With a high-res loop (1600x800) scaled on a 1280x1024 composition, brightness is very low, and there is a kinf of big pixel on the details of the video.
I did a test with the same resolution and same loop on GrandVJ, and wow ! see the difference :

The loop is exactly the same (even if I have not made a printscreen at the same position in the video, brightness is constant on all the timeline)
Video loop is quicktime animation with alpha channel.
Is there a way to solve this -very- boring problem ????
Thanx !