MasterAudioMux (terminal mux-LAST, -c:a copy)

OTR_MasterAudioMux is the terminal node - the last thing that runs before a finished episode lands in output/otr/obs/. Its job is deliberately narrow, and the narrowness is the point: it's the only node in the pack that adds audio to the final video, and it does it with -c:a copy - the audio stream is copied byte-for-byte, never re-encoded.

Why does that matter? The pack's whole architecture is "audio is the source of truth": a frozen 48 kHz master defines the episode timeline, and the video is rendered to fit it. If the mux re-encoded the audio, that frozen master would silently drift - the very thing the pipeline's determinism discipline exists to prevent. So the rule is structural: video renders silent (OTR_SilentComposite), captions and credits burn in, and only here does the master WAV get muxed onto the video, untouched.

How it works

Two required inputs: silent_video_path (the always-silent composite from OTR_SilentComposite) and master_audio_path - the frozen master WAV from OTR_EpisodeAssembler.output_path, copied with -c:a copy. No -shortest flag, and a byte-identical assert after the mux: the pack verifies the audio that went in is the audio that came out.

The ordering gate is audio_done (EpisodeAssembler's out3) - wire it and the mux is guaranteed to run after the audio freezes. And declared_credits_tail_s is the credits-aware guard: OTR_CreditsRoll declares how long its silent tail runs, and the mux's tail guard permits a video that's v <= audio + declared + tolerance. If you skip that wire, the guard falls back to the OTR_MAX_CREDITS_TAIL_S env ceiling - which is how you'd get a legitimate render refused for "video too long."

One retired connector to ignore: clip_manifest_json is kept only for topology compatibility - it's hashed by IS_CHANGED but has no effect on the output. Setting it does nothing.

Inputs and output

Also optional: fps (25), ffmpeg (binary on PATH), and output_path - empty defaults to <output>/otr/episodes/<stem>_final.mp4. Outputs: final_video_path and report.

Install and gotchas

Pack-level install (ComfyUI Manager → ComfyUI-OldTimeRadio, restart; v2.0-alpha). Needs ffmpeg on PATH - that's the one system dependency the whole video side leans on. The realistic gotcha: if your final MP4 has no audio, check you fed it the master WAV and not some intermediate clip - this node is the single point where audio joins, so a silent final almost always means the wrong path got wired into master_audio_path. And if the render refuses over a too-long video with credits, wire declared_credits_tail_s from the credits node instead of fighting the guard.