remotion-dev/remotion · error · Error

The "${nameOfProp}" prop ${location} must be a number, but y

Error message

The "${nameOfProp}" prop ${location} must be a number, but you passed a value of type ${typeof amount}

What it means

`validateDimension` checks the `width`/`height` of a composition (whether declared on `<Composition>` or returned from `calculateMetadata`). The first check requires a `number` type; any non-number — including `undefined` (which happens when neither the prop nor calculated metadata supplies a dimension) — throws.

Source

Thrown at packages/core/src/validation/validate-dimensions.ts:7

export function validateDimension(
	amount: unknown,
	nameOfProp: string,
	location: string,
): asserts amount is number {
	if (typeof amount !== 'number') {
		throw new Error(
			`The "${nameOfProp}" prop ${location} must be a number, but you passed a value of type ${typeof amount}`,
		);
	}

	if (isNaN(amount)) {
		throw new TypeError(
			`The "${nameOfProp}" prop ${location} must not be NaN, but is NaN.`,
		);
	}

	if (!Number.isFinite(amount)) {
		throw new TypeError(
			`The "${nameOfProp}" prop ${location} must be finite, but is ${amount}.`,
		);
	}

	if (amount % 1 !== 0) {
		throw new TypeError(

View on GitHub (pinned to 78fe4bb3fd)

Solutions

Provide numeric `width`/`height` on `<Composition>`, or ensure `calculateMetadata` returns them.
Coerce string sources: `Number(config.width)`.
Never rely on implicit conversion — strings are not accepted.

Example fix

// before
<Composition width="1920" height="1080" ... />
// after
<Composition width={1920} height={1080} ... />

Defensive patterns

Strategy: type-guard

Validate before calling

if (typeof w !== 'number') {
  throw new Error('width must be a number, got ' + typeof w);
}

Type guard

const isDimension = (v) => typeof v === 'number' && !Number.isNaN(v);

Prevention

Always pass numeric literals for width/height.
Coerce config/env dimensions with Number() and validate.
Ensure calculateMetadata always returns width and height.

When it happens

Trigger: Setting `width`/`height` to a string (`'1920'`), or leaving both the `<Composition>` prop and the `calculateMetadata` return value unset so that `undefined` reaches the validator.

Common situations: Reading dimensions from URL params, env vars, or a JSON config as strings without coercing; forgetting width/height on a composition that relies on `calculateMetadata` which fails to return them; SSR where metadata resolution returns nothing.

Related errors

AI-assisted analysis of remotion-dev/remotion@78fe4bb3fd (2026-08-12). Data as JSON: /api/errors/6456fae2450d784d. Report an issue: GitHub.