[timeline] Replace default sources by as-needed-sources
Submitted by Edward Hervey
Assigned to Edward Hervey
Currently we use default sources for audio and video so that when there are gaps in the compositions, it still outputs a valid source.
With timelines getting more and more complex (and the addition of videomixer), this is costing us a lot of extra processing for nothing.
We should therefore remove the default sources and replace them by a source whenever there is a gap in the timeline.
These sources must of course not be visible in the UI.
My best guest... is to make Gaps a certain kind of TimelineObjects, which are automatically added/removed/resized whenever there is a modification in the timeline.
Removing that $#@*($@# default source is one of the essential parts to start getting decent performance in the videomixer branch.
Imported from https://bugzilla.gnome.org/show_bug.cgi?id=597131