FFmpeg Merge Videos

Endpoint

POST https://api.roasos.com/v1/assembly/merge-videos

Send your API key as a bearer token. The key needs the scope api:write. Every paid request also needs an Idempotency-Key header.

The envelope fields quote_only, quote_id, webhook_url and wait_timeout_seconds behave the same on each model endpoint. Refer to Jobs and Quotes and credits.

Good at

Stitch a batch of generated clips into one ad. Send at least two URLs and at most 12. The output keeps the smallest width and height across the inputs unless you set a frame rate.

Use this rather than Compose when you only need one clip after another with no overlay and no separate audio track.

The price is one credit, flat, whatever the clips are. fal prints $0 per compute seconds for this operation; the credit pays for the roasOS door, not for the provider.

Pricing

The unit is one operation. Pricing key: merge-videos.

The credits come from the roasOS pricing table. No other field changes the price. To get the exact price of your request, send it with quote_only: true first.

Modes

• merge-videos

Provider endpoints: fal-ai/ffmpeg-api/merge-videos.

Request fields

The schema is strict. A field that is not in this table gets 400 unsupported_option. The field names are the roasOS role names. One role has one name in every family.

Media

This endpoint accepts these media roles:

• video_urls — reference videos

Every other role is refused: avatar_id, elements, product_id, product_images, references, reference_images, image_url, end_image_url, scene_id, scene_image, video_url, audio_urls, audio_url, voice_id. A refused role gets 400 unsupported_option.

Prompt

None. This operation takes no prompt.

Send the clips in the order you want them played. Each clip must appear once: a repeated URL is refused, because on this operation it is almost always a mistake. To play one clip twice, use Compose.

Not exposed

These catalog entries describe omitted inputs, pinned values and source constraints. They do not imply that the provider accepts every listed field.

• resolution — not accepted by this public endpoint.
• resolution_aspect_ratio_video_index — not accepted by this public endpoint.

Result

The result kind is video. Always present: url.

{
  "data": {
    "id": "gen_…",
    "kind": "video",
    "model": "merge-videos",
    "status": "completed",
    "result": {
      "url": "https://cdn.roasos.com/workspaces/ws_01/result"
    }
  }
}

The files are immutable objects on https://cdn.roasos.com. A result URL is a valid media input for your next request.

Example

The three steps are always the same: quote, run, poll.

# 1. Quote. Nothing is spent.
curl -X POST https://api.roasos.com/v1/assembly/merge-videos \
  -H "Authorization: Bearer roasos_sk_live_..." \
  -H "Idempotency-Key: 0f1c9e2a-merge-videos-0001" \
  -H "Content-Type: application/json" \
  -d '{"quote_only":true,"video_urls":["https://cdn.roasos.com/workspaces/ws_01/uploads/video_urls-1.mp4"]}'
# 200 { "data": { "kind": "quote", "quote_id": "q_7Hk...", "credits": 1, "expires_at": "...",
#        "confirmation": { "model": "merge-videos", "example": "per_operation" } } }

# 2. Run. Same body, same Idempotency-Key, quote_id in place of quote_only.
curl -X POST https://api.roasos.com/v1/assembly/merge-videos \
  -H "Authorization: Bearer roasos_sk_live_..." \
  -H "Idempotency-Key: 0f1c9e2a-merge-videos-0001" \
  -H "Content-Type: application/json" \
  -d '{"quote_id":"q_7Hk...","video_urls":["https://cdn.roasos.com/workspaces/ws_01/uploads/video_urls-1.mp4"]}'
# 201 { "data": { "id": "gen_...", "status": "queued", "credits_reserved": 1 } }

# 3. Poll, then read the result.
curl https://api.roasos.com/v1/jobs/gen_.../status -H "Authorization: Bearer roasos_sk_live_..."
curl https://api.roasos.com/v1/jobs/gen_.../result -H "Authorization: Bearer roasos_sk_live_..."

Today

The endpoint is POST /v1/assembly/merge-videos.

It is live.

See also

• llms.txt for this model — the same facts as one plain-text file for an agent.
• GET https://api.roasos.com/v1/catalog/merge-videos — the machine-readable form: enums, defaults, limits and prices. Refer to the API reference.
• Jobs — how to poll a job and read its result.
• Provider endpoints: fal-ai/ffmpeg-api/merge-videos.