# Replace audio in video: add new sound to a video

Put a new soundtrack on any video, keeping the picture exactly as it is.

## Replace, or mix in

Replacing swaps a video's whole sound track for another file: a voiceover recorded after filming, narration in another language, a cleaned-up copy of the original sound, or music for a clip with nothing worth hearing. The picture isn't touched, so the video looks exactly as it did.

Adding music under people talking is mixing, not replacing. Take the sound out of the video, set the music under the voices in Mix audio, which can lower the music while anyone speaks, then bring the mix back here as the new sound.

Tool: Swap a video's audio (`replace_audio`). Price: 1 credit a minute of input for whole files, charged only when a job succeeds.

## Free API

```bash
curl -F video=@talk.mp4 -F audio=@talk-clean.wav https://audo.ai/api/try/swap-audio -D response.headers -o response.body
```

Read response.headers and response.body before naming media. Handle 202, 200 JSON and errors with the complete response client at https://audo.ai/docs/api#responses.

Free for the first hour of each file, 10 times a day per person, with no key or account. Uploads up to 100 MB, 2 at once from one address. The response is the result itself; a job that runs longer than about 30 seconds returns 202 with a link to check on it. With an API key (`-H "Authorization: Bearer $AUDO_API_KEY"`), omitting free runs the whole file with credits if the balance covers it, otherwise the free portion if quota remains. Set free=true to prohibit spending; for paid whole files use free=false with an approved positive max_credits. Details: https://audo.ai/docs/api.md

## Options

Form fields with the same names as the MCP tool's inputs:

- `offset_seconds`: When the new audio starts against the picture, in seconds, such as 0.5 (later) or -0.5 (earlier). Default 0.

## Languages

Any language: it works on the sound, not the words.

## From an assistant (MCP)

Add https://audo.ai/mcp and sign in (setup for each assistant: https://audo.ai/setup.md). The tool is `replace_audio`:

> Puts a new soundtrack on a video. The picture is copied, not re-encoded, so it's fast and loses nothing. Use it after processing a video's audio separately. Set free to true to do the first hour at no cost, up to 10 times a day; otherwise it costs 1 credit a minute of video. Returns job_id; then call get_job.

Example: "Use Audo to put voiceover.wav on product-demo.mp4 in place of its sound."

## More

- Every tool: https://audo.ai/llms.txt
- OpenAPI: https://audo.ai/api/openapi.json
- This page for people: https://audo.ai/replace-audio-in-video