Johannes Taelman:
Before anyone replies with 'rtfm', I just got it to work. Do not forget a pix_rgba in your chain!
Aah, yes (slap!)! My avis are compressed, so no alpha channel without pix_rgba. Thanks. Could have thought about that by myself.
Now it doesn't crash pd. Still, I can't get no transparency via setting thresholds/pass value. Will experiment a bit. Is the position of the alpha object of any importance?
Regards,
.loop.