This may be a stupid question but how do you speed ramp Twixtor in FCP? I understand from the Twixtor tutorial that if you want to slow a clip down to say 20% you must line up 5 clips up against each other to create a nested sequence.

However another tutorial says you can create speed ramps by just using key framing?

http://www.revisionfx.com/content/products/twixtor/help/screencasts/twixtorfcp3speedramp.html

Why do you need to create nested sequences when it appears you can just use key framing?

Nested sequences are required because the duration of the clip can't be extended by the plugin. As such if the originating clip is 200 frames, and you slow it down to 20% of it's original speed, you need 1000 frames to show the entire clip. The way they advise to do this is to have a nested sequence with 5 of the original clips lined up one after each, this ensures that the sequence is of the correct duration. However, I imagine you could just as easily but the first clip in and a slug for the rest of the footage, because it just needs to be long enough, it doesn't actually matter what the rest of the sequence is made up of I think because you'll only ever be seeing the part of the first clip on the timeline being slowed down. (Haven't actually tested this so there may be something I am missing. Anyway generally very easy/quick to simply copy paste the original clips however many times you need.)

If you are speeding up footage, or speeding some of it up and some of it down so the total duration doesn't exceed the original clip, then you don't need to worry about this, which is probably where the any advice stating all you need is key frames is coming from. But in situations where you need a clip longer than the originating clip, you need nested sequences to get the correct total duration.

That makes sense, much appreciated Craig