.m4a is considered audio/m4a or audio/mp4

ios audio core-audio
Brosef picture Brosef · Oct 6, 2016 · Viewed 10k times · Source

I'm trying to make an audio upload to S3 and I'm a little confused what I should declare my mime type as. My audio file is an m4a recorded on an iphone as kAudioFormatMPEG4AAC. Would this be considered audio/m4a or audio/mp4? I'm seeing conflicting answers online.

Answer

Tim picture Tim · Oct 6, 2016

The m4 in m4a is short-hand for MPEG-4, just like mp4 is short-hand for MPEG-4.

In fact, m4a, m4v and mp4 files all have the same internal MPEG-4 atom structure. The difference between the files is their content (video files have video atoms as well as audio atoms.)

The codec of the audio can also be different despite using the same file extension, for example both alac and AAC formats use the MPEG-4 container format with the m4a file extension.

So to answer your question, it really doesn't make much difference. My personal preference would be audio/mp4 since that is effectively saying

Audio data in MPEG-4 container

Whereas, audio/m4a is like saying

Audio data in MPEG-4 container containing audio

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