Why is firefox able to read m4a/aac file but not if embedded with HTML5?

Question

I understand that Firefox has decided not to support AAC because of licensing issue but how come is it possible to read m4a files directly in Firefox ? (I'm using 28.0)

For instance with this file :

http://www.jplayer.org/audio/m4a/TSP-01-Cro_magnon_man.m4a

(ffmpeg: Audio: aac (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 127 kb/s)

And it expectingly does not work with :

<audio controls>
   <source src="http://www.jplayer.org/audio/m4a/TSP-01-Cro_magnon_man.m4a">
</audio>

Answer 1

The embedding code above works fine for me in Firefox 28 on Windows 7.

My understanding is that while Firefox doesn't support MP4 H.264 AAC from within the software (to avoid licensing issues) it instead farms it out to OS media capabilities automatically (rather than demanding a plugin), relying on external software to deal with the licensing (at least on Windows; Linux looks like it still needs a plugin(?) https://www.mozilla.org/en-US/firefox/26.0/releasenotes/).

If you're having difficulties with m4a files online (but not locally) since upgrading to Firefox 28, I had the same issue and it turned out to be down to MIME types; our default 'audio/mpeg' seemed to work with Firefox 27, but 28 needs 'audio/mp4 m4a' or reports the files corrupted. Don't know why that would affect the above though; you could try putting the type in the source tag, see if that helps. https://developer.mozilla.org/en-US/docs/HTML/Supported_media_formats