From 8fea9671ea82d0621f0142ea632dc69f91ef2cc1 Mon Sep 17 00:00:00 2001
From: Vanilagy <1696106+Vanilagy@users.noreply.github.com>
Date: Thu, 15 Jan 2026 08:51:07 +0100
Subject: [PATCH] Fix some demuxer bugs that occurred on files by FFmpeg, fix
 packet marking logic

---
 src/mpeg-ts/mpeg-ts-demuxer.ts     | 25 +++++++++++++++++--------
 test/node/mpeg-ts-demuxing.test.ts | 21 ++++++++++++++++++++-
 2 files changed, 37 insertions(+), 9 deletions(-)

diff --git a/src/mpeg-ts/mpeg-ts-demuxer.ts b/src/mpeg-ts/mpeg-ts-demuxer.ts
index d405146..4eaba45 100644
--- a/src/mpeg-ts/mpeg-ts-demuxer.ts
+++ b/src/mpeg-ts/mpeg-ts-demuxer.ts
@@ -135,8 +135,9 @@ export class MpegTsDemuxer extends Demuxer {
 			}
 
 			let currentPos = this.packetOffset;
-
 			let programMapPid: number | null = null;
+			// Some files contain these multiple times, but we only care about their first appearance
+			let hasProgramAssociationTable = false;
 			let hasProgramMap = false;
 
 			while (true) {
@@ -148,7 +149,7 @@ export class MpegTsDemuxer extends Demuxer {
 				const BYTES_BEFORE_SECTION_LENGTH = 3;
 				const BITS_IN_CRC_32 = 32; // Duh
 
-				if (section.pid === 0) {
+				if (section.pid === 0 && !hasProgramAssociationTable) {
 					const bitstream = new Bitstream(section.payload);
 					const pointerField = bitstream.readAlignedByte();
 
@@ -175,7 +176,9 @@ export class MpegTsDemuxer extends Demuxer {
 					if (programMapPid === null) {
 						throw new Error('Program Association Table must link to a Program Map Table.');
 					}
-				} else if (section.pid === programMapPid) {
+
+					hasProgramAssociationTable = true;
+				} else if (section.pid === programMapPid && !hasProgramMap) {
 					const bitstream = new Bitstream(section.payload);
 					const pointerField = bitstream.readAlignedByte();
 
@@ -1258,8 +1261,9 @@ class MpegTsVideoTrackBacking extends MpegTsTrackBacking implements InputVideoTr
 			let remaining = context.ensureBuffered(CHUNK_SIZE);
 			if (remaining instanceof Promise) remaining = await remaining;
 
-			// Search for start codes in the current chunk
-			for (let i = 0; i < remaining; i++) {
+			const startPos = context.currentPos;
+
+			while (context.currentPos - startPos < remaining) {
 				const byte = context.readU8();
 
 				// Look for 0x00 as potential start of a start code
@@ -1281,6 +1285,7 @@ class MpegTsVideoTrackBacking extends MpegTsTrackBacking implements InputVideoTr
 						context.seekTo(packetStartPos);
 						return context.supplyPacket(packetLength, 0);
 					}
+
 					return;
 				}
 
@@ -1394,14 +1399,16 @@ class MpegTsAudioTrackBacking extends MpegTsTrackBacking implements InputAudioTr
 			let remaining = context.ensureBuffered(CHUNK_SIZE);
 			if (remaining instanceof Promise) remaining = await remaining;
 
-			for (let i = 0; i < remaining; i++) {
+			const startPos = context.currentPos;
+
+			while (context.currentPos - startPos < remaining) {
 				const byte = context.readU8();
 				if (byte !== 0xff) {
 					continue;
 				}
 
 				context.skip(-1);
-				const startPos = context.currentPos;
+				const possibleHeaderStartPos = context.currentPos;
 
 				let remaining = context.ensureBuffered(MAX_FRAME_HEADER_SIZE);
 				if (remaining instanceof Promise) remaining = await remaining;
@@ -1414,7 +1421,7 @@ class MpegTsAudioTrackBacking extends MpegTsTrackBacking implements InputAudioTr
 				const header = readAdtsFrameHeader(FileSlice.tempFromBytes(headerBytes));
 
 				if (header) {
-					context.seekTo(startPos);
+					context.seekTo(possibleHeaderStartPos);
 
 					let remaining = context.ensureBuffered(header.frameLength);
 					if (remaining instanceof Promise) remaining = await remaining;
@@ -1423,6 +1430,8 @@ class MpegTsAudioTrackBacking extends MpegTsTrackBacking implements InputAudioTr
 						remaining,
 						Math.round(SAMPLES_PER_AAC_FRAME * TIMESCALE / this.elementaryStream.info.sampleRate),
 					);
+				} else {
+					context.seekTo(possibleHeaderStartPos + 1);
 				}
 			}
 
diff --git a/test/node/mpeg-ts-demuxing.test.ts b/test/node/mpeg-ts-demuxing.test.ts
index 50c7486..aced224 100644
--- a/test/node/mpeg-ts-demuxing.test.ts
+++ b/test/node/mpeg-ts-demuxing.test.ts
@@ -1,6 +1,6 @@
 import { expect, test } from 'vitest';
 import { Input } from '../../src/input.js';
-import { FilePathSource, ReadableStreamSource } from '../../src/source.js';
+import { FilePathSource, ReadableStreamSource, UrlSource } from '../../src/source.js';
 import path from 'node:path';
 import fs from 'node:fs';
 import { Readable } from 'node:stream';
@@ -450,3 +450,22 @@ test('MPEG-TS with unknown file size (ReadableStreamSource)', async () => {
 	expect((videoTrack._backing as unknown as MpegTsTrackBacking).referencePesPackets.length)
 		.toBeGreaterThanOrEqual(10);
 });
+
+test('MPEG-TS transmuxed by FFmpeg', async () => {
+	using input = new Input({
+		source: new UrlSource('https://pub-cf9fcfcb5c0a44e9b1bb5ff890e041ae.r2.dev/trim-buck-bunny-ffmpeg.ts'),
+		formats: ALL_FORMATS,
+	});
+
+	const videoTrack = await input.getPrimaryVideoTrack();
+	assert(videoTrack);
+
+	const audioTrack = await input.getPrimaryAudioTrack();
+	assert(audioTrack);
+
+	const videoPacketStats = await videoTrack.computePacketStats();
+	const audioPacketStats = await audioTrack.computePacketStats();
+
+	expect(videoPacketStats.packetCount).toBe(121);
+	expect(audioPacketStats.packetCount).toBe(235);
+});