*I think* this related to BC_COMPRESSED cinelerra's internal format. It covers both mjpeg and dv and I think raw mjpeg and may be raw dv to anything ffmpeg based now broken ... I have bug logged about mjpeg-only webcam, but no obvious (for me) solution for a/v recording, I only found way to record  strip of jpegs ... In earlier cinelerras those conversions were handled by internal quicktime copy, but this was deleted long ago because it was buggy, and hard to keep working with updated ffmpeg.

I wonder if user tried another compression type (say rawdv and not ffmpeg-based) ?