What causes "Expected track type segment" in remotion-dev/remotion?

Re-mux with a conformant tool: `ffmpeg -i in.webm -c copy out.webm` (ffmpeg rewrites well-formed headers).

remotion-dev/remotion · error · Error

Expected track type segment

Error message

Expected track type segment

What it means

Thrown by `getTrack` (make-track.ts:273) when `getTrackTypeSegment(track)` returns null — the TrackEntry has no `TrackType` child element. TrackType (video/audio/subtitle/etc.) is mandatory in Matroska and is the first thing `getTrack` reads to dispatch, so its absence prevents any track classification.

Source

Thrown at packages/media-parser/src/containers/webm/make-track.ts:273

	if (codec.value === 'A_MPEG/L3') {
		return 'mp3';
	}

	throw new Error(`Unknown codec: ${codec.value}`);
};

export const getTrack = ({
	timescale,
	track,
}: {
	timescale: number;
	track: TrackEntry;
}): MediaParserVideoTrack | MediaParserAudioTrack | null => {
	const trackType = getTrackTypeSegment(track);

	if (!trackType) {
		throw new Error('Expected track type segment');
	}

	const trackId = getTrackId(track);

	if (trackTypeToString(trackType.value.value) === 'video') {
		const width = getWidthSegment(track);

		if (width === null) {
			throw new Error('Expected width segment');
		}

		const height = getHeightSegment(track);

		if (height === null) {
			throw new Error('Expected height segment');
		}

		const displayHeight = getDisplayHeightSegment(track);

View on GitHub (pinned to 78fe4bb3fd)

Solutions

Re-mux with a conformant tool: `ffmpeg -i in.webm -c copy out.webm` (ffmpeg rewrites well-formed headers).
Verify the file opens in ffprobe/VLC; if not, the source is corrupt.
Re-download or re-encode from the original source.
Catch and reject the asset upstream.

Defensive patterns

Strategy: try-catch

Validate before calling

// Confirm the file is well-formed before parsing.
import { execFile } from 'node:child_process';
import { promisify } from 'node:util';
const exec = promisify(execFile);
async function isWellFormed(filePath) {
  try {
    await exec('ffprobe', ['-v', 'error', filePath]);
    return true;
  } catch {
    return false;
  }
}

Try / catch

try {
  await parseMedia({ src, fields: { tracks: true } });
} catch (err) {
  if (err instanceof Error && err.message === 'Expected track type segment') {
    console.warn('TrackEntry missing TrackType — malformed file:', src);
    return null;
  }
  throw err;
}

Prevention

Run ffprobe on untrusted media before parseMedia to catch malformed headers.
Re-mux corrupt files with ffmpeg so required EBML elements are written.
Reject malformed assets at upload rather than crashing during parse.

When it happens

Trigger: A TrackEntry element that lacks the `TrackType` child. Caused by truncated/corrupt EBML, non-conformant muxers, or parser mis-segmentation of the Tracks box.

Common situations: Corrupt or partially written MKV/WebM headers; files from experimental muxers; truncated downloads where the Tracks box is incomplete. Rare for files that play correctly anywhere.

Related errors

AI-assisted analysis of remotion-dev/remotion@78fe4bb3fd (2026-08-12). Data as JSON: /api/errors/293f3f784db7735f. Report an issue: GitHub.