remotion-dev/remotion · error · Error

inputRange must be strictly monotonically non-decreasing but

Error message

inputRange must be strictly monotonically non-decreasing but got [${arr.join(',')}]

What it means

Thrown by checkInputRange when the array is not strictly increasing. Each element must be greater than the previous one; equal or decreasing values are rejected because they create ambiguous or inverted interpolation segments. Note: the message says 'non-decreasing' but the check (arr[index] > arr[index - 1]) enforces strictly increasing — equal values also fail.

Source

Thrown at packages/animation-utils/src/transformation-helpers/interpolate-styles/index.tsx:250

	if (arr.length < 2) {
		throw new Error('inputRange must have at least 2 elements');
	}

	for (let index = 0; index < arr.length; index++) {
		if (typeof arr[index] !== 'number') {
			throw new Error(`inputRange must contain only numbers`);
		}

		if (arr[index] === -Infinity || arr[index] === Infinity) {
			throw new Error(
				`inputRange must contain only finite numbers, but got [${arr.join(
					',',
				)}]`,
			);
		}

		if (index > 0 && !(arr[index] > arr[index - 1])) {
			throw new Error(
				`inputRange must be strictly monotonically non-decreasing but got [${arr.join(
					',',
				)}]`,
			);
		}
	}
}

function checkStylesRange(arr: readonly Style[]) {
	if (arr.length < 2) {
		throw new Error('outputStyles must have at least 2 elements');
	}

	for (const index in arr) {
		if (typeof arr[index] !== 'object') {
			throw new Error('outputStyles must contain only objects');
		}
	}

View on GitHub (pinned to 78fe4bb3fd)

Solutions

Sort the range ascending and remove duplicates before calling interpolateStyles.
Ensure each keyframe frame number is strictly greater than the previous one.
Dedupe dynamic arrays with [...new Set(arr)].sort((a, b) => a - b).

Example fix

// before
interpolateStyles(frame, [0, 10, 10, 30], [...]);

// after
interpolateStyles(frame, [0, 10, 30], [...]);

Defensive patterns

Strategy: validation

Validate before calling

const isStrictlyIncreasing = (arr: number[]): boolean =>
  arr.every((x, i) => i === 0 || x > arr[i - 1]);
if (!isStrictlyIncreasing(inputRange)) {
  // dedupe + sort
  inputRange = [...new Set(inputRange)].sort((a, b) => a - b);
}

Prevention

Sort and dedupe dynamic ranges before calling interpolateStyles.
Ensure keyframe frame numbers are strictly increasing when authoring.
Remember the check is strictly increasing, despite the 'non-decreasing' wording.

When it happens

Trigger: Passing [0, 0], [30, 10], or [0, 10, 10, 20]; duplicate frame values from two keyframes at the same frame; a reversed keyframe order.

Common situations: Two keyframes sharing the same frame number; generating a range from unsorted data; copy-paste producing duplicates; rounding that collapses two distinct frames to the same integer.

Related errors

AI-assisted analysis of remotion-dev/remotion@78fe4bb3fd (2026-08-12). Data as JSON: /api/errors/b70e49b5e838f7b6. Report an issue: GitHub.