While the only
filename extension defined by the standard is , various filename extensions are commonly used to indicate intended content: • MPEG-4 files with audio and video generally use the standard extension. • Audio-only MPEG-4 files generally have a (
MPEG-4 Audio) extension. This is especially true of unprotected content. • MPEG-4 files with audio streams encrypted by
FairPlay digital rights management as were sold through the
iTunes Store use the (
MPEG-4 Protected) extension. iTunes Plus tracks that the iTunes Store currently sells are unencrypted and use accordingly. •
Audiobook and
podcast files, which also contain metadata including chapter markers, images, and hyperlinks, can use the extension , but more commonly use the (
MPEG-4 Audiobook) extension. • The Apple
iPhone uses MPEG-4 audio for its ringtones but uses the extension rather than the extension. • Raw
MPEG-4 Visual bitstreams are named but this extension is also sometimes used for video in MP4 container format or in the
M4V container format. •
Mobile phones used to use
3GP, an implementation of MPEG-4 Part 12 (a.k.a. MPEG-4/JPEG2000 ISO Base Media file format), similar to MP4. It uses and extensions. These files also store non-MPEG-4 data (
H.263,
AMR,
TX3G). In practice, most (if not all) low end phones and feature phones recorded in this format, as most (if not all) other mobile phones and
smartphones record MP4 files using the .mp4 file extension, and some high end phones can record in
.raw. By the time that
4G technology was widespread, 3GP started to be phased out, and is now rarely seen. ==History==