H3 Max Recast source rules: 5 to 30 seconds, no shot over 15

The short answer

H3 Max Recast replaces the main people in a source video with the people in 1 to 4 reference photos. The source must run 5 to 30 seconds with no single shot longer than 15 seconds, and the duration you send must be the inspected length in seconds, rounded up. At the default 768p it bills $0.375 a second, so 30 seconds is $11.25.

What Recast does

Recast is video-to-video. The output keeps the source's length, motion, camera, cuts and soundtrack, and only the people change. There is no text-only mode, and aspect_ratio, frame_images, generate_audio, seed and audio references are not accepted. A prompt is optional, up to 2000 characters, and says who becomes whom or what else to keep.

The 15 second shot rule

A source of 5 to 30 seconds must also have no continuous shot longer than 15 seconds, per the catalog. A talking-head clip filmed in one take for 25 seconds is the typical case that breaks it. Cut the clip into pieces under 15 seconds at natural pauses, run each piece, and join the results in a Timeline render.

How to check a source

The route does not detect shots for you. Video inspect returns probe facts and sampled stills but not typed scenes, so look at the stills, or know your own edit points, then cut with video trim. Each trim cut is a range [start, end) from a clip on the media host.

What it costs

Billing is per second, so splitting a 24-second take into two 12-second pieces costs the same as one pass would have.

Request shape

On /v1/videos, the inputs go in input_references: exactly one video_url and 1 to 4 image_url entries, one photo per new person, left to right by default. The duration is the length you got from inspecting the source, rounded up. Do not guess it.

curl -X POST https://api.sume.com/v1/videos \
  -H "Authorization: Bearer $SUME_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: recast-001" \
  -d '{
    "model": "h3-max-recast",
    "prompt": "Replace the presenter with the person in the photo, keep everything else",
    "duration": 12,
    "resolution": "768p",
    "input_references": [
      {"type": "video_url", "video_url": {"url": "https://example.com/take.mp4"}},
      {"type": "image_url", "image_url": {"url": "https://example.com/new-presenter.png"}}
    ]
  }'