What causes "Invalid section length" in remotion-dev/remotion?

Run the file through ffmpeg -i in.ts -c copy out.ts to rewrite clean PAT/PMT sections.

remotion-dev/remotion · error · Error

Invalid section length

Error message

Invalid section length

What it means

Thrown at parse-pat.ts:58 when the PAT section_length field (10 bits) exceeds 1021 bytes. ISO/IEC 13818-1 caps section_length at 1021 (0x3FD) for ATSC/DVB, with the maximum theoretical 10-bit value being 1023 and the bottom reserved for CRC. Values above 1021 indicate a malformed section header.

Source

Thrown at packages/media-parser/src/containers/transport-stream/parse-pat.ts:58

	iterator.stopReadingBits();

	return {
		type: 'transport-stream-pat-box',
		tableId: tableId.toString(16),
		pat: tables,
	};
};

export const parsePat = (iterator: BufferIterator): TransportStreamPATBox => {
	iterator.startReadingBits();

	const tableId = iterator.getBits(8);
	iterator.getBits(1); // syntax indicator
	iterator.getBits(1); // private bit
	iterator.getBits(4);
	const sectionLength = iterator.getBits(10);
	if (sectionLength > 1021) {
		throw new Error('Invalid section length');
	}

	iterator.stopReadingBits();

	const tables = parsePatTable(iterator, tableId);
	discardRestOfPacket(iterator);
	return tables;
};

export const parseSdt = (iterator: BufferIterator): TransportStreamSdtBox => {
	iterator.startReadingBits();
	iterator.getBits(8); // table ID
	iterator.getBits(1); // section syntax indicator
	iterator.getBits(1); // private bit
	iterator.getBits(2); // reserved
	const sectionLength = iterator.getBits(12);
	iterator.stopReadingBits();
	iterator.discard(sectionLength);

View on GitHub (pinned to 78fe4bb3fd)

Solutions

Run the file through ffmpeg -i in.ts -c copy out.ts to rewrite clean PAT/PMT sections.
Confirm with tsdiscont or dvbsnoop that the PAT section_length is within bounds.
Re-acquire the source from the original encoder/broadcaster if it is a capture.
Treat the file as unsupported and surface a user-facing error rather than retrying.

Defensive patterns

Strategy: validation

Validate before calling

// Reject oversized PAT sections upstream using ffprobe
import {execSync} from 'node:child_process';
function isValidTs(src: string): boolean {
  try { execSync(`ffprobe -v error -i "${src}" -t 1 -f null -`, {stdio: 'ignore'}); return true; } catch { return false; }
}

Try / catch

try { await parseMedia({src, fields: {dimensions: true}}); }
catch (e) { if (e instanceof Error && e.message === 'Invalid section length') { /* re-mux or reject */ } else throw e; }

Prevention

Pre-screen .ts inputs with ffprobe.
Re-mux suspect files with ffmpeg -c copy to normalize section headers.
Treat PAT/PMT validation errors as fatal rather than auto-retrying unchanged.

When it happens

Trigger: parsePat reads 1 + 1 + 1 + 4 + 10 bits and inspects sectionLength; if it is greater than 1021, parsing halts. Happens when the PAT section bytes are corrupted, when a PMT or other section is misread as a PAT, or when an 8-bit clean channel has flipped bits in the length field.

Common situations: Corrupted capture from a faulty DVB/ATSC tuner; bit-flips from a partially downloaded .ts; an encoder bug that writes the wrong section_length; packet loss where the PAT payload starts at the wrong offset.

Related errors

AI-assisted analysis of remotion-dev/remotion@78fe4bb3fd (2026-08-12). Data as JSON: /api/errors/76ea1d7ab74791ea. Report an issue: GitHub.