Overlapping compose clips crossfade

A compose track plays one clip at a time, so two clips that overlapped on the same track could not both be placed where they started. The render pushed the second clip to after the first, the track ran past the end of the timeline, and the job failed as RENDER_INCOMPLETE after rendering the whole thing. The usual way to hit it was a music bed looped as two clips, the second starting a second before the first ends.

Two clips that overlap with no transition between them now crossfade over the overlap, the same as writing a crossfade transition item of that length between them. Picture dissolves, sound blends at constant power, and the track ends where its last clip ends.

• What you see. validate returns a warning on the second clip’s start that names the overlap and both fixes. A render that did this says so in the render step’s clipOverlaps, next to clipOverruns.
• To choose the blend. Put a transition item between the two clips. The overlap you placed is the length it plays.
• To cut instead. Start the second clip where the first ends.
• Two documents are refused at submit now, with the path and the fix, instead of rendering in full and then failing: a hard cut (transition: "none") between clips that overlap, and a clip that starts before the previous clip on its track.

Nothing changes for clips that meet, leave a gap, or already have a transition between them. Those documents render exactly as before.

Transitions and clip timing are covered in the compose docs.