remotion-dev/remotion · warning · Error

Invalid traf number size

Error message

Invalid traf number size

What it means

Thrown in readTrafNumber() while parsing a tfra (track fragment random access) box inside mfra. The 2-bit lengthSizeOfTrafNum field yields a uint width other than {8,16,32,64} bits — i.e. it maps to the unsupported 24-bit or 48-bit widths ((lengthSizeOfTrafNum+1)*8 must be one of those four). The traf number size is therefore invalid and the parser aborts.

Source

Thrown at packages/media-parser/src/containers/iso-base-media/mfra/tfra.ts:39

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

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

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

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

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

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

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

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

View on GitHub (pinned to 78fe4bb3fd)

Solutions

1. Re-mux the fragmented stream without an mfra index, or regenerate it: ffmpeg -i in.mp4 -c copy -movflags +faststart out.mp4.
2. Obtain a fresh copy of the segment if you suspect transfer corruption.
3. If you do not need seeking, request fields/on* callbacks that let the parser skip video data (maySkipVideoData path) so the mfra is not required.
4. Migrate to @remotion/mediabunny (parseMedia is deprecated).

Example fix

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

// after
try {
  const r = await parseMedia({src: fragmentedMp4, reader: nodeReader});
} catch (err) {
  if (err instanceof Error && /Invalid traf number size/.test(err.message)) {
    // mfra/tfra index corrupt; re-mux to regenerate or drop the index
  } else throw err;
}

// Only fragmented MP4 with an mfra box hits this. Validate the segment with:
//   ffprobe -v warning -show_entries format=tags 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 size-encoding bits are deep binary fields in the mfra index; not caller-type-guardable.
// => typeGuard: null

try {
  await parseMedia({src: fragmentedMp4, reader: nodeReader});
} catch (err) {
  if (err instanceof Error && /Invalid traf number size/.test(err.message)) {
    // mfra/tfra index corrupt; re-mux to regenerate or drop the index
  } else {
    throw err;
  }
}

When it happens

Trigger: parseMedia({src}) on a fragmented MP4 whose mfra/tfra box has a malformed size-encoding byte, or whose tmpByte bit-fields are corrupted. Only relevant for fragmented MP4 files that contain an mfra box (used for optimised seeking).

Common situations: Corrupted fragmented MP4 (DASH/CMAF segments with an mfra index); non-compliant packagers writing invalid tfra size fields; bit-level corruption in the tfra header.

Related errors

• Invalid trun 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/2e5543a704257452. Report an issue: GitHub.