# Add alternate audio tracks to videos
Learn how to use multi-track audio to add alternate audio tracks to your videos
## Introduction to multi-track audio

The multi-track audio feature allows you to add alternate audio tracks to the video assets in your Mux account.

Videos with multi-track audio can be used for increased accessibility or multi-language support, or just to allow viewers to opt into a different audio experience, like a director's commentary.

## (Optional) Set the language and name for your primary audio track

<Callout type="info">
  Optional but highly recommended to increase accessibility if you're delivering alternate audio tracks.
</Callout>

When you <ApiRefLink href="/docs/api-reference/video/assets/create-asset">create an asset</ApiRefLink> in Mux, you can also specify the `language_code` and `name` of the primary audio track that's embedded in your first input file.

```json
// POST https://api.mux.com/video/assets

{
  "inputs": [
    {
      "url": "{VIDEO_INPUT_URL}",
      "language_code" : "en",
      "name" : "English"
    }
  ],
  "playback_policies": [
    "public"
  ],
  "video_quality": "basic"
}
```

A `name` is optional but highly recommended. If you don't specify it, we'll generate it for you based on the `language_code` you provided. The `language_code` must be a [BCP-47 language tag](https://en.wikipedia.org/wiki/IETF_language_tag), such as `en` for English, or `es` for Spanish. You can find a list of common [BCP-47 language tags here](https://en.wikipedia.org/wiki/IETF_language_tag#List_of_common_primary_language_subtags).

You can still use multi-track audio with assets that don't have a language or name set on your initial upload; we'll just call your primary audio track "Default," with no language.

## Add alternate audio tracks to your asset

Once you've created your asset with a primary audio track, you can add alternate audio tracks using the <ApiRefLink href="/docs/api-reference/video/assets/create-asset-track">create asset track API</ApiRefLink>, specifying the URL of the audio file you wish to add, and the `language_code` of the alternate audio track. This is the same API that you can use to add captions to your assets.

Mux supports most audio file formats and codecs, such as M4A, WAV, or MP3 file.  but for fastest processing, you should [use standard inputs wherever possible](/docs/guides/minimize-processing-time).

```json
// POST https://api.mux.com/video/assets/${ASSET_ID/tracks

{
  "url": "https://example.com/bar.m4a",
  "type": "audio",
  "language_code": "fr",
  "name": "Français"
}
```

Assets must be in the `ready` state before you can use the create asset track API to add the alternate audio track.

You always need to specify the `language_code` for an alternate audio track, but the `name` is optional. If you don't specify a `name`, we'll generate it for you based on the language code you provided.

You will need to call the API once for each alternate audio track that you want to add.

## Play your videos with multi-track audio

When the alternate audio track has been processed, Mux will automatically add it to the HLS playback URL for your asset.

Many video players already support multi-track audio right out of the box, including [Mux Player](/docs/guides/mux-player-web), Video.js, ExoPlayer, and AVPlayer. So just drop your usual playback URL into your favorite video player, and click play. If your player doesn't support multi-track audio, you'll just hear the primary audio track.

Switching between audio tracks differs in each video player, but this will usually be a menu on the bottom right allowing you to change the track. For example below in Mux Player, you need to click the waveform icon.

<Player playbackId="3x5wDUHxkd8NkEfspLUK3OpSQEJe3pom" thumbnailTime="0" title="Multi-track audio demo" />