Use edit lists to model non-zero start timestamps for regular MP4 (fixes #336); fix MP4 PCM logic breaking down with approximate packet timestamps

dev/demux.html

@@ -17,14 +17,42 @@
 			source: new Mediabunny.BlobSource(file),
 		});
 
-		const track = await input.getPrimaryVideoTrack();
+		const track = await input.getPrimaryAudioTrack();
 		const sink = new Mediabunny.EncodedPacketSink(track);
-		const packet = await sink.getFirstKeyPacket();
 		
-		console.log(packet.data.join(', '));
+		for await (const packet of sink.packets()) {
+			console.log(packet);
+		}
 
-		const config = await track.getDecoderConfig();
-		console.log(config.description.join(', '));
+		const output = new Mediabunny.Output({
+			format: new Mediabunny.Mp4OutputFormat(),
+			target: new Mediabunny.BufferTarget(),
+		});
+
+		const conversion = await Mediabunny.Conversion.init({ input, output });
+		await conversion.execute();
+
+		return;
+
+		// Download it now
+		const blob = new Blob([output.target.buffer]);
+		const url = URL.createObjectURL(blob);
+		const a = document.createElement('a');
+		a.href = url;
+		a.download = file.name.replace(/\.\w+$/, '.mp4');
+		a.click();
+		URL.revokeObjectURL(url);
+
+		/*
+		const track = await input.getPrimaryAudioTrack();
+		const sink = new Mediabunny.EncodedPacketSink(track);
+		
+		for await (const packet of sink.packets()) {
+			console.log(packet);
+		}
+
+		console.log("Done")
+		*/
 
 		/*
 		const input = new Mediabunny.Input({

src/isobmff/isobmff-boxes.ts

@@ -174,6 +174,12 @@ const u64 = (value: number) => {
 	return [bytes[0], bytes[1], bytes[2], bytes[3], bytes[4], bytes[5], bytes[6], bytes[7]] as number[];
 };
 
+const i64 = (value: number) => {
+	view.setInt32(0, Math.floor(value / 2 ** 32), false);
+	view.setUint32(4, value, false);
+	return [bytes[0], bytes[1], bytes[2], bytes[3], bytes[4], bytes[5], bytes[6], bytes[7]] as number[];
+};
+
 const fixed_8_8 = (value: number) => {
 	view.setInt16(0, 2 ** 8 * value, false);
 	return [bytes[0], bytes[1]] as number[];
@@ -384,11 +390,14 @@ export const mvhd = (
 	creationTime: number,
 	trackDatas: IsobmffTrackData[],
 ) => {
-	const duration = intoTimescale(Math.max(
+	const duration = Math.max(
 		0,
 		...trackDatas
-			.map(x => presentationSpan(x)),
-	), GLOBAL_TIMESCALE);
+			.map(trackData => (
+				intoTimescale(presentationSpan(trackData), GLOBAL_TIMESCALE)
+				+ intoTimescale(trackData.startTimestampOffset ?? 0, GLOBAL_TIMESCALE)
+			)),
+	);
 	const nextTrackId = Math.max(0, ...trackDatas.map(x => x.track.id)) + 1;
 
 	// Conditionally use u64 if u32 isn't enough
@@ -417,7 +426,9 @@ const presentationSpan = (trackData: IsobmffTrackData) => {
 	let minTimestamp = Infinity;
 	let maxEndTimestamp = -Infinity;
 
-	for (const sample of trackData.samples) {
+	for (let i = 0; i < trackData.samples.length; i++) {
+		const sample = trackData.samples[i]!;
+
 		if (sample.timestamp < minTimestamp) {
 			minTimestamp = sample.timestamp;
 		}
@@ -440,9 +451,11 @@ const presentationSpan = (trackData: IsobmffTrackData) => {
  */
 export const trak = (trackData: IsobmffTrackData, creationTime: number) => {
 	const trackMetadata = getTrackMetadata(trackData);
+	const needsEditList = trackData.startTimestampOffset !== null && trackData.startTimestampOffset > 0;
 
 	return box('trak', undefined, [
 		tkhd(trackData, creationTime),
+		needsEditList ? edts(trackData, trackData.startTimestampOffset!) : null,
 		mdia(trackData, creationTime),
 		trackMetadata.name !== undefined
 			? box('udta', undefined, [
@@ -459,10 +472,8 @@ export const tkhd = (
 	trackData: IsobmffTrackData,
 	creationTime: number,
 ) => {
-	const durationInGlobalTimescale = intoTimescale(
-		presentationSpan(trackData),
-		GLOBAL_TIMESCALE,
-	);
+	const durationInGlobalTimescale = intoTimescale(presentationSpan(trackData), GLOBAL_TIMESCALE)
+		+ intoTimescale(trackData.startTimestampOffset ?? 0, GLOBAL_TIMESCALE);
 
 	const needsU64 = !isU32(creationTime) || !isU32(durationInGlobalTimescale);
 	const u32OrU64 = needsU64 ? u64 : u32;
@@ -497,6 +508,32 @@ export const tkhd = (
 	]);
 };
 
+/** Edit Box: Specifies edits to the track's media. */
+export const edts = (trackData: IsobmffTrackData, offset: number) => {
+	const startOffset = intoTimescale(offset, GLOBAL_TIMESCALE);
+	const mediaDuration = intoTimescale(presentationSpan(trackData), GLOBAL_TIMESCALE);
+
+	const needs64Bits = !isU32(startOffset) || !isU32(mediaDuration);
+	const u32OrU64 = needs64Bits ? u64 : u32;
+	const i32OrI64 = needs64Bits ? i64 : i32;
+
+	return box('edts', undefined, [
+		fullBox('elst', needs64Bits ? 1 : 0, 0, [
+			u32(2), // Entry count
+
+			// #1
+			u32OrU64(startOffset), // Segment duration
+			i32OrI64(-1), // Media time
+			fixed_16_16(1), // Media rate
+
+			// #2
+			u32OrU64(mediaDuration), // Segment duration
+			i32OrI64(0), // Media time
+			fixed_16_16(1), // Media rate
+		]),
+	]);
+};
+
 /** Media Box: Describes and define a track's media type and sample data. */
 export const mdia = (trackData: IsobmffTrackData, creationTime: number) => box('mdia', undefined, [
 	mdhd(trackData, creationTime),
@@ -509,6 +546,7 @@ export const mdhd = (
 	trackData: IsobmffTrackData,
 	creationTime: number,
 ) => {
+	// Since the duration represents the raw media duration, edit list offsets are not taken into account here
 	const localDuration = intoTimescale(
 		presentationSpan(trackData),
 		trackData.timescale,

src/isobmff/isobmff-muxer.ts

@@ -52,7 +52,7 @@ import {
 import { buildIsobmffMimeType } from './isobmff-misc';
 import { MAX_BOX_HEADER_SIZE, MIN_BOX_HEADER_SIZE } from './isobmff-reader';
 
-export const GLOBAL_TIMESCALE = 1000;
+export const GLOBAL_TIMESCALE = 57600; // LCM of a bunch of common frame rates (24, 25, 30, 60, 144, ...)
 const TIMESTAMP_OFFSET = 2_082_844_800; // Seconds between Jan 1 1904 and Jan 1 1970
 
 export type Sample = {
@@ -85,6 +85,7 @@ export type IsobmffTrackData = {
 	compositionTimeOffsetTable: { sampleCount: number; sampleCompositionTimeOffset: number }[];
 	lastTimescaleUnits: number | null;
 	lastSample: Sample | null;
+	startTimestampOffset: number | null;
 
 	finalizedChunks: Chunk[];
 	currentChunk: Chunk | null;
@@ -120,6 +121,7 @@ export type IsobmffTrackData = {
 		 * Some players expect this for PCM audio.
 		 */
 		requiresPcmTransformation: boolean;
+		expectedNextPcmPacketTimestamp: number | null;
 		/**
 		 * The "ADTS stripping" involves removing the ADTS header from each AAC packet. SOBMFF stores raw AAC data, not
 		 * ADTS-wrapped data.
@@ -395,7 +397,10 @@ export class IsobmffMuxer extends Muxer {
 		// The frame rate set by the user may not be an integer. Since timescale is an integer, we'll approximate the
 		// frame time (inverse of frame rate) with a rational number, then use that approximation's denominator
 		// as the timescale.
-		const timescale = computeRationalApproximation(1 / (track.metadata.frameRate ?? 57600), 1e6).denominator;
+		const timescale = computeRationalApproximation(
+			1 / (track.metadata.frameRate ?? GLOBAL_TIMESCALE),
+			1e6,
+		).denominator;
 
 		const displayAspectWidth = decoderConfig.displayAspectWidth;
 		const displayAspectHeight = decoderConfig.displayAspectHeight;
@@ -425,6 +430,7 @@ export class IsobmffMuxer extends Muxer {
 			compositionTimeOffsetTable: [],
 			lastTimescaleUnits: null,
 			lastSample: null,
+			startTimestampOffset: null,
 			finalizedChunks: [],
 			currentChunk: null,
 			compactlyCodedChunkTable: [],
@@ -494,6 +500,7 @@ export class IsobmffMuxer extends Muxer {
 				requiresPcmTransformation:
 					!this.isFragmented
 					&& (PCM_AUDIO_CODECS as readonly string[]).includes(track.source._codec),
+				expectedNextPcmPacketTimestamp: null,
 				requiresAdtsStripping,
 				firstPacket: packet,
 			},
@@ -505,6 +512,7 @@ export class IsobmffMuxer extends Muxer {
 			compositionTimeOffsetTable: [],
 			lastTimescaleUnits: null,
 			lastSample: null,
+			startTimestampOffset: null,
 			finalizedChunks: [],
 			currentChunk: null,
 			compactlyCodedChunkTable: [],
@@ -547,6 +555,7 @@ export class IsobmffMuxer extends Muxer {
 			compositionTimeOffsetTable: [],
 			lastTimescaleUnits: null,
 			lastSample: null,
+			startTimestampOffset: null,
 			finalizedChunks: [],
 			currentChunk: null,
 			compactlyCodedChunkTable: [],
@@ -629,41 +638,59 @@ export class IsobmffMuxer extends Muxer {
 				packetData = packetData.subarray(headerLength);
 			}
 
-			const timestamp = this.validateAndNormalizeTimestamp(
+			let timestamp = this.validateAndNormalizeTimestamp(
 				trackData.track,
 				packet.timestamp,
 				packet.type === 'key',
 			);
+			let duration = packet.duration;
+
+			if (trackData.info.requiresPcmTransformation) {
+				// Packets may have only approximate timestamp/duration information, but for our PCM logic, we need it
+				// to be precise. So here, we refine the values.
+
+				const pcmInfo = parsePcmCodec(
+					trackData.info.decoderConfig.codec as PcmAudioCodec,
+				);
+				const frameSize = pcmInfo.sampleSize * trackData.info.numberOfChannels;
+
+				// Compute the precise duration
+				duration = packetData.byteLength / frameSize / trackData.info.sampleRate;
+
+				if (trackData.info.expectedNextPcmPacketTimestamp !== null) {
+					const diff = timestamp - trackData.info.expectedNextPcmPacketTimestamp;
+					if (diff < 0.01) {
+						timestamp = trackData.info.expectedNextPcmPacketTimestamp;
+					} else {
+						const paddedDuration = await this.padWithSilence(
+							trackData,
+							trackData.info.expectedNextPcmPacketTimestamp,
+							diff,
+						);
+						timestamp = trackData.info.expectedNextPcmPacketTimestamp + paddedDuration;
+					}
+				}
+
+				trackData.info.expectedNextPcmPacketTimestamp = timestamp + duration;
+			}
+
 			const internalSample = this.createSampleForTrack(
 				trackData,
 				packetData,
 				timestamp,
-				packet.duration,
+				duration,
 				packet.type,
 			);
 
-			if (trackData.info.requiresPcmTransformation) {
-				await this.maybePadWithSilence(trackData, timestamp);
-			}
-
 			await this.registerSample(trackData, internalSample);
 		} finally {
 			release();
 		}
 	}
 
-	private async maybePadWithSilence(trackData: IsobmffAudioTrackData, untilTimestamp: number) {
-		// The PCM transformation assumes that all samples are contiguous. This is not something that is enforced, so
-		// we need to pad the "holes" in between samples (and before the first sample) with additional
-		// "silence samples".
-
-		const lastSample = last(trackData.samples);
-		const lastEndTimestamp = lastSample
-			? lastSample.timestamp + lastSample.duration
-			: 0;
-
-		const delta = untilTimestamp - lastEndTimestamp;
-		const deltaInTimescale = intoTimescale(delta, trackData.timescale);
+	private async padWithSilence(trackData: IsobmffAudioTrackData, timestamp: number, duration: number) {
+		const deltaInTimescale = intoTimescale(duration, trackData.timescale);
+		duration = deltaInTimescale / trackData.timescale;
 
 		if (deltaInTimescale > 0) {
 			const { sampleSize, silentValue } = parsePcmCodec(
@@ -675,12 +702,14 @@ export class IsobmffMuxer extends Muxer {
 			const paddingSample = this.createSampleForTrack(
 				trackData,
 				new Uint8Array(data.buffer),
-				lastEndTimestamp,
-				delta,
+				timestamp,
+				duration,
 				'key',
 			);
 			await this.registerSample(trackData, paddingSample);
 		}
+
+		return duration;
 	}
 
 	async addSubtitleCue(track: OutputSubtitleTrack, cue: SubtitleCue, meta?: SubtitleMetadata) {
@@ -821,6 +850,11 @@ export class IsobmffMuxer extends Muxer {
 		}
 
 		if (trackData.type === 'audio' && trackData.info.requiresPcmTransformation) {
+			if (!this.isFragmented) {
+				// The first timestamp is the lowest
+				trackData.startTimestampOffset ??= trackData.timestampProcessingQueue[0]!.timestamp;
+			}
+
 			let totalDuration = 0;
 
 			// Compute the total duration in the track timescale (which is equal to the amount of PCM audio samples)
@@ -848,6 +882,10 @@ export class IsobmffMuxer extends Muxer {
 
 		const sortedTimestamps = trackData.timestampProcessingQueue.map(x => x.timestamp).sort((a, b) => a - b);
 
+		if (!this.isFragmented) {
+			trackData.startTimestampOffset ??= sortedTimestamps[0]!;
+		}
+
 		for (let i = 0; i < trackData.timestampProcessingQueue.length; i++) {
 			const sample = trackData.timestampProcessingQueue[i]!;
 
@@ -857,12 +895,6 @@ export class IsobmffMuxer extends Muxer {
 			// model it.
 			sample.decodeTimestamp = sortedTimestamps[i]!;
 
-			if (!this.isFragmented && trackData.lastTimescaleUnits === null) {
-				// In non-fragmented files, the first decode timestamp is always zero. If the first presentation
-				// timestamp isn't zero, we'll simply use the composition time offset to achieve it.
-				sample.decodeTimestamp = 0;
-			}
-
 			const sampleCompositionTimeOffset
 				= intoTimescale(sample.timestamp - sample.decodeTimestamp, trackData.timescale);
 			const durationInTimescale = intoTimescale(sample.duration, trackData.timescale);
@@ -1377,6 +1409,17 @@ export class IsobmffMuxer extends Muxer {
 		} else {
 			for (const trackData of this.trackDatas) {
 				await this.finalizeCurrentChunk(trackData);
+
+				// Must hold because we will have processed at least one sample
+				assert(trackData.startTimestampOffset !== null);
+
+				// Shift all of the samples by the start offset. We'll then write out an edit list that will shift them
+				// back to their proper spot in the composition.
+				for (let i = 0; i < trackData.samples.length; i++) {
+					const sample = trackData.samples[i]!;
+					sample.timestamp -= trackData.startTimestampOffset;
+					sample.decodeTimestamp -= trackData.startTimestampOffset;
+				}
 			}
 		}
 

test/node/isobmff-muxer.test.ts

@@ -9,6 +9,8 @@ import { BufferTarget } from '../../src/target.js';
 import { Mp4OutputFormat } from '../../src/output-format.js';
 import { Conversion } from '../../src/conversion.js';
 import { assert } from '../../src/misc.js';
+import { EncodedAudioPacketSource, EncodedVideoPacketSource } from '../../src/media-source.js';
+import { EncodedPacket } from '../../src/packet.js';
 
 const __dirname = new URL('.', import.meta.url).pathname;
 
@@ -104,3 +106,249 @@ test('Fragmented fMP4 with video+audio preserves B-frame CTS', async () => {
 
 	expect(timestamps).toEqual(originalTimestamps);
 });
+
+test('Zero start timestamp, regular MP4', async () => {
+	const output = new Output({
+		format: new Mp4OutputFormat(),
+		target: new BufferTarget(),
+	});
+
+	const source = new EncodedVideoPacketSource('vp8');
+	output.addVideoTrack(source);
+
+	await output.start();
+
+	const meta = { decoderConfig: { codec: 'vp8', codedWidth: 1280, codedHeight: 720 } };
+
+	await source.add(new EncodedPacket(new Uint8Array(1024), 'key', 0, 0.1), meta);
+	await source.add(new EncodedPacket(new Uint8Array(1024), 'delta', 0.1, 0.1));
+	await source.add(new EncodedPacket(new Uint8Array(1024), 'delta', 0.2, 0.1));
+	await source.add(new EncodedPacket(new Uint8Array(1024), 'delta', 0.3, 0.1));
+
+	await output.finalize();
+
+	// Hacky but works
+	const str = String.fromCharCode(...new Uint8Array(output.target.buffer!));
+	expect(str.includes('edts') || str.includes('elst')).toBe(false);
+});
+
+test('Non-zero start timestamp, regular MP4', async () => {
+	const output = new Output({
+		format: new Mp4OutputFormat(),
+		target: new BufferTarget(),
+	});
+
+	const source = new EncodedVideoPacketSource('vp8');
+	output.addVideoTrack(source);
+
+	await output.start();
+
+	const meta = { decoderConfig: { codec: 'vp8', codedWidth: 1280, codedHeight: 720 } };
+
+	await source.add(new EncodedPacket(new Uint8Array(1024), 'key', 1, 0.1), meta);
+	await source.add(new EncodedPacket(new Uint8Array(1024), 'delta', 1.1, 0.1));
+	await source.add(new EncodedPacket(new Uint8Array(1024), 'delta', 1.2, 0.1));
+	await source.add(new EncodedPacket(new Uint8Array(1024), 'delta', 1.3, 0.1));
+
+	await output.finalize();
+
+	// Hacky but works
+	const str = String.fromCharCode(...new Uint8Array(output.target.buffer!));
+	expect(str.includes('edts') && str.includes('elst')).toBe(true);
+
+	using input = new Input({
+		source: new BufferSource(output.target.buffer!),
+		formats: ALL_FORMATS,
+	});
+
+	const track = await input.getPrimaryVideoTrack();
+	assert(track);
+	const sink = new EncodedPacketSink(track);
+
+	const timestamps: number[] = [];
+	const durations: number[] = [];
+	for await (const packet of sink.packets()) {
+		timestamps.push(packet.timestamp);
+		durations.push(packet.duration);
+	}
+
+	expect(timestamps).toEqual([1, 1.1, 1.2, 1.3]);
+	expect(durations).toEqual([0.1, 0.1, 0.1, 0.1]);
+});
+
+test('Non-zero start timestamp, fragmented MP4', async () => {
+	const output = new Output({
+		format: new Mp4OutputFormat({ fastStart: 'fragmented' }),
+		target: new BufferTarget(),
+	});
+
+	const source = new EncodedVideoPacketSource('vp8');
+	output.addVideoTrack(source);
+
+	await output.start();
+
+	const meta = { decoderConfig: { codec: 'vp8', codedWidth: 1280, codedHeight: 720 } };
+
+	await source.add(new EncodedPacket(new Uint8Array(1024), 'key', 1, 0.1), meta);
+	await source.add(new EncodedPacket(new Uint8Array(1024), 'delta', 1.1, 0.1));
+	await source.add(new EncodedPacket(new Uint8Array(1024), 'delta', 1.2, 0.1));
+	await source.add(new EncodedPacket(new Uint8Array(1024), 'delta', 1.3, 0.1));
+
+	await output.finalize();
+
+	// Hacky but works
+	const str = String.fromCharCode(...new Uint8Array(output.target.buffer!));
+	expect(str.includes('edts') || str.includes('elst')).toBe(false);
+
+	using input = new Input({
+		source: new BufferSource(output.target.buffer!),
+		formats: ALL_FORMATS,
+	});
+
+	const track = await input.getPrimaryVideoTrack();
+	assert(track);
+	const sink = new EncodedPacketSink(track);
+
+	const timestamps: number[] = [];
+	const durations: number[] = [];
+	for await (const packet of sink.packets()) {
+		timestamps.push(packet.timestamp);
+		durations.push(packet.duration);
+	}
+
+	expect(timestamps).toEqual([1, 1.1, 1.2, 1.3]);
+	expect(durations).toEqual([0.1, 0.1, 0.1, 0.1]);
+});
+
+test('PCM audio', async () => {
+	const output = new Output({
+		format: new Mp4OutputFormat(),
+		target: new BufferTarget(),
+	});
+
+	const source = new EncodedAudioPacketSource('pcm-s16');
+	output.addAudioTrack(source);
+
+	await output.start();
+
+	const meta = { decoderConfig: { codec: 'pcm-s16', numberOfChannels: 2, sampleRate: 48000 } };
+
+	await source.add(new EncodedPacket(new Uint8Array(1024), 'key', 0, 1024 / 2 / 2 / 48000), meta);
+
+	await output.finalize();
+
+	const input = new Input({
+		source: new BufferSource(output.target.buffer!),
+		formats: ALL_FORMATS,
+	});
+	const audioTrack = await input.getPrimaryAudioTrack();
+	assert(audioTrack);
+
+	expect(await audioTrack.getFirstTimestamp()).toBe(0);
+});
+
+test('PCM audio with non-zero timestamp', async () => {
+	const output = new Output({
+		format: new Mp4OutputFormat(),
+		target: new BufferTarget(),
+	});
+
+	const source = new EncodedAudioPacketSource('pcm-s16');
+	output.addAudioTrack(source);
+
+	await output.start();
+
+	const meta = { decoderConfig: { codec: 'pcm-s16', numberOfChannels: 2, sampleRate: 48000 } };
+
+	await source.add(new EncodedPacket(new Uint8Array(1024), 'key', 1, 1024 / 2 / 2 / 48000), meta);
+
+	await output.finalize();
+
+	const input = new Input({
+		source: new BufferSource(output.target.buffer!),
+		formats: ALL_FORMATS,
+	});
+	const audioTrack = await input.getPrimaryAudioTrack();
+	assert(audioTrack);
+
+	expect(await audioTrack.getFirstTimestamp()).toBe(1);
+});
+
+test('PCM audio, silence padding', async () => {
+	const output = new Output({
+		format: new Mp4OutputFormat(),
+		target: new BufferTarget(),
+	});
+
+	const source = new EncodedAudioPacketSource('pcm-s16');
+	output.addAudioTrack(source);
+
+	await output.start();
+
+	const meta = { decoderConfig: { codec: 'pcm-s16', numberOfChannels: 2, sampleRate: 48000 } };
+
+	await source.add(new EncodedPacket(new Uint8Array(1024), 'key', 0, 1024 / 2 / 2 / 48000), meta);
+	await source.add(new EncodedPacket(new Uint8Array(1024), 'key', 1, 1024 / 2 / 2 / 48000), meta);
+
+	await output.finalize();
+
+	const input = new Input({
+		source: new BufferSource(output.target.buffer!),
+		formats: ALL_FORMATS,
+	});
+	const audioTrack = await input.getPrimaryAudioTrack();
+	assert(audioTrack);
+
+	expect(await audioTrack.getCodec()).toBe('pcm-s16');
+	const numChannels = await audioTrack.getNumberOfChannels();
+
+	const expectedFrameCount = 48000 + 256;
+	const sink = new EncodedPacketSink(audioTrack);
+	let frameCount = 0;
+
+	for await (const packet of sink.packets()) {
+		frameCount += packet.byteLength / 2 / numChannels;
+	}
+
+	expect(frameCount).toBe(expectedFrameCount);
+});
+
+test('PCM audio, no silence padding with approximate timestamps', async () => {
+	const output = new Output({
+		format: new Mp4OutputFormat(),
+		target: new BufferTarget(),
+	});
+
+	const source = new EncodedAudioPacketSource('pcm-s16');
+	output.addAudioTrack(source);
+
+	await output.start();
+
+	const meta = { decoderConfig: { codec: 'pcm-s16', numberOfChannels: 2, sampleRate: 48000 } };
+
+	await source.add(new EncodedPacket(new Uint8Array(1024), 'key', 0, 1024 / 2 / 2 / 48000), meta);
+	// 0.006 is 256/48000 "rounded up", but it's close enough for silence padding not to kick in
+	await source.add(new EncodedPacket(new Uint8Array(1024), 'key', 0.006, 1024 / 2 / 2 / 48000), meta);
+
+	await output.finalize();
+
+	const input = new Input({
+		source: new BufferSource(output.target.buffer!),
+		formats: ALL_FORMATS,
+	});
+	const audioTrack = await input.getPrimaryAudioTrack();
+	assert(audioTrack);
+
+	expect(await audioTrack.getCodec()).toBe('pcm-s16');
+	const numChannels = await audioTrack.getNumberOfChannels();
+
+	const expectedFrameCount = 256 + 256;
+	const sink = new EncodedPacketSink(audioTrack);
+	let frameCount = 0;
+
+	for await (const packet of sink.packets()) {
+		frameCount += packet.byteLength / 2 / numChannels;
+	}
+
+	expect(frameCount).toBe(expectedFrameCount);
+});