All things are possible with flash. I think fadeing out at the end and fading in at the beginning and having a actionscript command after the last frame to goto the first frame would do it..
Unfortunately, fading out at the end and fading in at the beginning does not create a seamless loop, since there are a few moments when the clip alpha is 0% and everything is completely black.This might be ok for some situations. But for creating a seamless loop, I need to have something, well, more seamless.
Actually, I think I may have come up with a possible workaround to simulate a true seamless loop of an embedded video (at least get closer to it) by placing a still image (which has been converted into a movie clip) of the first frame on a new layer at the last frame, and then copying that keyframe and pasting it about 25 frames before the end, then alpha fading from the first keyframe to the final frame.
It is not perfect, but it's something.
Perhaps someone else might have a better solution?
Who says you have to go to 0%?
If you select more than one frame in the timeline and rightclick you should see something linke "reverse Pictures/frames". This function can be easily used to create a seamless loop.
A caustics effect goes over 100 Frames (and has no seamless loop), copy frame 2-99 and insert it on the timeline behind the original. With the frames 101-198 selected choose "reverse Pictures", now you have a perfect loop