information in the lossy Innovative Audio Programming (AAC) or its own lossless The apple company Lossless (ALAC) types. Software able of audio/video play-back should identify information files with either .m4a or .mp4 filename additions, as would be predicted, since there are no information structure variations between the two. Most application able of creating MPEG-4 sound will allow the customer to choose the filename expansion of the created MPEG-4 information files.

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