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voice speed control for avatars in FULL mode

2 months ago by hamdy

Hi HeyGen team,

I'm implementing voice speed control for avatars in FULL mode using the rate parameter in avatar_persona, but the parameter doesn't seem to have any effect on the actual speech speed.

Implementation Details:

I'm using the LiveAvatar API v1 to create sessions with the following request:

POST https://api.heygen.com/v1/sessions/token

{
"mode": "FULL",
"avatar_id": "ffe5b6c5-e3fe-41dd-99b0-a47a7ed3107d",
"avatar_persona": {
"voice_id": "b95b2b20-5450-4bde-b1ca-8b699465fd82",
"context_id": "<my_context_id>",
"language": "en",
"rate": 0.5
}
}

UI Implementation:

Frontend has a slider control:

  • Range: 0.5 to 1.5

  • Step: 0.1

  • Default: 0.5 (slowest)

  • Labels: "Slower (0.5x)", "Normal (1.0x)", "Faster (1.5x)"

    Expected Behavior:

  • rate: 0.5 → Avatar should speak at half speed (slower)

  • rate: 1.0 → Avatar should speak at normal speed

  • rate: 1.5 → Avatar should speak 1.5x faster

    Actual Behavior:
    The avatar speaks at the same speed regardless of the rate value. I've tested with values ranging from 0.5 to 1.5, and there's no noticeable difference in speech speed.

    Debugging:

    I've confirmed:

  • ✅ The rate parameter is correctly sent in the API request (verified via console logs)

  • ✅ The API returns a successful response (200 OK)

  • ✅ The parameter type is correct (number, not string)

  • ✅ Other avatar_persona parameters work correctly (voice_id, language)

    Questions:

  1. Is the rate parameter officially supported in FULL mode for v1 sessions?
  2. Is there a different parameter name or location for controlling speech speed?
  3. Are there any specific voices or configurations required for rate to work?
  4. Could this be a known issue or limitation?

Environment:

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