Stereo Video Mux Output

Every node in this pack builds toward something you can put on a 3D display, and this is the node that actually produces it. StereoVideoMuxOutput is the third and final link in the chain: StereoVideoSource builds the job, StereoVideoConvert renders a temporary video into ComfyUI's temp directory, and this node finalizes that temp render into a real file in your output folder, with audio and a proper stereo container.

It's deliberately boring plumbing, and that's a compliment. You plug in the rendered_video handle from Convert, decide on a name and a container, and run.

The three inputs

• rendered_video - the internal render handle coming out of StereoVideoConvert. Not a file path, just the handle; wire the two nodes together and forget about it.
• filename_prefix - the base name for the export. The node appends an incrementing counter itself, so a prefix of stereo_output gives you stereo_output_00001.mp4, then _00002, and so on. You will never overwrite a previous export, which is more than ComfyUI's default save nodes can promise.
• output_format - mp4, webm, or mkv. mp4 with h264 is the sensible default; webm if you want a leaner, open-codec file; mkv if you like poking at streams. For most 3D TV / YouTube purposes, mp4 is what you want.

The one output, output_path, is just the string where the file landed - handy if you're scripting or want to print the location in a text node.

What it does under the hood

FFmpeg muxes the temp render into the final file, and two behaviors are worth knowing about. First, it writes a stereo_mode metadata tag (left_right for SBS, top_bottom for the stacked layout) so YouTube 3D and stereo-aware players can recognize the file without you telling them what it is. Second, audio is handled based on the audio_mode you chose back on StereoVideoSource: copy trims and muxes the original clip's audio in, none writes video-only. So the audio decision isn't made here - it's baked into the job upstream, and this node just honors it. That's also why the audio always matches your selected frame range instead of the whole source clip.

Gotchas

The temp render gets deleted here as part of finalizing, by design - if you only run Source → Convert and never reach this node, the intermediate sits in your temp dir and there's no watchable file anywhere. And the audio-copy mode needs the source clip to actually have an audio track; a silent source with audio_mode = copy just produces a silent output, so pick none for clips you know are mute. Install the pack once (ComfyUI Manager search "comfyui-sbs-long-video", or git clone into custom_nodes plus pip install -r requirements.txt), and all three nodes come together.