Please, can somebody try and load a dxv2.0 encoded video (or any other video with alpha) and apply the trails effect to check if the alpha channel is preserved?
I just tested with a Flash file on XP SP3 and an ATI 3600, and it seems that alpha is in general preserved.
However a moving object leaves a black "trail" even if the original trails are faded out already. In this case I would expect not only a RGB fade out, but also an alpha fade out.
I will test this with different files over the weekend...