Linux can't determine MIME type for 3GP, 3GPP2, etc. files?

Question

When I run

    file -bi 'filename'

in CentOS for 3GP, 3GPP2, etc. files, the return value is blank. For other files such as JPEG, GIF, MPEG, etc, the command returns the correct MIME type. Why is this so?

Thanks!

Answer 1

because the magic number for these video file type is not defined

you can take look on

man file

http://linux.die.net/man/1/file