More info:
– this problem is recent. Using older files originated with the same camera and ingested using the same path and procedures, I can successfully generate QuickTime reference files today.
– the recently-generated QuickTime reference files (that don’t work): when played back in the QuickTime player, these files have no video and the audio is a series of tones and static. Older QuickTime reference files playback with audio and video in the Player.