Beyond the stock transitions that have to be downloaded from Apple’s webpage you can create your own, but doing this turned out to be a bit of a challenge, as the documentation is almost non-existent and I haven’t ever done something this way. I have keyframed wipes with videos that had alpha channels, but I had never used the “alpha transition” transition that was new with FCP 7. So… here was my process. I created this wipe in after effects – I thought it would work great with our weekly announcement video “the pulse”.
After looking at a few ariticles online I was only further lost as to how to actually make it work, I tried about 20 times at black/white mattes and finally came up with a combo that worked.
You need to have the white be the part of the transitioning video that shows and the black is the part that is transparent (like this)
Thirdly, you need to have a video clip actually give instructions as to when or how the video goes from (clip a) to (clip b) and that is what this third clip is for.
The important thing on this clip is that white is your (clip a) or the video/image your transitioning away from and the black is the incoming video/image.
I hope this sort of makes sense, I write things like this down so I can remember better and maybe I can help someone else along the way.