Compose zooms and pans stop flashing black

A long compose render with an animated transform could come out with one fully black frame somewhere in the middle. It lasted a thirtieth of a second at 30 fps, landed in a different place on every render, and the job still reported complete.

• What triggered it. A clip whose transform is keyframed or uses animateTo: a slow zoom on a still, a pan, an animated crop. Clips with a fixed position and size were never affected.
• How often. Rarely per frame, so short videos almost never showed it. On a 15-minute slideshow of 113 zooming stills it appeared in 5 of 7 test renders before the fix and in none of 10 after.
• What changes for you. Nothing in your timeline. Render time is the same, and frames that were correct before are identical now.

If you re-rendered a long video to get rid of a stray dark flash, one render is enough again.

Keyframes and animateTo are covered in the compose docs.