# Join audio files

Put 2 to 20 files together into one, in the order you choose.

Tool: Join files (`join_audio`). Price: 1 credit a minute of input for whole files, charged only when a job succeeds.

## Free API

```bash
curl -F file=@intro.mp3 -F file=@episode.mp3 -F file=@outro.mp3 https://audo.ai/api/try/join -o full-episode.mp3
```

Free for the first 3 minutes of each file, 3 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"`), the same request processes the whole file with credits. Details: https://audo.ai/docs/api.md

## Options

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

- `crossfade_ms`: A crossfade between files, in milliseconds (0 to 5000), such as 500. Default 0.
- `match_loudness`: Matches the files' loudness before joining. Default true.
- `output_format`: The result's format: same (as the first file), wav, mp3, m4a, or flac. Default same.

## 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 `join_audio`:

> Joins 2 to 20 files in order into one, such as an intro, an episode, and an outro. Use it when the person wants recordings combined. Set free to true to do the first 3 minutes of the result at no cost, up to 3 times a day; otherwise it costs 1 credit a minute of the combined length. Returns job_id; then call get_job.

Example: "Use Audo to join intro.mp3, episode.mp3, and outro.mp3, in that order."

## More

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