Another custom built plug-in resulting from a thread on the Apple Discussions FCP forum.

So here’s the skinny. Turns out one of Apple’s slide transitions doesn’t work ... or at least, it doesn’t work as well as it should.  A slide transition (as opposed to a wipe) doesn’t reveal the incoming clip by cropping away the outgoing clip, rather it “moves” the first clip out of the way so as to reveal the second, and this should work regardless of the contents of the clip to which it is applied.  All of Apple’s other slide transitions work correctly and consistently, but for some reason the Split Slide fails to properly handle clips with embedded alpha channels.  Whilst the effect may preview correctly, the rendered output renders any alpha as matte black thereby hiding any underlying video.

So I took a gander at the script and any genius can see the problem with Apple’s code staring them straight in the face.  Unfortunately I’m no genius and I hadn’t got a clue why it didn’t just work as it is.

OK.  So it doesn’t work properly but the other ones work perfectly, including the Center Split Slide, which splits the clip into four corners. That’ll do nicely ... a simple mod of the Center Split Slide later and I’ve two pairs of adjacent corners moving as separate halves.

This is it.  Works a treat too ... still don’t know why Apple’s code doesn’t work properly though.  Anyone?