You do need to make the clip as long as the FINAL duration you want.
[Maciek] “However the clip in the timeline still only takes up 10 seconds and shows 1/4 of the footage. It seems like the clip should be 4 times as long now.” As a way around i can imageine tha making 75% of the frames blank at the end but it seems like a long way of doing it.
Plugins in AE are not allowed to make the clip longer. So you do have to make blank frames in one way or another.
You can do this in the following manner:
Put your clip into a composition of the final duration (call this the intermediate comp). Then put the intermediate comp into another comp (the Final comp) and apply Twixtor to the intemediate comp that’s inside of the final comp.
This is explained here: https://www.revisionfx.com/auxdocs/ExtendDuration.htm (which you are referred to by the Twixtor manual).
Another way to do it that is only documented in the Twixtor tutorials (sorry, it should be in the manual too).
Drop your clip into a comp (the intermediate comp). Apply Twixtor and leave the speed setting at 100% (we will retime using AE’s time-remapping or time-stretching tools so leave the Speed% setting at 100%). Put the intermediate comp into another comp (the final comp). Apply time remapping or time stretching inside of the final comp. This uses AE’s tools to redo the timing, but uses Twixtor to do the actual interpolating. Make sure to turn OFF frame blending.
This method is shown in the sample projects found here https://www.revisionfx.com/rstwixtortutorials.htm, Download the Twixtor 4.5 tutorials in the “More sample projects” section. The sample project you want to look at is the 3_AudioAndVideo.aep project. Make sure to read the short description in the TwixtorAEExamplesReadme.htm file).
Pete Litwinowicz