What does HeyGen document for its HeyGen Video model and avatar engines (limits, prompting, reproducibility, consent)?

HeyGen developer docs (captured 2026-10-23): "HeyGen Video" (heygen-video-1) is HeyGen's general-purpose video model "built on MiniMax H3 and post-trained by HeyGen" (consistent with AA listing HeyGen Video 1 at Elo 1160, $2.40/min, C3-B369-01). Modes: text-to-video, image-to-video (image is the literal first frame) and reference-to-video (reference order becomes <Picture 1>, <Picture 2>...; only the first 5 s of each reference video are read - trim to the 5 s you want). Duration 5-30 s for text/image-to-video with turbo/quality enhancement, 5-15 s for reference-to-video, ultraquality, or via MCP; resolutions 480p/768p/1080p/2k with 1080p and 2k billed at 3x the 768p rate. Prompting tips in the docs: add "no retouching, no beauty filter, no glamour lighting" to avoid retouched faces; audio is generated from the prompt, so specify room tone, effects and distance, and say "no music" to avoid an unwanted bed; set an explicit seed to make a prompt reproducible and change one clause at a time. Avatar engines: Avatar V (highest fidelity, cross-reference-driven motion and lip-sync, motion_prompt; a non-public digital-twin reference must clear its group's consent requirements), Avatar IV (default, broadest support), Avatar III (photo-to-video); custom avatar training is asynchronous. Hedra (terms + docs): does not claim ownership of inputs/outputs; v3 API with a model catalog (incl. FLUX.3, Gemini Omni Flash, ElevenLabs voice clone/isolation) and an MCP at https://mcp.hedra.com. Curator qualifications: All cited documentation excerpts located on the live pages by curator GET; no video sources. Provider documentation as served 2026-10-23; models, limits and prices change without notice. Limitations: HeyGen consent workflow details not read; prices per second not captured from HeyGen pages. Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

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  "citations": [
    {
      "url": "https://developers.heygen.com/docs/models/heygen-video.md",
      "note": "line 11; line 123 tip; line 147 tip; line 212; line 18; section 3.2"
    },
    {
      "url": "https://developers.heygen.com/avatar-v.md",
      "note": "line 11; line 123 tip; line 147 tip; line 212; line 18; section 3.2"
    },
    {
      "url": "https://www.hedra.com/terms",
      "note": "line 11; line 123 tip; line 147 tip; line 212; line 18; section 3.2"
    }
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