Introduction
Video Sound Effects adds a sound track to a clip by watching it. Send the footage in video_url, optionally describe what should be heard in prompt, and choose how many seconds of sound to make with duration_seconds. The tool generates effects and ambience that follow the action on screen and returns the same picture with that track as its audio.
Key features
Sound that follows the picture
The track is generated from the frames, so impacts, footsteps, pours and passing traffic land where they happen in the shot instead of on a loop laid over it. A short description steers the palette, from rain on glass to gravel underfoot to a busy kitchen, and the negative prompt keeps out what you do not want, such as music or voices.
Request parameters
| Parameter | Required | Description |
|---|---|---|
duration_seconds | No | How long the clip runs. You pay per second. ≥ 1 · ≤ 30 · Default: 8 |
guidance_scale | No | How strictly the model follows the prompt. ≥ 0 · ≤ 20 · Default: 4.5 |
ignore_visual_semantics | No | Choose the sounds from the prompt alone instead of from what the picture shows; timing still follows the motion. Default: false |
negative_prompt | No | Styles or sounds you don't want in the track. |
prompt | No | The sounds you want, as a short list. If omitted, a general request for sounds that match the on-screen action is used. |
steps | No | More steps add detail but take longer. ≥ 4 · ≤ 50 · Default: 25 |
video_url | Yes | The clip to work on. |
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.
| Option | Credits per second | ≈ USD |
|---|---|---|
| Standard | 0.18 | $0.0018 |
Each task is rounded up to whole credits, so one run at the lowest tier costs 1 credit for a 5-second clip ($0.01).
For an exact number before you run, send the same body to POST /jobs/quote.
Use cases
Finishing clips from video models
Most generated video arrives silent. Adding ambience and effects before posting makes a clip feel finished without a trip through a sound library or a session in an editor, and short clips usually come back in under a minute.
Temp sound for rough cuts and product shots
A draft that plays in silence is hard to judge.
Prompt guide & pro tips
Describe sources, not moods
List the things that make noise: espresso machine hiss, cups clinking and low café chatter work better than a cosy atmosphere. Three or four sources are plenty; long lists blur together into a wash.
Match the length to the clip
Set duration_seconds to the clip's length, rounded up.
Leave the fine controls alone at first
guidance_scale sets how closely the sound follows your words and steps sets the number of refinement passes; the defaults suit most clips. Raise guidance a little only when the result ignores the prompt, and expect more steps to take longer rather than sound dramatically better.
API quick start
Call the Video Sound Effects API in three steps
- Create an API key. Sign in to PopNow and create a key in the API console. Keys start with sk-popnow- and use the same credits as the website.
- Send the request. POST /jobs/createTask with model popnow/foley-v1/video-to-audio and an input object that follows the parameter table. The response returns a task ID straight away.
- Get the result. Poll GET /jobs/recordInfo with the task ID, or pass a callBackUrl and we post the result to it. Download the output links when the task succeeds.
# 1. Create the task. Keep the Idempotency-Key if you retry after a network error.
export IDEMPOTENCY_KEY="$(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: $IDEMPOTENCY_KEY" \
-d '{
"model": "popnow/foley-v1/video-to-audio",
"input": {
"video_url": "https://media.popnow.ai/effects/flower-bloom-1abd6efb.mp4",
"duration_seconds": 8
}
}'
# 2. Copy data.taskId from the response, then poll until state is succeeded, failed, canceled or expired.
TASK_ID="TASK_ID_FROM_RESPONSE"
curl "https://api.popnow.ai/api/v1/jobs/recordInfo?taskId=$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.
Video Sound Effects API questions
How much does the Video Sound Effects API cost?
Video Sound Effects costs 1 credit ($0.01) for a 5-second clip. Credits are the same as on the website (1 credit = $0.01), new accounts get 30 free credits, and failed tasks are refunded.
What is the model name for Video Sound Effects in the API?
Put popnow/foley-v1/video-to-audio for Video to Audio in the model field of POST /jobs/createTask.
Do I have to describe the sound?
No. Without a description, a general request for sounds that match the on-screen action is sent. A few specific words usually give a better result.
What happens to sound already in the clip?
The returned video carries the generated track as its audio, so start from a silent clip or one whose sound you want replaced.
What are the limits of the Video Sound Effects API?
Clip length: 1–30 s; Prompt length (characters): 1,000; Largest upload: 90 MB. Requests outside these limits are rejected before anything is charged.
Can I try Video Sound Effects without writing code?
Yes. The Playground runs Video Sound Effects on your PopNow credits, needs no API key, and shows the matching code for every run.