remotion-dev/remotion · error

Cannot interpolate an input which is not a number

Error message

Cannot interpolate an input which is not a number

What it means

Thrown by interpolate() after the undefined check and range validation, when typeof input !== 'number'. Because undefined is already caught earlier, this fires for other non-number inputs: strings, booleans, objects, null, bigint, symbols, and functions. NaN does not hit this (typeof NaN === 'number') but is handled by extrapolation/clamping downstream.

Solutions

1. Coerce the input with Number() and confirm the result is a finite number.
2. Type the variable as number upstream so the bad value is caught at compile time.
3. Guard the call site to skip interpolation for non-number inputs.

Example fix

// before
const r = interpolate(frameStr, [0, 1], [0, 100]); // frameStr is a string
// after
const r = interpolate(Number(frameStr), [0, 1], [0, 100]);

if (typeof input !== 'number') {
  throw new Error('input must be a number');
}
const r = interpolate(input, inputRange, outputRange);

const isNumber = (v: unknown): v is number => typeof v === 'number';

When it happens

Trigger: interpolate('0', [0,1], [0,100]); interpolate(null, [...], [...]); interpolate(true, [...], [...]); passing a frame value read from a string source without coercion.

Common situations: Reading the current value from a DOM input or URL param (string) and passing it uncoerced; passing an object that wraps a number; null from an optional chain.

Related errors

• input can not be undefined
• must contain only numbers
• outputRange must contain only numbers
• outputRange must contain only numbers, numeric tuples, or…
• outputRange tuples must contain only finite numbers, but got

AI-assisted analysis of remotion-dev/remotion@46a3a6bf13 (2026-09-18). Data as JSON: /api/errors/9da1ecd64c39cf82. Report an issue: GitHub.

Appendix: source

Thrown at packages/core/src/interpolate.ts:1315

		throw new Error(
			'inputRange (' +
				inputRange.length +
				') and outputRange (' +
				outputRange.length +
				') must have the same length',
		);
	}

	checkInfiniteRange('inputRange', inputRange);
	checkValidInputRange(inputRange);

	assertValidInterpolateEasingOption(options?.easing, inputRange.length);
	assertValidInterpolatePosterizeOption(options?.posterize);
	assertValidInterpolateOutputOption(options?.output);
	assertValidInterpolateOutputType(options?.outputType);

	if (typeof input !== 'number') {
		throw new TypeError('Cannot interpolate an input which is not a number');
	}

	if (!Array.isArray(outputRange)) {
		throw new Error('outputRange must contain only numbers');
	}

	const outputType = options?.outputType;
	if (outputType === 'font-weight') {
		if (
			!outputRange.every(
				(output) => typeof output === 'number' || typeof output === 'string',
			)
		) {
			throw new TypeError(
				'Font weight outputRange must contain only numbers or strings',
			);
		}

View on GitHub (pinned to 46a3a6bf13)