remotion-dev/remotion · error

Expected stco box in trak box

Error message

Expected stco box in trak box

What it means

Thrown by getGroupedSamplesPositionsFromMp4 when the TrakBox has no stco (32-bit chunk-offset) box. stco gives the absolute file offset of each chunk; without it sample positions cannot be resolved, so the parser refuses rather than emit invalid offsets. Note this path does not also check for the 64-bit co64 variant.

Source

Thrown at packages/media-parser/src/get-sample-positions-from-mp4.ts:30

// example video: mehmet.mov

export const getGroupedSamplesPositionsFromMp4 = ({
	trakBox,
	bigEndian,
}: {
	trakBox: TrakBox;
	bigEndian: boolean;
}): SamplePosition[] => {
	const stscBox = getStscBox(trakBox);
	const stszBox = getStszBox(trakBox);
	const stcoBox = getStcoBox(trakBox);

	if (!stscBox) {
		throw new Error('Expected stsc box in trak box');
	}

	if (!stcoBox) {
		throw new Error('Expected stco box in trak box');
	}

	if (!stszBox) {
		throw new Error('Expected stsz box in trak box');
	}

	if (stszBox.countType !== 'fixed') {
		throw new Error('Only supporting fixed count type in stsz box');
	}

	const samples: SamplePosition[] = [];

	let timestamp = 0;

	const stscKeys = Array.from(stscBox.entries.keys());
	for (let i = 0; i < stcoBox.entries.length; i++) {
		const entry = stcoBox.entries[i];
		const chunk = i + 1;

View on GitHub (pinned to 78fe4bb3fd)

Solutions

1. Ensure the file provides stco; if the source uses co64, re-mux with ffmpeg to emit stco where possible.
2. Use a different code path that handles co64 if the library provides one, or skip this trak.
3. Wrap in try/catch and mark the trak as unsampleable when stco is absent.

Example fix

// before
const positions = getGroupedSamplesPositionsFromMp4({trakBox, bigEndian});

// after
let positions = [];
try {
  positions = getGroupedSamplesPositionsFromMp4({trakBox, bigEndian});
} catch (err) {
  console.warn('trak missing stco (or uses co64), skipping', err);
}

import {getStcoBox} from '@remotion/media-parser/containers/iso-base-media/traversal';
if (getStcoBox(trakBox)) { getGroupedSamplesPositionsFromMp4({trakBox, bigEndian}); }

const hasStco = (trak: TrakBox): boolean => getStcoBox(trak) !== null;

try { getGroupedSamplesPositionsFromMp4({trakBox, bigEndian}); } catch (e) { if (e.message === 'Expected stco box in trak box') { /* trak uses co64 or is corrupt */ } else throw e; }

When it happens

Trigger: Trak whose stbl uses co64 (64-bit offsets) instead of stco, or omits the chunk-offset box entirely. Files with non-standard sample table layouts.

Common situations: Large MP4 files (>4 GB) that use co64 rather than stco. Truncated or repaired files. Tracks muxed by tools that emit co64 exclusively.

Related errors

• Expected stsc box in trak box
• Expected stsz box in trak box
• Expected stsz box in trak box
• Expected stco box in trak box
• Expected stsc box in trak box

AI-assisted analysis of remotion-dev/remotion@78fe4bb3fd (2026-08-12). Data as JSON: /api/errors/08da37cc7183f5df. Report an issue: GitHub.