Model Details
Seedance 2.0 Fast turns a written prompt into a short video clip with a matching soundtrack — dialogue, ambience, and sound effects are generated together with the picture rather than dubbed on afterwards, so what you hear lines up with what moves on screen. It is the quick, lower-cost tier of Seedance 2.0: the same synchronized audio, 4 to 15 seconds at 24 fps, and seven frame shapes from widescreen to vertical and 21:9 — but capped at 720p, about a fifth cheaper per second, and noticeably faster to return. Prompts are understood in English, Chinese, Japanese, Indonesian, Spanish, and Portuguese.
## Best for - Iterating on a prompt cheaply before you commit to a final render - High-volume clip production where cost per second matters more than maximum detail - Vertical, square, and widescreen social cuts where 720p is enough - Short ad, trailer, and b-roll shots that need sound without a separate audio pass - Dialogue and singing shots where the voice has to match the mouth
## Choose another model when - You need 1080p or the best picture quality in the family — use `bytedance/seedance-v2/text-to-video` - You want the cheapest clip and 720p is fine — `bytedance/seedance-v2-mini/text-to-video` is the lowest-cost tier - You already have the photo you want to animate — use `bytedance/seedance-v2-fast/image-to-video`, which takes your still as the first frame - You need several reference images for character consistency, a pinned first and last frame, or a restyle of existing footage — those are top-tier only: `bytedance/seedance-v2/reference-to-video`, `bytedance/seedance-v2/first-last-frame`, `bytedance/seedance-v2/video-to-video` - You need runs reproducible from a fixed seed — there is no seed input, so two identical prompts give different clips
## Tips - Describe the sound as explicitly as the picture ("gulls calling, waves on shingle") — the audio track follows the prompt - Set `generate_audio` to false for a silent clip; the price is the same either way - Draft at `480p`, then re-run the keeper at `720p` — resolution is the largest cost driver and duration the second - Put camera language in the prompt ("slow push in", "handheld follow") — there is no separate camera control
## Limitations - Fast motion and crowds smear at 480p; 720p holds detail better - Prompts stacking many separate shots drift in character, wardrobe, and lighting - Text rendered inside the frame is frequently misspelled
To run via the ModelRunner JavaScript client: ```js import { modelrunner } from "@modelrunner/client";
const result = await modelrunner.subscribe("bytedance/seedance-v2-fast/text-to-video", { input: { prompt: "A lighthouse keeper climbs the spiral stair at dawn, lamp glass catching the first light, gulls calling outside as the storm clears", resolution: "720p", aspect_ratio: "9:16", duration: 6, generate_audio: true, }, }); ```


