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MPEG-4 files with audio and video generally use the standard .mp4 extension. Audio-only MPEG-4 files generally have a .m4a 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 .m4p extension.
At present, only files that are in the Windows Media (.wmv) file format may be added to your playlist. Other file types such as .mpg, .mpeg, and .avi cannot be added to the playlist. Additionally, the files must be provided by AOL. Files provided through other services cannot be added to the playlist. Clear your browser's cache
As of 2020, there has not been wide acceptance of this format, possibly due to the lack of encoders and decoders available. [8]A reference implementation of MPEG-4 ALS encoder and decoder (mp4als – e.g. mp4alsRM23) can be obtained at the MPEG-4 ALS homepage and it was also published as ISO/IEC 14496-5:2001/Amd 10:2007/Cor 3:2009.
In contrast to that, some very general-purpose container types like AVI (.avi) and QuickTime (.mov) can contain video and audio in almost any format, and have file extensions named after the container type, making it very hard for the end user to use the file extension to derive which codec or program to use to play the files.
The 'Music' category is merely a guideline on commercialized uses of a particular format, not a technical assessment of its capabilities. For example, MP3 and AAC dominate the personal audio market in terms of market share, though many other formats are comparably well suited to fill this role from a purely technical standpoint.
MPEG-4 is a group of international standards for the compression of digital audio and visual data, multimedia systems, and file storage formats. It was originally introduced in late 1998 as a group of audio and video coding formats and related technology agreed upon by the ISO/IEC Moving Picture Experts Group (MPEG) (ISO/IEC JTC 1/SC29/WG11) under the formal standard ISO/IEC 14496 – Coding ...
Audio file icons of various formats. An audio file format is a file format for storing digital audio data on a computer system. The bit layout of the audio data (excluding metadata) is called the audio coding format and can be uncompressed, or compressed to reduce the file size, often using lossy compression.
ALAC data is frequently stored within an MP4 container with the filename extension.m4a. This extension is also used by Apple for lossy AAC audio data in an MP4 container (same container, different audio encoding). The codec can also be used by the .CAF file type container, though this is much less common.