Actually, it's movie_play() as shown below.
int rval = movie_play(full_name);
if ( !rval ) {
char str[256];
sprintf(str, XSTR( "Unable to play movie %s.", 204), Cutscenes[which_cutscene].name );
popup(0, 1, POPUP_OK, str );
In this case, int is used like a boolean to tell if the function succeeded and full_name is a char* with the full file name of the movie to play. This function does not exist in the source code we have so the above code is commented out. The big trick I think is finding some sort of library/headers/whatever that we can use with GCC under Cygwin and, maybe, Linux. Haven't looked at any DIVX libraries or whatever yet so I'm not sure how easy it'd be to drop it in there. And there may be licensing issues for some stuff, if it's GPL, 'cause we aren't in control of the license used for the FS2 source.