What is your operating system?
GNU/Linux Debian testing
What is your Shotcut version (see Help > About Shotcut)? Is it 32-bit?
Shotcut 21.01.31 / 64-bit
Can you repeat the problem? If so, what are the steps?
Made 360p proxies for all my clips. The clips play fine with no lag until the playhead reaches the right of the timeline. Once it hits the right and the timeline has to move to follow the playhead it lags way too much to even watch the video anymore. I disabled audio waveforms thinking that might be a problem trying to generate them as it goes along, but that doesn’t work either. If I make the whole timeline fit within the whole screen then it plays all the way through without lag, but this is not efficient at all to constantly go back and forth zooming in and out of the timeline just to preview an edit. Is there a setting to prevent the timeline from following the playhead and let it just go off the screen? Maybe that will let me just view my edits?
The timeline view makes heavy usage of OpenGL as does the video preview, and that might be inefficient on your system - or at least the way this uses OpenGL. We do not write the OpenGL code ourselves but rather use something very high level provided by Qt, which then draws it all.
For my purposes, what I ended up doing was just use the mouse wheel to scroll the timeline as it played.
But, ultimately, I think the issue has to do with how Shotcut deals with memory when there are multiple tracks. For this project, I had to have up to five tracks playing simultaneously since it was supposed to look like a video conference call. Even using the lowest quality proxy files this was too much. Originally, I thought it would be a problem with the amount of RAM I have, and of course the more RAM the better, but then I tried doing the same in Kdenlive and, hate to say, I was able to play the five tracks simultaneously without issues.
I’ve read the post about reducing tracks to help with memory issues, but I couldn’t do that with the specific project, of course. Luckily, the project is over now. I like Shotcut so much more than Kdenlive, but I’ll just have to use both depending on the project, I guess.