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Old 01-17-2004, 09:21 PM   #1
Registered: Jan 2002
Location: Missoula. Montana, USA
Distribution: Slackware (various)
Posts: 457

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file magic for m4a (mp4) ??

I have some audio files I acquired that are in m4a format, which I understand is the same as mp4. I can play or convert these with mplayer, and it provides the following information on them:

Playing audio.m4a
MOV: File-Type unknown Major-Brand: M4A
QuickTime/MOV file format detected.
MOV track #0: 305 chunks, 6405 samples
Audio bits: 16 chans: 2 rate: 44100
MOV: Found MPEG4 audio Elementary Stream Descriptor atom (51)!
Fourcc: mp4a

Most of my audio files are mp3 or ogg ... I use a script that parses the outfile of "file <audiofile>" to decide whether to use ogg123 or mpg321 for playback. Unfortunately, the output of "file audio.m4a" is "audio.m4a: data", rather unilluminating and I'ld rather not feed something that may destroy my soundcard, speakers (not to mention ears) through mplayer. While I can (and do) use the extension for identification, I prefer the more elegant solution of a file type identifier like the command "file". Anyone have a file command that works on these files, or have any suggestions besides my current hack.

Old 01-23-2004, 09:21 AM   #2
LQ Newbie
Registered: Jan 2004
Distribution: debian
Posts: 2

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Sure, I like to (mis)use the file command for such things also.
For the time being you can edit /etc/magic, that's the file 'file' uses for personal settings, for the format see 'man magic' or the database located in /usr/share/misc/file/magic.* it's pretty straightforward.
(and you can do several neat things with it like parsing the bitrate and such, see the database for examples)


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