setComposition
Loads a composition, or replaces the current one, suspending until it is presentable.
Cheap to call repeatedly with a changed value. An equal composition does nothing, a change confined to effect parameters updates the live pipeline and redraws, and only a structural change rebuilds: clips added, removed, reordered, or a trim that changes duration. Debounce structural edits so a drag-reorder issues one rebuild rather than thirty.
Return
whether the composition loaded, failed, or was superseded by a later call.
Parameters
The composition to present, the same value that goes to export.
Where to start, or null to hold the current position.
Whether playback should start once the composition is presentable. False leaves a playing preview playing, and only pause stops one.
The callback form of setComposition, for callers without coroutines.
Return
a handle that cancels the request.
Parameters
What to load, and how.
Receives the outcome exactly once.