file -i returns wrong mime type for an mp3 with integrated image-thumbnail

Question

If i enter

$ file -i music.mp3

it returns music.mp3: application/octet-stream; charset=binary

If i wipe all tags and image in this file it recognises MIME type correctly.

music.mp3: audio/mpeg; charset=binary

Is there any workaround or a bugfix? Is it possible to get correct data without modifying mp3 file?

$ file --version
file-5.03
magic file from /etc/magic:/usr/share/misc/magic

Answer 1

I was having the same problem with the same version of file on Ubuntu 10.04. I modified /etc/magic and was able to get the MIME-type of my MP3s to display as audio/mpeg. Here are the lines I added:

# MPEG Layer 3 sound files
0       beshort     &0xffe0     audio/mpeg
!:mime  audio/mpeg
#MP3 with ID3 tag
0       string      ID3     audio/mpeg
!:mime  audio/mpeg

Taken from http://www.opensource.apple.com/source/file/file-23/file/magic/magic.mime

I don't have much experience editing this "magic" directives, so I can't vouch for its effectiveness or security.

Answer 2

You can add your own rules to /etc/magic and /etc/magic.mime. See man 5 magic and the contents of /usr/share/misc/magic (or similar) for inspiration.