> ## Documentation Index
> Fetch the complete documentation index at: https://comfytv.org/llms.txt
> Use this file to discover all available pages before exploring further.

# Mux Audio

> Attach an audio track to a clip — either replacing the original sound or mixing on top of it.

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  <img src="https://mintcdn.com/comfytv/dMkMxJDZdIo4YzAU/images/nodes/_placeholder.svg?fit=max&auto=format&n=dMkMxJDZdIo4YzAU&q=85&s=b54171099e5b02d4313fe581171ebbcc" alt="Mux Audio" width="800" height="450" data-path="images/nodes/_placeholder.svg" />
</Frame>

## What this node does

**Mux Audio** combines a video with a separate audio source into one clip. It takes a
`COMFYTV_VIDEO` and a `COMFYTV_AUDIO` and, on **▶ Run**, muxes them (PyAV / ffmpeg) into a new
MP4 saved as a project snapshot. It needs **both** an upstream video and an upstream audio, or
the run errors out. The output is `COMFYTV_VIDEO`.

## When to use it

* Drop a music bed or voice-over onto a silent (or to-be-replaced) clip.
* Swap a clip's original audio for a cleaned-up or dubbed track.
* Mix generated speech / sound design over existing footage audio.

## Parameters

### mode

How the incoming audio meets the clip's existing audio:

* **replace** (default) — discard the clip's original audio and use the incoming track only.
* **mix** — blend the incoming track together with the clip's original audio.

### offset\_s

Shift the incoming audio in time, in seconds. Range **−600 to 600**, step 0.05, default
**0.0**. Positive delays the audio (starts later); negative pushes it earlier. Use this to
sync a voice-over or music to the picture.

## Inputs and outputs

| Port            | Type            | Meaning                                                 |
| --------------- | --------------- | ------------------------------------------------------- |
| **video** (in)  | `COMFYTV_VIDEO` | The clip whose picture you keep.                        |
| **audio** (in)  | `COMFYTV_AUDIO` | The audio track to attach.                              |
| **video** (out) | `COMFYTV_VIDEO` | The clip with the new/mixed audio, saved as a snapshot. |

## Tips

* Both inputs are required — a missing video or audio raises an error.
* Use **replace** when the source audio is unwanted; use **mix** to keep both (e.g. ambience
  plus a music bed).
* Nudge **offset\_s** in small steps to line up speech with lip movement.

## Bridge note

`COMFYTV_VIDEO` and `COMFYTV_AUDIO` are project snapshot references, not native ComfyUI
tensors. To move between ComfyTV and native ComfyUI nodes, insert a **Bridge**
(`ComfyTV/Bridge`). See [https://github.com/jtydhr88/ComfyTV/blob/main/docs/bridges.md](https://github.com/jtydhr88/ComfyTV/blob/main/docs/bridges.md).

## Related nodes

* **Video Volume** — set the clip's own audio level before mixing.
* **Video Concat** — assemble the sequence, then mux a single soundtrack across it.