Cameron Cordes
42453d5786
The concat stage wrote to <key>.mp4.tmp (for an atomic publish-rename), but ffmpeg infers the muxer from the output extension and can't map .tmp to a format — "Unable to choose an output format". Force the mp4 muxer explicitly so the temp extension is irrelevant. Segment render, NVENC, TTS, and scripting were already working end-to-end; this was the only failure, at the final join. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>