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# Music Short

Trim a section of a song and mux it with a 9:16 cover into a YouTube Short. Asynchronous — returns a job ID that you poll.

```
POST /api/v1/youtube/music-short
```

Supply a public `audio_url`, a public 9:16 `image_url` cover, and the trim window (`start_sec`/`end_sec`, ≤ 60s). We mux them into a 1080×1920 MP4 on the clip worker. The call returns a `job_id`; poll [`GET /api/v1/jobs/{id}`](/vdocs/video-api/jobs.md) until `status` is `completed`, then download from `/api/v1/jobs/{id}/video`. Flat charge per successful short; refunded on failure.

## Authentication

```
Authorization: Bearer sk_live_...
```

Requires the `youtube` product entitlement. See [Authentication](/vdocs/authentication.md) for details.

## Bring your own cover & captions

On the API, the cover image and any captions are **customer-supplied**. Generate a 9:16 cover with the [Thumbnail API](/vdocs/youtube-tools-api/thumbnail-generate.md) (or host your own), and pass word-pop captions as an array if you want them burned in. Auto cover-generation and auto-transcription are panel-only.

## Request

**Content-Type:** `application/json` (or `multipart/form-data` to upload the audio/cover files directly instead of hosting them yourself).

| Field       | Type   | Required           | Description                                                                                                                                                               |
| ----------- | ------ | ------------------ | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `audio_url` | string | ✅ (JSON lane)      | Public https URL to the song.                                                                                                                                             |
| `image_url` | string | ✅ (JSON lane)      | Public https URL to a 9:16 cover image.                                                                                                                                   |
| `audio`     | file   | ✅ (multipart lane) | The song file, uploaded directly instead of `audio_url`.                                                                                                                  |
| `image`     | file   | ✅ (multipart lane) | The 9:16 cover image file, uploaded directly instead of `image_url`.                                                                                                      |
| `start_sec` | number | ✅                  | Section start in seconds (≥ 0).                                                                                                                                           |
| `end_sec`   | number | ✅                  | Section end (> `start_sec`, at most 60s after it).                                                                                                                        |
| `captions`  | array  | —                  | Optional word-pop captions: `[{ word, start, end }]` with times relative to the section (0 = `start_sec`). Max 2000 entries. In multipart, pass as a JSON-encoded string. |

## Response

```json
{
  "job_id": "V1StGXR8_Z5jdHi6B-myT",
  "status": "queued",
  "charged_cents": 25,
  "balance_cents": 4975,
  "poll_url": "/api/v1/jobs/V1StGXR8_Z5jdHi6B-myT"
}
```

HTTP status: `202 Accepted`.

Poll [`GET /api/v1/jobs/{job_id}`](/vdocs/video-api/jobs.md) every 5–10 seconds until the job completes or fails, then download the finished MP4 from `/api/v1/jobs/{job_id}/video`.

## Example

```bash
# 1. Submit
curl -X POST https://substance-api.com/api/v1/youtube/music-short \
  -H "Authorization: Bearer sk_live_..." \
  -H "Content-Type: application/json" \
  -d '{
    "audio_url": "https://example.com/song.mp3",
    "image_url": "https://example.com/cover_9x16.png",
    "start_sec": 42,
    "end_sec": 72
  }'

# 2. Poll until completed, then download
curl https://substance-api.com/api/v1/jobs/JOB_ID \
  -H "Authorization: Bearer sk_live_..."
```

## Errors

| Status | When                                                                                                                    |
| ------ | ----------------------------------------------------------------------------------------------------------------------- |
| `400`  | Missing/invalid `audio_url`/`audio` or `image_url`/`image`, bad trim window, section over 60s, or malformed `captions`. |
| `401`  | Missing/invalid API key.                                                                                                |
| `402`  | Insufficient balance.                                                                                                   |
| `403`  | Account doesn't have the `youtube` product enabled.                                                                     |
| `502`  | The short couldn't be started. Balance is refunded — see `refunded_cents`.                                              |
| `503`  | Pipeline temporarily offline.                                                                                           |

Jobs that fail mid-pipeline return `status: "failed"` when polled and are refunded automatically. See [Errors](/vdocs/errors.md) for full details.

## Pricing

Billed per call — see [Credits & pricing](/vdocs/account/credits.md) for current rates.


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