MP4Box

Because I'm snotty, and I hate typing commands in caps, I've got a symlink from MP4Box to mp4box on my box, hence the examples being lower case. MP4Box dumps output to stderr, so I get to be snotty in return. :D

Display information about a file, its video or audio track:

mp4box -info media.mp4
mp4box -info 1 media.mp4
mp4box -info 2 media.mp4

Set language to English on (all) tracks:

MP4Box -lang eng media.mp4

Set a title for the video (the first track). Note that I haven't been able to get things like apostrophes to work. Haven't dug much into it either, though.

MP4Box -name 1="classy video title" media.mp4

See all possible tags:

MP4Box -tag-list

Supported iTunes tag modifiers:
        album_artist    usage: album_artist=album artist
        album   usage: album=name
        tracknum        usage: track=x/N
        track   usage: track=name
        artist  usage: artist=name
        comment usage: comment=any comment
        compilation     usage: compilation=yes,no
        composer        usage: composer=name
        created usage: created=time
        disk    usage: disk=x/N
        tool    usage: tool=name
        genre   usage: genre=name
        name    usage: name=name
        tempo   usage: tempo=integer
        writer  usage: writer=name
        group   usage: group=name
        cover   usage: cover=file.jpg,file.png
        encoder usage: encoder=name
        gapless usage: gapless=yes,no
        all     usage: all=NULL