remotion-dev/remotion · error · Error

Expected box size of ${bytesRemaining}, got ${boxSize}

Error message

Expected box size of ${bytesRemaining}, got ${boxSize}

What it means

Thrown when a sample-entry box declares a size larger than the bytes remaining in the buffer. The parser reads boxSize via getUint32 and compares to iterator.bytesRemaining(); a boxSize greater than what is left indicates truncation, corruption, or a parser that has already over-consumed earlier bytes.

Source

Thrown at packages/media-parser/src/containers/iso-base-media/stsd/samples.ts:140

	'ac-3',
	'Opus',
];

export const processIsoFormatBox = async ({
	iterator,
	logLevel,
	contentLength,
}: {
	iterator: BufferIterator;
	logLevel: MediaParserLogLevel;
	contentLength: number;
}): Promise<FormatBoxAndNext> => {
	const fileOffset = iterator.counter.getOffset();
	const bytesRemaining = iterator.bytesRemaining();
	const boxSize = iterator.getUint32();

	if (bytesRemaining < boxSize) {
		throw new Error(`Expected box size of ${bytesRemaining}, got ${boxSize}`);
	}

	const boxFormat = iterator.getAtom();

	const isVideo = videoTags.includes(boxFormat);
	const isAudio =
		audioTags.includes(boxFormat) || audioTags.includes(Number(boxFormat));

	// 6 reserved bytes
	iterator.discard(6);

	const dataReferenceIndex = iterator.getUint16();

	if (!isVideo && !isAudio) {
		const bytesRemainingInBox =
			boxSize - (iterator.counter.getOffset() - fileOffset);
		iterator.discard(bytesRemainingInBox);

View on GitHub (pinned to 78fe4bb3fd)

Solutions

1. Confirm the file is fully downloaded: compare file size on disk to the Content-Length / expected size.
2. Run `mp4box -info input.mp4` or `ffprobe` to locate the corrupt atom.
3. Re-fetch or re-encode the source so the byte stream is complete.
4. If parsing a stream incrementally, ensure you have buffered the full box (size + 8 header) before invoking parseIsoFormatBox.

Example fix

// before: parsing a partial buffer where declared size > remaining bytes
// after: wait until the full box is buffered
const fullBoxReady = iterator.bytesRemaining() >= declaredBoxSize;
if (!fullBoxReady) return needMoreData();

// Ensure the full box is buffered before parsing sample entries
const remaining = iterator.bytesRemaining();
if (remaining < declaredBoxSize) {
  // need more data; do not call parseIsoFormatBox yet
}

try {
  await parseMedia({src, fields: {dimensions: true}});
} catch (err) {
  if (err instanceof Error && err.message.startsWith('Expected box size of')) {
    // file truncated; fetch complete bytes or reject the upload
  } else throw err;
}

When it happens

Trigger: Calling parseIsoFormatBox on a truncated stream where the declared atom size exceeds available data, or after an earlier parser left the cursor past the true box boundary.

Common situations: Streaming/incomplete downloads where the moov or mdat is cut off; files served with an incorrect Content-Length; partial writes from a recorder that crashed mid-encode.

Related errors

• read too many bytes - size: ${size}, read: ${iterator.counte
• Expected remaining bytes to be 0, got ${remaining}
• expected 0 bytes ${bytesRemaining}
• Expected stsz box in trak box
• Expected stco box in trak box

AI-assisted analysis of remotion-dev/remotion@78fe4bb3fd (2026-08-12). Data as JSON: /api/errors/6c30b42e6a1acf21. Report an issue: GitHub.