even simple transitions like dissolve cause the framerate to go anywhere from 35-60 all the way down to a slideshow. Not sure why this is, but I'm using the latest build (as of Feb 27th on Arch).

In my tests, even though I only have a few older versions, I did find it working more as expected on an April 4, 2017 cinelerra-gg version. It is odd because with a 30fps file, if I watch "Framerate achieved" in Settings->Preferences, Playback A tab, the framerate stays pretty much at 30fps then goes down to 12fps during the transition and then up to 140fps to catch back up -- not what you would expect to see. GG will have to investigate this further. gg/phyllis