I noticed the New AVI filesize is rather large, not to say huge.
About 385 MB for a 2 sec. RGBA HD clip.
Exporting the same clip as MJPEG compression:55 results in a 2 MB clip, and still produces a very acceptable result (or compression:100, which really looks good > 13 MB). Yet there is no Alpha (of course). Now I have to flatten my clip, turn it to black and white, export this with the same settings and use it as a track matte, when used in other applications.
Might it be an idea to have a "save track matte" checkbox (or something alike) in the AVI export setting, which will turn the clip to a black movie taking in consideration the transparancy as black?