Fix tests and elaborate on point in docs

docs/guide/converting-media-files.md

@@ -365,6 +365,8 @@ In this case, the output will be 15 seconds long.
 
 If only `start` is set, the clip will run until the end of the input file. If only `end` is set, the clip will start at the beginning of the input file.
 
+Note that when using the trimming defaults, the resulting media file will always begin at timestamp 0. If your input file has a start time offset (like is common with MPEG-TS files) and you want to retain that, use `trim: { start: 0 }` to ensure timestamps don't get shifted.
+
 ## Metadata tags
 
 By default, any [descriptive metadata tags](../api/MetadataTags.md) of the input will be copied to the output. If you want to further control the metadata tags written to the output, you can use the `tags` options:

test/browser/mpeg-ts-muxing.test.ts

@@ -239,7 +239,6 @@ test('MPEG-TS muxing with HEVC and MP3', async () => {
 	let isFirstVideo = true;
 	let videoPacketCountWritten = 0;
 	for await (const packet of hevcSink.packets()) {
-		console.log(packet.timestamp);
 		if (packet.timestamp >= duration) break;
 
 		await videoSource.add(packet, {
@@ -620,7 +619,11 @@ test('MPEG-TS transmux (Annex B and ADTS passthrough)', async () => {
 		target: new BufferTarget(),
 	});
 
-	const conversion = await Conversion.init({ input, output });
+	const conversion = await Conversion.init({
+		input,
+		output,
+		trim: { start: 0 }, // So we maintain the timestamps
+	});
 	expect(conversion.isValid).toBe(true);
 
 	await conversion.execute();

test/node/mpeg-ts-demuxing.test.ts

@@ -482,7 +482,7 @@ test('MPEG-TS with unknown file size (ReadableStreamSource)', async () => {
 		.toBeGreaterThanOrEqual(10);
 });
 
-test('MPEG-TS transmuxed by FFmpeg', async () => {
+test('MPEG-TS transmuxed by FFmpeg', { timeout: 30_000 }, async () => {
 	using input = new Input({
 		source: new UrlSource('https://pub-cf9fcfcb5c0a44e9b1bb5ff890e041ae.r2.dev/trim-buck-bunny-ffmpeg.ts'),
 		formats: ALL_FORMATS,