generate_audio false on Gemini Omni: accepted, clip keeps its audio

If you send generate_audio: false to gemini-omni-flash-1.1 on Video Router, the request is accepted and the clip still carries native synced audio. For minimax-h3 and minimax-h3-max the same flag is a 400: "model minimax-h3 always produces native stereo audio; omit generate_audio." For grok-imagine-video-1.5 it is refused because that model takes no such field.

Docs and code differ on Gemini Omni

The Video Router docs page says native audio is always on and that the API rejects generate_audio: false. The validation code on main does something different: it accepts the flag as a no-op. A code comment explains why. A caller that pinned both the model and generate_audio: false for b-roll could not satisfy a rejection, and it caused many wasted create calls, so the flag is accepted and has no effect. The schema tests assert both true and false parse for this model. Trust behaviour you have observed over a sentence on a docs page, and read the code or test when it matters.

How to get a silent result

If you need picture without sound for an edit, do not rely on the flag for the always-on models. Pick a model whose catalog entry offers an audio toggle, and verify the result: video_inspect on a stored clip returns probe.has_audio, and a frames: false inspect is enough to read it.

Guard in the client

The snippet encodes the three behaviours so a pipeline stops asking for something the model will ignore or refuse. It prints a decision and sends nothing.

ALWAYS_ON_IGNORED = {"gemini-omni-flash-1.1"}
ALWAYS_ON_REFUSED = {"minimax-h3", "minimax-h3-max"}
NO_FIELD = {"grok-imagine-video-1.5"}

def audio_plan(model: str, want_audio: bool) -> str:
    if want_audio:
        return "omit the flag; sound is on" if model in ALWAYS_ON_REFUSED | ALWAYS_ON_IGNORED else "send generate_audio true"
    if model in ALWAYS_ON_REFUSED | NO_FIELD:
        return "do not send the flag; choose another model"
    if model in ALWAYS_ON_IGNORED:
        return "flag is ignored; the clip keeps its audio"
    return "send generate_audio false"

for m in ("gemini-omni-flash-1.1", "minimax-h3", "kling-3"):
    print(m, "->", audio_plan(m, False))

When not to trust a silent flag

Always listen to the output, or probe its streams, before you build a timeline on the assumption that a clip is mute. A no-op flag is worse than a loud error because nothing tells you it did nothing. The same goes for the Gemini Omni reference rules: it takes images and short videos but no audio references, and aspect ratio is limited to 16:9 or 9:16.

If your pipeline reads a model's capabilities at start-up, treat "audio: true with no toggle" as a distinct state from "audio: true with a toggle". The first means the clip will have sound whatever you send, which affects mixing, loudness and licensing checks downstream.