# Audio joiner: merge audio files into one

Merge MP3s, songs, and recordings into one file, in the order you choose.

## One after another

Audo's audio joiner merges 2 to 20 files, audio (WAV, MP3, M4A, AAC, FLAC, OGG, Opus, WebM, AIFF) or video (MP4, MOV, MKV, WebM, AVI), each up to 100 MB without an account, and the first hour of the merged file is free, 10 times a day, with no sign-up. Files about 3 minutes long in all usually merge in about 7 seconds.

Merging plays your files one after another, as one file: an intro, an episode, and an outro; the chapters of an audiobook; or a recording that was saved in parts.

Files recorded at different times are often at different levels, so Make the files equally loud matches them first and nothing jumps out. A crossfade fades one file out while the next fades in, which makes the merged file a little shorter than the parts added together. To trim a file before merging, use Cut audio.

Tool: Join files (`join_audio`). Price: 1 credit a minute — $0.01/min ($0.60/hr), with no subscription — 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 -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. A free result cut short comes with finishUrl (and the Audo-Finish-Url header when the response is the file itself): give it to the person, who pays there (from $5, no sign-up), and the whole file runs; keep checking the status link, whose finishedBy names the whole-file job and its own status link. 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 hour of the result at no cost, up to 10 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