While saving, most (all?) control api calls take >100ms.

[DDR0]

Reproduction: Start a save. Make an API call. It usually takes a hair over 100ms.

This caps the UI to running at about 9fps, which is far from our target 30.

[oskirby]

There are two possible causes that you might experience a loss of framerate during a file save. The first is that we can easily hit 100% CPU utilization depending on the encoding format and storage media being used, and the second is that the D-Bus API is blocked during gstreamer state changes, which can take several seconds to complete.

If the drop in framerate is due to the CPU load then there isn't really anything we can do about it without sacrificing filesave performance.

If the drop in framerate is due to the API blocking during state changes, then I suggest you try out a copy of the chronos-video package of version 0.4.0~alpha38 or newer, which should now split the D-Bus API off into its own thread.