remotion-dev/remotion · error · Error

Expected segment

Error message

Expected segment

What it means

While inside a Cluster (state.webm.isInsideCluster returned a value), the parser indexes into the parsed Segment boxes by isInsideCluster.segment and that Segment does not exist. This is an internal state-tracking inconsistency between the cluster bookkeeping and the structure list rather than a property of the bytes.

Source

Thrown at packages/media-parser/src/containers/webm/parse-webm-header.ts:50

	if (results === null) {
		return null;
	}

	if (isInsideCluster) {
		if (maySkipVideoData({state})) {
			return makeSkip(
				Math.min(
					state.contentLength,
					isInsideCluster.size + isInsideCluster.start,
				),
			);
		}

		const segments = structure.boxes.filter((box) => box.type === 'Segment');
		const segment = segments[isInsideCluster.segment];
		if (!segment) {
			throw new Error('Expected segment');
		}

		const clusters = segment.value.find((box) => box.type === 'Cluster');
		if (!clusters) {
			throw new Error('Expected cluster');
		}

		// let's not add it to the cluster
		if (results.type !== 'Block' && results.type !== 'SimpleBlock') {
			clusters.value.push(results);
		}
	} else if (isInsideSegment) {
		const segments = structure.boxes.filter((box) => box.type === 'Segment');
		const segment = segments[isInsideSegment.index];
		if (!segment) {
			throw new Error('Expected segment');
		}

View on GitHub (pinned to 78fe4bb3fd)

Solutions

1. Re-mux the file to produce a single, well-formed Segment.
2. Avoid seeking on this file (the error is reachable via the seek path); parse linearly instead.
3. Re-encode from the original source.
4. Try Mediabunny.

try {
  await parseMedia({src: 'in.mkv', fields: {durationInSeconds: true}});
} catch (err) {
  if (err instanceof Error && err.message === 'Expected segment') {
    throw new Error('Segment/Cluster state desync; re-mux the file or parse without seeking.', {cause: err});
  }
  throw err;
}

When it happens

Trigger: A Cluster was registered with a segment index that is out of range for the structure.boxes Segment list - typically a side effect of a malformed Segment header, a seek that desynced state, or an earlier parse error that left structure.boxes incomplete.

Common situations: Damaged files where the Segment appears after a Cluster, partial reads during a seek, or files with an unusual multi-Segment layout.

Related errors

• Expected cluster
• Expected to be inside segment
• Could not find sample rate or number of channels
• Expected block segment
• Expected CuePoint

AI-assisted analysis of remotion-dev/remotion@78fe4bb3fd (2026-08-12). Data as JSON: /api/errors/5c4def0ed4ea6348. Report an issue: GitHub.