[MPlayer-users] How programmatically determine the correct one of two english soundtracks for an encode

[Graham Lawrence]

I have a certain dvd image for which
    mplayer dvd://1 -dvd-device VIDEO_TS -identify -frames 0
gives me the following info
    ID_DVD_TITLE_1_CHAPTERS=16
    ID_DVD_TITLE_1_LENGTH=5915.467
    ID_DVD_CURRENT_TITLE=1
    There are 1 angles in this DVD title.
    audio stream: 0 format: ac3 (mono) language: en aid: 128.

    ID_AUDIO_ID=128
    ID_AID_128_LANG=en
    audio stream: 1 format: ac3 (mono) language: en aid: 129.

    ID_AUDIO_ID=129
    ID_AID_129_LANG=en
    number of audio channels on disk: 2.
    subtitle ( sid ): 2 language: en
and
    ID_AUDIO_ID=129

which last item led me to believe that "-aid 129" would encode the
audio track that matches "dvd://1"

But that was incorrect.  It should actually be "-aid 128".  So how does
one determine the appropriate soundtrack for the main title track?

-- 
Graham Lawrence