ffmpeg 8.x's concat filter kept dying with the opaque
[fc#0] Error sending frames to consumers: Invalid argument
even after we locked fps + sample rate + pixel format + SAR in the
filter graph. Mixed sources (AV1+H.264, 23.98+60 fps, 44100+48000 Hz,
tv-range+unspecified-range pixel format) just don't survive the
concat filter cleanly in this build.
Switch to the more reliable 2-pass pattern:
1. At the trim step, re-encode each segment to a uniform intermediate
spec: libx264 ultrafast, 1920x1080 (letterboxed), yuv420p,
seqFps target rate, 48kHz stereo AAC. Per-segment ffmpeg.
2. At the concat step, use the concat *demuxer*. Because every input
now matches exactly, the demuxer is well-behaved. Transcode the
concatenated stream to the final target codec (ProRes 422 HQ etc).
Costs an extra intermediate encode (libx264 ultrafast ≈ realtime on
this hardware) but eliminates the filter-graph fragility on mixed-
source timelines, which is the workload that actually matters.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
686b90294b