Seedance 2.0 Fast API

Introduction

Seedance 2.0 Fast Video extend continues a clip you already have. Send it as video_url, and add a prompt for what happens next if you want to steer it. The final frame of your clip becomes the opening frame of a new Seedance 2.0 Fast image-to-video shot of 4 to 15 seconds, and the two are joined into one MP4: your original first, then the continuation, with the repeated seam frame removed. The new segment also comes back as its own file, so you can keep extending or edit the pieces separately.

Key features

Continuity comes from the last frame. Wardrobe, set, light and where everyone stands carry over because the new segment literally starts on your final frame. Motion does not carry over the same way: the model sees one still, not the whole clip, so describe the movement you want to continue instead of assuming it will keep its speed or direction.

You choose how it ends. last_image_url is optional: give it and the new segment lands on that image, leave it out and the model decides. The prompt is optional too, so a one-click extend works without writing a word.

One file back, plus the new piece on its own. The first output asset is the joined clip (role video) and the second is the new segment alone (role segment), ready for another extend or for an editor. Sound from your source stays; sound generated for the new segment follows it; a silent side is padded with silence so picture and sound stay in step at the seam.

Everything else is Seedance 2.0 Fast image-to-video.

Request parameters

Pricing

Prices are in credits, the same credits you use on the website (1 credit = $0.01). The hold is taken when the task is accepted and settled to the actual charge when it finishes; failed tasks are refunded.

Each task is rounded up to whole credits, so one run at the lowest tier costs 34 credits for a 5-second clip ($0.34).

For an exact number before you run, send the same body to POST /jobs/quote.

Use cases

Lengthen a shot that ended too early: a product turntable that stops before the label faces camera, or a walk that cuts before the subject reaches the door. Extend it by a few seconds and describe only the remaining motion.

Build a longer sequence step by step. Because every step starts from a single frame, watch each seam before stacking the next one.

Prompt guide & pro tips

Describe the next beat, not the whole scene. The frame already fixes who and where, so spend the prompt on the action that follows and the camera move, and name the sound you want. Repeat the camera language your clip ended on, such as a slow push in or a locked shot, so the seam reads as one take.

Trim before you extend. The last frame is the only thing the model sees, so a blurred, mid-cut or heavily compressed ending carries straight into the continuation. Cut your source on a clean, sharp frame first. Sources of up to 60 seconds are accepted as MP4, MOV or WebM.

The framing of the new segment follows the last frame of your clip, so there is no aspect ratio to choose; expect a close match to the source, not a pixel-exact one. If the model returns a noticeably different shape, the new segment is scaled to fill your frame and centered, cropping what spills over.

API quick start

Call the Seedance 2.0 Fast API in three steps

1. Create an API key. Sign in to PopNow and create a key in the API console. Keys start with sk-popnow- and use the same credits as the website.
2. Send the request. POST /jobs/createTask with model bytedance/seedance-2.0-fast/video-extend and an input object that follows the parameter table. The response returns a task ID straight away.
3. Get the result. Poll GET /jobs/recordInfo with the task ID, or pass a callBackUrl and we post the result to it. Download the output links when the task succeeds.

# 1. Create the task. Keep the Idempotency-Key if you retry after a network error.
export IDEMPOTENCY_KEY="$(uuidgen)"
curl -X POST https://api.popnow.ai/api/v1/jobs/createTask \
  -H "Authorization: Bearer $POPNOW_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: $IDEMPOTENCY_KEY" \
  -d '{
  "model": "bytedance/seedance-2.0-fast/video-extend",
  "input": {
    "video_url": "https://media.popnow.ai/effects/flower-bloom-1abd6efb.mp4",
    "resolution": "720p",
    "duration_seconds": 5,
    "generate_audio": true
  }
}'

# 2. Copy data.taskId from the response, then poll until state is succeeded, failed, canceled or expired.
TASK_ID="TASK_ID_FROM_RESPONSE"
curl "https://api.popnow.ai/api/v1/jobs/recordInfo?taskId=$TASK_ID" \
  -H "Authorization: Bearer $POPNOW_API_KEY"

Replace the prompt and any links with your own. The API tab has the response, polling and callback reference.

Seedance 2.0 Fast API questions

All Seedance models

Seedance 2.0 Mini has the same settings and is the cheapest tier; full Seedance 2.0 adds 1080p and 4K.

• Seedance 2.5 APIByteDance's newest: 30-second clips with native audioFrom 56 credits for a 5-second clip
• Seedance 2.0 Mini APILightweight Seedance for quick 720p drafts with soundFrom 9 credits for a 5-second clip
• Seedance 2.0 APICinematic clips up to 4K with native audioFrom 33 credits for a 5-second clip
• Seedance 2.0 Fast APIFaster Seedance 2.0 with sound at 720pFrom 17 credits for a 5-second clip
• Seedance 1.5 Pro APINative-audio clips with an optional locked cameraFrom 9 credits for a 5-second clip

Other video APIs

• MiniMax H3 APIExpressive clips with audio, up to 2KFrom 28 credits for a 5-second clip
• Kling 3.0 API4K clips, multi-shot cuts and motion controlFrom 51 credits for a 5-second clip
• Vidu Q4 Preview APIUp to 4K clips with sound and spoken dialogueFrom 34 credits for a 5-second clip
• Wan 3.0 APIUp to 30-second clips with synced audioFrom 34 credits for a 5-second clip
• Kling O3 APIKling’s unified model: create, animate, reference and edit up to 4KFrom 51 credits for a 5-second clip
• MiniMax H3 Max APIFast clips with ambience, effects and musicFrom 38 credits for a 5-second clip

More about Seedance 2.0 Fast

Try it

Seedance 2.0 Fast AI Video Generator onlineCreate videos with Seedance 2.0 Fast in PopNow

Docs

Seedance 2.0 Fast model ID and input schema in the API docsPopNow API quickstart: your first request in five minutesImage to video guide for the PopNow APIWebhooks: get Seedance 2.0 Fast results without polling