remotion-dev/remotion · warning · Error

Invalid trun number size

Error message

Invalid trun number size

What it means

Thrown in readTrunNumber() while parsing a tfra box. Same mechanism as the traf-number check: the 2-bit lengthSizeOfTrunNum field maps to a uint width other than {8,16,32,64} (i.e. 24- or 48-bit), which is not supported, so the trun number size is invalid and parsing aborts.

Source

Thrown at packages/media-parser/src/containers/iso-base-media/mfra/tfra.ts:63

): number => {
	const uintTypeTrunNum = (lengthSizeOfTrunNum + 1) * 8;
	if (uintTypeTrunNum === 8) {
		return iterator.getUint8();
	}

	if (uintTypeTrunNum === 16) {
		return iterator.getUint16();
	}

	if (uintTypeTrunNum === 32) {
		return iterator.getUint32();
	}

	if (uintTypeTrunNum === 64) {
		return Number(iterator.getUint64());
	}

	throw new Error('Invalid trun number size');
};

const readSampleNumber = (
	iterator: BufferIterator,
	lengthSizeOfSampleNum: number,
): number => {
	const uintTypeSampleNum = (lengthSizeOfSampleNum + 1) * 8;
	if (uintTypeSampleNum === 8) {
		return iterator.getUint8();
	}

	if (uintTypeSampleNum === 16) {
		return iterator.getUint16();
	}

	if (uintTypeSampleNum === 32) {
		return iterator.getUint32();
	}

View on GitHub (pinned to 78fe4bb3fd)

Solutions

1. Re-mux the fragmented file: ffmpeg -i in.mp4 -c copy -movflags +faststart out.mp4.
2. Re-fetch a clean copy of the segment.
3. Avoid the mfra path by requesting only metadata/fields that do not force full sample iteration.
4. Migrate to @remotion/mediabunny (parseMedia is deprecated).

Example fix

// before
await parseMedia({src: fragmentedMp4, reader: nodeReader});

// after
try {
  await parseMedia({src: fragmentedMp4, reader: nodeReader});
} catch (err) {
  if (err instanceof Error && /Invalid trun number size/.test(err.message)) {
    // tfra trun-number size corrupt; re-mux the fragmented file
  } else throw err;
}

// Validate the fragmented segment before parsing:
//   ffprobe -v warning in.mp4
import {execFileSync} from 'node:child_process';
function fragmentLooksIntact(file: string): boolean {
  try {
    execFileSync('ffprobe', ['-v','warning','-hide_banner', file], {encoding:'utf8', stdio:'pipe'});
    return true;
  } catch { return false; }
}

// tfra trun-number size bits are deep binary fields; not caller-type-guardable.
// => typeGuard: null

try {
  await parseMedia({src: fragmentedMp4, reader: nodeReader});
} catch (err) {
  if (err instanceof Error && /Invalid trun number size/.test(err.message)) {
    // tfra trun-number size corrupt; re-mux the fragmented file
  } else {
    throw err;
  }
}

When it happens

Trigger: parseMedia({src}) on a fragmented MP4 whose tfra box has a corrupt trun-number size field in its size-encoding byte. Only encountered when an mfra box is present (fragmented MP4 seeking index).

Common situations: Corrupted CMAF/DASH fragmented MP4 segments with an mfra index; malformed packager output; bit corruption in the tfra size byte.

Related errors

• Invalid traf number size
• Invalid sample number size
• No video section defined
• 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/44958c46b4ee62d1. Report an issue: GitHub.