dnxhd with ffmpeg default frame-threading starts at ~0.27x realtime and
buffers a long pipeline before output flows, so the fc_pipe ring laps ~344
startup frames (spotty audio+video for the first several seconds). Setting
-threads 32 -thread_type slice makes dnxhd encode >= realtime from frame 1
(measured 1.3x at start), cutting startup drops substantially. The finalized
master file is gap-free (even PTS, audio==video duration) — the remaining
skipped frames are pre-record spin-up frames dropped to the live edge, not
holes in the recording.
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