This file allows the soundtrack for movies to be overriden.
The first column is a symbolic name.
The second column is the name of the MVE file to override the soundtrack for.
The third column is the name of the WAV file to use as the soundtrack.
In BG2 ToB we have:

 2DA V1.0
 NONE
           OVERRIDE   SOUND_OVERRIDE 
ENDMVE1    OUTRO      OUTGood    
ENDMVE2    OUTRO      OutEvil    
ENDMVE3    OUTRO      OutNeutr