Combine Audio Video

Your video workflow spits out a silent clip. You've got audio from somewhere - a TTS node, a music generator, an uploaded track. This node marries the two into a single file with sound. That's it, and that's genuinely useful, because ComfyUI's core has historically been image-first and getting audio onto a render was more annoying than it should be.

How it fits the chain

CombineAudioVideo is the second half of a two-node pattern in Mixlab. First VideoCombine_Adv encodes your frames into a SCENE_VIDEO. Then this node takes that SCENE_VIDEO plus an AUDIO input and remuxes them together, handing back a new SCENE_VIDEO with the track laid in. So the typical flow is:

frames → VideoCombine_Adv → CombineAudioVideo → (save / preview)
                              audio ↑

Because it outputs a SCENE_VIDEO again, you can keep it in the Mixlab video world downstream.

The inputs - there are only two

• video - a SCENE_VIDEO. In practice this comes straight from VideoCombine_Adv. It's not a generic file path; it's the Mixlab video handle, which is why you pair these two nodes rather than trying to feed it an arbitrary MP4.
• audio - an AUDIO object, ComfyUI's standard audio type. This can come from a Load Audio node, a text-to-speech node (ChatTTS, Fish Speech), a music model, or any node that outputs AUDIO.

Output is a single SCENE_VIDEO - your clip, now with sound. It's an output node, so it also finalizes the file.

Installing it

Grab the pack. ComfyUI Manager: search mixlab, install comfyui-mixlab-nodes, restart. Or manually:

cd ComfyUI/custom_nodes
git clone https://github.com/shadowcz007/comfyui-mixlab-nodes

then install requirements (install.bat on Windows portable, or pip install -r requirements.txt) and restart.

Like every video node here, this one leans on ffmpeg - muxing audio into a container is an ffmpeg job. If ffmpeg isn't on your PATH, this node can't do its work. Install it and make sure ffmpeg -version runs from a terminal before you go hunting for bugs in the graph.

Common snags

• Audio and video are different lengths. Muxing doesn't stretch or trim to match - a 3-second clip with a 10-second track gives you one of those durations winning and the other cut off or trailing silence. Get your frame count × frame rate to line up with your audio length before this node, not after.
• No sound in the result. Almost always the audio input is empty or the source node produced nothing. Preview the audio on its own first to confirm it exists.
• It won't accept your video. The video input wants a SCENE_VIDEO specifically. Feed it VideoCombine_Adv's output, not a raw image batch or a file loaded some other way.
• ffmpeg errors in the console. Missing or broken ffmpeg install. This is the single most common cause of failure for any audio/video node in the pack.

And the standing Mixlab caveat: if the whole editor locks up (can't pan or zoom) right after you place one of these video nodes, that's a known JS conflict in the pack, not something wrong with your audio. Disabling the pack is the crude fix.