The dropdown labeled 1 on this diagram. What is its purpose
https://userbase.kde.org/images.userbas ... 17_04b.png

Hi ttguy!

For some time we added automatic composition across tracks (any alpha channel will be used without needing to clutter the timeline view with transitions).
However this behavior can slow down a bit the program, so you can disable it with "None".
The original operation was "composite", it is quite fast, but we realized this operation slightly degrades the colors (YUV operation if I remember well?). We kept it as "Preview".
To have perfect color fidelity, JBM rewrote a composition operator (qtblend), but it can be sensibly slower (RGB conversion) so it is labelled "High Quality".

I agree with you that this mysterious setting is a usability problem, we should at least have a popup that explains the thing...

Thanks for that. I will add something to the manual on it.
I am doing some more work on the manual at the moment.

I just noticed it does have a tool tip "Track Compositing". Which makes sense now you explain it.