remotion-dev/remotion · error · TypeError

onModelLoadProgress must be a function.

Error message

onModelLoadProgress must be a function.

What it means

separateVideoLayers validates its options before doing any work. If you pass onModelLoadProgress and it is not a function (and not undefined), a TypeError is thrown immediately during option validation. This callback is supposed to receive model download/loading progress (0-1), so anything other than a callable would silently break progress reporting, hence the strict check.

Source

Thrown at packages/video-matting/src/separate-video-layers.ts:232

			options.keyframeIntervalInSeconds <= 0)
	) {
		throw new TypeError(
			'keyframeIntervalInSeconds must be a positive finite number.',
		);
	}

	if (
		options.onProgress !== undefined &&
		typeof options.onProgress !== 'function'
	) {
		throw new TypeError('onProgress must be a function.');
	}

	if (
		options.onModelLoadProgress !== undefined &&
		typeof options.onModelLoadProgress !== 'function'
	) {
		throw new TypeError('onModelLoadProgress must be a function.');
	}
};

const makeInput = (src: string | URL | Blob): Input => {
	const source =
		typeof src === 'string' || src instanceof URL
			? new UrlSource(src)
			: new BlobSource(src);

	return new Input({formats: ALL_FORMATS, source});
};

const probeVideoInput = async ({
	input,
	videoQuality,
}: {
	input: Input;
	videoQuality: Quality;

View on GitHub (pinned to b2f4e34732)

Solutions

1. Remove the onModelLoadProgress property entirely if you don't need progress reporting (undefined is allowed).
2. Pass an actual function, e.g. (progress) => console.log(progress).
3. If the value comes from user config, default it: onModelLoadProgress: cfg.cb ?? undefined, and reject non-function config values before calling.

Example fix

// before
await separateVideoLayers({src, onModelLoadProgress: null});
// after
await separateVideoLayers({
  src,
  onModelLoadProgress: (progress) => setProgress(progress),
});

if (opts.onModelLoadProgress !== undefined && typeof opts.onModelLoadProgress !== 'function') {
  throw new TypeError('onModelLoadProgress must be a function or undefined');
}

const isProgressCb = (v: unknown): v is (p: number) => void =>
  typeof v === 'function';

When it happens

Trigger: Calling separateVideoLayers({src, onModelLoadProgress: <non-function>}) — e.g. onModelLoadProgress: true, a string, a number, or null (null is not undefined, so it fails the check).

Common situations: Passing null intending 'no callback'; passing a promise-returning value or a config object instead of the callback; typo like onModelLoadProgres leaving a stale value; reading the option from untyped config/JSON input.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• forceTranscode must be a boolean.
• outputs.${layer} must be an object.
• Argument missing for parameter "frame"
• Argument passed for "frame" is not a number: ${frame}
• You have passed a volume of type ${typeof props.volume} to y

AI-assisted analysis of remotion-dev/remotion@b2f4e34732 (2026-09-09). Data as JSON: /api/errors/62af9477ba76ea5f. Report an issue: GitHub.