# Start an upload

> Page: https://docs.flung.dev/reference/api/post-v1-media. Index of every page: https://docs.flung.dev/llms.txt

Reserves a file and says how to send it: one PUT to `uploadUrl` up to 100 MB, or `multipart` parts for a larger video (give `bytes`).

`POST /v1/media`

## TL;DR

| Question | Answer |
|---|---|
| What does it do? | Start an upload. |
| What does it need? | An API key or an OAuth access token. |
| What does it take? | A JSON body with the fields below. |
| What does it return? | Status 201 with a body of type [`MediaUpload`](https://docs.flung.dev/reference/api/schemas.md#mediaupload). |
| In the SDK? | `flung.media.create()` |
| What can go wrong? | `401` Missing, unknown, revoked or expired API key; `422` The request failed validation; `429` Too many requests for this credential; wait for `retry-after` seconds. Every failure has the same [error shape](https://docs.flung.dev/reference/api/errors.md). |

## What it does

Reserves a file and says how to send it: one PUT to `uploadUrl` up to 100 MB, or `multipart` parts for a larger video (give `bytes`). Use the id in `mediaIds` once the file is `ready`.

## Example

**curl**

```bash
curl -X POST 'https://api.flung.dev/v1/media' \
  --header "Authorization: Bearer $FLUNG_API_KEY" \
  --header 'Content-Type: application/json' \
  --header "Idempotency-Key: $(uuidgen)" \
  --data '{
  "contentType": "image/jpeg"
}'
```

**TypeScript**

```ts
import { Flung } from '@flung.dev/sdk'

const flung = new Flung({ apiKey: process.env.FLUNG_API_KEY! })
const result = await flung.media.create({
  contentType: 'image/jpeg',
})
```

**fetch**

```js
const response = await fetch('https://api.flung.dev/v1/media', {
  method: 'POST',
  headers: {
    'Authorization': `Bearer ${process.env.FLUNG_API_KEY}`,
    'Content-Type': 'application/json',
    'Idempotency-Key': crypto.randomUUID(),
  },
  body: JSON.stringify({
    contentType: 'image/jpeg',
  }),
})
if (!response.ok) throw new Error((await response.json()).error.message)
const result = await response.json()
```

A successful answer looks like this:

```json
{
  "id": "med_aaaaaaaaaaaaaaaaaaaaaaaa",
  "contentType": "image/jpeg",
  "filename": "string",
  "bytes": 1,
  "status": "pending",
  "preview": {
    "status": "processing",
    "thumbnailUrl": "string",
    "hlsUrl": "string",
    "dashUrl": "string",
    "durationSeconds": 1
  },
  "createdAt": "2026-11-01T09:00:00.000Z"
}
```

## Request body

The body has the type an object, with the fields below.

| Field | Type | Required | Description |
|---|---|---|---|
| `contentType` | `any` | yes |  |
| `filename` | `string` | no | at least 1 character; at most 255 characters. |
| `bytes` | `integer` | no | The file's size. Required over 100 MB, which then uploads in parts. minimum 1. |

## Responses

| Status | Meaning | Body |
|---|---|---|
| 201 | The reserved file and its upload address. | [`MediaUpload`](https://docs.flung.dev/reference/api/schemas.md#mediaupload) |
| 401 | Missing, unknown, revoked or expired API key. | [`Error`](https://docs.flung.dev/reference/api/schemas.md#error) |
| 422 | The request failed validation. | [`Error`](https://docs.flung.dev/reference/api/schemas.md#error) |
| 429 | Too many requests for this credential; wait for `retry-after` seconds. | [`Error`](https://docs.flung.dev/reference/api/schemas.md#error) |

## Response body

A 201 answer has the type [`MediaUpload`](https://docs.flung.dev/reference/api/schemas.md#mediaupload).

| Field | Type | Required | Description |
|---|---|---|---|
| `id` | `string` | yes |  |
| `contentType` | `MediaType` | yes | What the file really is, read from its first bytes once uploaded. |
| `filename` | `string \| null` | yes |  |
| `bytes` | `integer \| null` | yes |  |
| `status` | `"pending" \| "processing" \| "ready" \| "failed"` | yes | `pending` until its bytes arrive; `ready` once a post can use it. |
| `preview` | `object \| null` | yes | Videos only, where previews are set up: a thumbnail. Read the file again while `processing`. |
| `preview.status` | `"processing" \| "ready" \| "failed" \| "skipped"` | yes | `skipped` when the video is over 100 MB or this month's thumbnail allowance is used up. Posts never wait for a preview; they use the file as uploaded. |
| `preview.thumbnailUrl` | `string \| null` | yes | A JPEG frame one second in, 640 pixels wide, at an address that does not expire. |
| `preview.hlsUrl` | `string \| null` | yes | Always null for now: streaming versions are not made. |
| `preview.dashUrl` | `string \| null` | yes | Always null for now. |
| `preview.durationSeconds` | `number \| null` | yes | Always null for now. |
| `createdAt` | `string` | yes |  |
| `uploadUrl` | `string \| null` | yes | For a file up to 100 MB: PUT it here, with your credential and its Content-Length. Null for a multipart upload. |
| `multipart` | `object \| null` | yes | For a file over 100 MB: how to send it in parts. |
| `multipart.partSize` | `integer` | yes | Every part but the last is exactly this many bytes. |
| `multipart.partCount` | `integer` | yes |  |
| `multipart.partUrl` | `string` | yes | PUT each part to this address with `{partNumber}` replaced by 1 to partCount, in any order. |
| `multipart.completeUrl` | `string` | yes | POST here once every part is in. |

## See also

| Doc | Why |
|---|---|
| [API reference](https://docs.flung.dev/reference/api.md) | Every endpoint |
| [Schemas](https://docs.flung.dev/reference/api/schemas.md) | Every request and response type |
| [Errors](https://docs.flung.dev/reference/api/errors.md) | Every error code and what to do about it |