Poor timeline zoom/scroll performance with long audio thumbnails present
Since the 2019 refactor release, performance of the timeline is poor when a very long (e.g. 9-hour) clip is in the timeline if audio waveforms are enabled. Disabling audio waveforms resolves the performance issues, so the audio waveforms seem to be the culprit of the poor performance.
The performance issues manifest as significant lag and unresponsiveness of the entire application when attempting to zoom in the timeline (Ctrl + Scroll) and scroll the timeline left and right (Scroll Up/Scroll Down).
Going back to a pre-refactor version (18.12.1), the same clip does not cause any performance issues zooming and panning the timeline with audio waveforms enabled. Olive 0.1.2 also doesn't have any trouble zooming and panning the timeline with this clip and audio waveforms enabled.
While it's unlikely that a single clip of this length would be present in a finished project, it's very common in my workflow to have clips this long that I need to cut down to more reasonable sizes, and I've been essentially unable to work with them in post-refactor Kdenlive due to the lag. I can provide a sample clip if that would help.