# Get Audio Track

Streams one playable track of a multi-file audiobook (folder-of-tracks
or zip-of-audio book). Track indexes and bounds come from the track
manifest on [Get Audio Chapters](get_audio_chapters.md).

**Endpoint**: `GET /api/media-items/{id}/audio/{trackIndex}`
**Auth**: Required (JWT — Bearer header or session cookie; the web
player's `<audio>` element authenticates by cookie)

## Serving

- **Folder books**: the track is served straight from its real file
  (`http.ServeContent`) — full `Range` support.
- **Zip books**: the entry is extracted in place. Forward seeks discard
  bytes in the open stream; backward seeks re-open the entry and skip
  (deflate has no random access — cheap at audio bitrates). `Range`
  requests are honored.

Single-file books have no track manifest — they stream through the
`/uploads` path exactly as before and this endpoint answers 404.

## Library visibility

The item's library must be visible to the requester; a hidden library
answers **403** on every track (same gate as the download endpoint).

## Error Responses

| Code | Description                                  |
| ---- | -------------------------------------------- |
| 400  | Invalid media item id or track index         |
| 401  | Missing/invalid token                        |
| 403  | Library not visible to the requester         |
| 404  | Book/track not found, or single-file book    |
| 500  | audio_metadata failed to parse               |

## Example

```bash
curl -H "Authorization: Bearer $TOKEN" \
  -H "Range: bytes=0-1023" \
  "http://localhost:8765/api/media-items/550e8400-.../audio/0"
```