RafaMar wrote:
...but I think it would be easier with an effect that instead of acting on the track acts on a single clip. A clip that we can define with cuts if we only want to change the speed to a fragment of it.
Yes, I also thought the same thing. If were possible tecnically, it would be better and easier from point of view of an user.
Another NLE, Lightworks_14, had done a good solution for me. Each track has a Speed text field that shows the speed of the clip where the cursor is on. When you change the speed of a clip, that clip will have that speed; you can not to do Speed ramp, for example.

In these days I am working on a Project that needs Speed fetures. To do that I use both ReframeRT and F_tmix plugins to create a fake SlowMotion (with Optical Flow) and then, with the Nest feature, I put the ClipSpeed in the Timeline. For some clips I have to use ffmpeg by command line and using "minterpolate" option to made OpticalFlow. Maybe there is Optical Flow in Cinelerra-gg but I do not know where. If anyone knows, He/She is welcome, please.
I use Nest to avoid sync problem with the other edits on the Timeline when I use ReframeRT for the speed.
I hope GG can make the Speed tool work well.
(Ooops, I wrote here but this it Forum stuff. Sorry)

IgorBeg