remotion-dev/remotion · error

Blocking bit should be set

Error message

Blocking bit should be set

What it means

Thrown by parseFlacFrame() when, after the sync-code parsing branches, getBlockingBitStrategy() still returns undefined. The sync-code branch for blockingBit===undefined sets the strategy via setBlockingBitStrategy(); the other two branches (blockingBit===0 or 1) only validate and rely on the pre-existing strategy. Logically this throw is unreachable: if blockingBit was undefined, the strategy gets set; if it was 0 or 1, it is already defined. The check is defensive against an internal state-management bug.

Source

Thrown at packages/media-parser/src/containers/flac/parse-flac-frame.ts:183

			throw new Error('Invalid sync code');
		}

		state.flac.setBlockingBitStrategy(iterator.getBits(1));
	} else if (blockingBit === 1) {
		const bits = iterator.getBits(16);
		if (bits !== 0b1111111111111001) {
			throw new Error('Blocking bit changed, it should not');
		}
	} else if (blockingBit === 0) {
		const bits = iterator.getBits(16);
		if (bits !== 0b1111111111111000) {
			throw new Error('Blocking bit changed, it should not');
		}
	}

	const setBlockingBit = state.flac.getBlockingBitStrategy();
	if (setBlockingBit === undefined) {
		throw new Error('Blocking bit should be set');
	}

	iterator.stopReadingBits();

	const structure = state.structure.getFlacStructure();

	const minimumFrameSize =
		structure.boxes.find((b) => b.type === 'flac-streaminfo')
			?.minimumFrameSize ?? null;
	if (minimumFrameSize === null) {
		throw new Error('Expected flac-streaminfo');
	}

	if (minimumFrameSize !== 0) {
		iterator.getSlice(minimumFrameSize - 2);
	}

	while (true) {

View on GitHub (pinned to 78fe4bb3fd)

Solutions

1. If you encounter this, report it as an internal bug to the Remotion team.
2. Update to the latest @remotion/media-parser version.
3. Switch to Mediabunny (https://www.remotion.dev/docs/mediabunny/metadata).

try {
  const result = await parseMedia({src, fields: {durationInSeconds: true}});
} catch (e) {
  if (e instanceof Error && e.message === 'Blocking bit should be set') {
    // Effectively unreachable; if hit, report as internal bug
    console.error('Internal parser error: FLAC blocking-bit state not set. Report this to Remotion.');
  } else {
    throw e;
  }
}

When it happens

Trigger: Logically unreachable: the blocking-bit strategy is either already set (when blockingBit is 0 or 1) or gets set in the undefined branch. Would only fire if setBlockingBitStrategy() failed to update state, or if the control flow were modified to skip the set call.

Common situations: Should never occur in normal operation. If seen, it indicates an internal state-management bug in the FLAC parser's blocking-bit tracking or an unintended code edit.

Related errors

• Invalid block size
• Invalid channel count: ${bits.toString(2)}
• Invalid sample rate mode: ${mode.toString(2)}
• Blocking bit changed, it should not
• Streaminfo not found

AI-assisted analysis of remotion-dev/remotion@78fe4bb3fd (2026-08-12). Data as JSON: /api/errors/610104e1e164577c. Report an issue: GitHub.