Bump minor version

dev/convert.html

@@ -4,7 +4,7 @@
 <script src="../packages/mp3-encoder/dist/bundles/mediabunny-mp3-encoder.js"></script>
 
 <script type="module">
-	MediabunnyMp3Encoder.registerMp3Encoder();
+	//MediabunnyMp3Encoder.registerMp3Encoder();
 
 	const fileInput = document.createElement('input');
 	fileInput.type = 'file';
@@ -24,7 +24,7 @@
 			chunked: true,
 			chunkSize: 2**20
 		});
-		const outputFormat = new Mediabunny.Mp3OutputFormat({});
+		const outputFormat = new Mediabunny.Mp4OutputFormat({});
 
 		const button = document.createElement('button');
 		button.textContent = 'Cancel';
@@ -92,6 +92,9 @@
 			},
 			*/
 			video: () => ({
+				width: 300,
+				//alpha: 'keep',
+				//width: 320,
 				//discard: true,
 				//discard: true,
 				//crop: {
@@ -126,7 +129,7 @@
 				//width: 200,
 				//height: 100,
 			}),
-			tags: {
+			tags: {} ?? {
 				title: 'Bigggy',
 				artist: 'Buck Bunny',
 				images: [{
@@ -144,8 +147,8 @@
 				}
 			},
 			trim: {
-				//start: 10,
+				start: 0,
-				//end: 20
+				end: 10
 			},
 		});
 		console.log(conversion);

docs/guide/converting-media-files.md

@@ -13,6 +13,7 @@ It has the following features:
 - Video rotation
 - Video cropping
 - Video frame rate adjustment
+- Video transparency removal/preservation
 - Audio resampling
 - Audio up/downmixing
 
@@ -41,6 +42,14 @@ const output = new Output({
 });
 
 const conversion = await Conversion.init({ input, output });
+if (!conversion.isValid) {
+	// Conversion is invalid and cannot be executed without error.
+	// This field gives reasons for why tracks were discarded:
+	conversion.discardedTracks; // => DiscardedTrack[]
+
+	return;
+}
+
 await conversion.execute();
 
 // output.target.buffer contains the final file
@@ -57,7 +66,7 @@ Unconfigured, the conversion process handles all the details automatically, such
 - Copying media data whenever possible, otherwise transcoding it
 - Dropping tracks that aren't supported in the output format
 
-You should consider inspecting the [discarded tracks](#discarded-tracks) before executing a `Conversion`.
+You should consider inspecting `isValid` and the [discarded tracks](#discarded-tracks) before executing a `Conversion`.
 
 ### Monitoring progress
 
@@ -114,6 +123,7 @@ type ConversionVideoOptions = {
 	frameRate?: number;
 	codec?: VideoCodec;
 	bitrate?: number | Quality;
+	alpha?: 'discard' | 'keep'; // Defaults to 'discard'
 	forceTranscode?: boolean;
 };
 ```
@@ -352,6 +362,8 @@ type DiscardedTrack = {
 
 Since you can inspect this list before executing a `Conversion`, this gives you the option to decide if you still want to move forward with the conversion process.
 
+If `isValid` is `false`, then the discarded tracks caused the `Conversion` to become invalid. For example, this can happen when a format requires a specific codec but that codec cannot be encoded.
+
 ---
 
 The following reasons exist:

docs/guide/quick-start.md

@@ -419,7 +419,7 @@ const context = canvas.getContext('2d', { alpha: true })!;
 
 const source = new CanvasSource(canvas, {
 	codec: 'vp9',
-	quality: QUALITY_MEDIUM,
+	bitrate: QUALITY_MEDIUM,
 	alpha: 'keep', // => Also encode alpha data
 });
 output.addVideoTrack(source);
@@ -484,7 +484,14 @@ const output = new Output({
 });
 
 const conversion = await Conversion.init({ input, output });
-conversion.discardedTracks; // List of tracks that won't make it into the output
+if (!conversion.isValid) {
+	// The conversion isn't possible and would error upon execution.
+	// Check `discardedTracks` for the reasons.
+	return;
+}
+
+// List of tracks that won't make it into the output:
+conversion.discardedTracks;
 
 conversion.onProgress = (progress) => {
 	progress; // Number between 0 and 1, inclusive

package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "mediabunny",
-  "version": "1.20.0",
+  "version": "1.21.0",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "mediabunny",
-      "version": "1.20.0",
+      "version": "1.21.0",
       "license": "MPL-2.0",
       "workspaces": [
         "packages/*"
@@ -7749,9 +7749,9 @@
       }
     },
     "node_modules/mediabunny": {
-      "version": "1.19.1",
+      "version": "1.20.1",
-      "resolved": "https://registry.npmjs.org/mediabunny/-/mediabunny-1.19.1.tgz",
+      "resolved": "https://registry.npmjs.org/mediabunny/-/mediabunny-1.20.1.tgz",
-      "integrity": "sha512-nyaxskRhj7w634RZ/D0+xbc//nclDVBM1eG9hrrPL/lEG4PW1pBSRHsgPRXQX/PvUXNfJTYQsTl0SYFCrch9PA==",
+      "integrity": "sha512-p5vwGxXFQ+c0fvLph/VlHpntnOw6jGeWXDDNhtSHuVOOt6A346BhX8qLOuN05uWSav5x7PpIM1pjhtSIGC/fyw==",
       "license": "MPL-2.0",
       "peer": true,
       "workspaces": [
@@ -12242,7 +12242,7 @@
     },
     "packages/mp3-encoder": {
       "name": "@mediabunny/mp3-encoder",
-      "version": "1.20.0",
+      "version": "1.21.0",
       "license": "MPL-2.0",
       "devDependencies": {
         "@types/emscripten": "^1.40.1"

package.json

@@ -1,7 +1,7 @@
 {
   "name": "mediabunny",
   "author": "Vanilagy",
-  "version": "1.20.0",
+  "version": "1.21.0",
   "description": "Pure TypeScript media toolkit for reading, writing, and converting media files, directly in the browser.",
   "type": "module",
   "workspaces": [

packages/mp3-encoder/package.json

@@ -1,7 +1,7 @@
 {
   "name": "@mediabunny/mp3-encoder",
   "author": "Vanilagy",
-  "version": "1.20.0",
+  "version": "1.21.0",
   "description": "MP3 encoder extension for Mediabunny, based on LAME.",
   "main": "./dist/bundles/mediabunny-mp3-encoder.mjs",
   "module": "./dist/bundles/mediabunny-mp3-encoder.mjs",

src/conversion.ts

@@ -96,6 +96,13 @@ export type ConversionOptions = {
 	 * If no function is set, the input's metadata tags will be copied to the output.
 	 */
 	tags?: MetadataTags | ((inputTags: MetadataTags) => MaybePromise<MetadataTags>);
+
+	/**
+	 * Whether to show potential console warnings about discarded tracks after calling `Conversion.init()`, defaults to
+	 * `true`. Set this to `false` if you're properly handling the `discardedTracks` and `isValid` fields already and
+	 * want to keep the console output clean.
+	 */
+	showWarnings?: boolean;
 };
 
 /**
@@ -153,6 +160,12 @@ export type ConversionVideoOptions = {
 	codec?: VideoCodec;
 	/** The desired bitrate of the output video. */
 	bitrate?: number | Quality;
+	/**
+	 * Whether to discard or keep the transparency information of the input video. The default is `'discard'`. Note that
+	 * for `'keep'` to produce a transparent video, you must use an output config that supports it, such as WebM with
+	 * VP9.
+	 */
+	alpha?: 'discard' | 'keep';
 	/** When `true`, video will always be re-encoded instead of directly copying over the encoded samples. */
 	forceTranscode?: boolean;
 };
@@ -212,7 +225,7 @@ const validateVideoOptions = (videoOptions: ConversionVideoOptions | undefined)
 		throw new TypeError('options.video.height, when provided, must be a positive integer.');
 	}
 	if (videoOptions?.fit !== undefined && !['fill', 'contain', 'cover'].includes(videoOptions.fit)) {
-		throw new TypeError('options.video.fit, when provided, must be one of "fill", "contain", or "cover".');
+		throw new TypeError('options.video.fit, when provided, must be one of \'fill\', \'contain\', or \'cover\'.');
 	}
 	if (
 		videoOptions?.width !== undefined
@@ -236,6 +249,9 @@ const validateVideoOptions = (videoOptions: ConversionVideoOptions | undefined)
 	) {
 		throw new TypeError('options.video.frameRate, when provided, must be a finite positive number.');
 	}
+	if (videoOptions?.alpha !== undefined && !['discard', 'keep'].includes(videoOptions.alpha)) {
+		throw new TypeError('options.video.alpha, when provided, must be either \'discard\' or \'keep\'.');
+	}
 };
 
 const validateAudioOptions = (audioOptions: ConversionAudioOptions | undefined) => {
@@ -371,6 +387,11 @@ export class Conversion {
 	/** @internal */
 	_lastProgress = 0;
 
+	/**
+	 * Whether this conversion, as it has been configured, is valid and can be executed. If this field is `false`, check
+	 * the `discardedTracks` field for reasons.
+	 */
+	isValid = false;
 	/** The list of tracks that are included in the output file. */
 	readonly utilizedTracks: InputTrack[] = [];
 	/** The list of tracks from the input file that have been discarded, alongside the discard reason. */
@@ -440,6 +461,9 @@ export class Conversion {
 		if (typeof options.tags === 'object') {
 			validateMetadataTags(options.tags);
 		}
+		if (options.showWarnings !== undefined && typeof options.showWarnings !== 'boolean') {
+			throw new TypeError('options.showWarnings, when provided, must be a boolean.');
+		}
 
 		this._options = options;
 		this.input = options.input;
@@ -518,12 +542,6 @@ export class Conversion {
 			}
 		}
 
-		const unintentionallyDiscardedTracks = this.discardedTracks.filter(x => x.reason !== 'discarded_by_user');
-		if (unintentionallyDiscardedTracks.length > 0) {
-			// Let's give the user a notice/warning about discarded tracks so they aren't confused
-			console.warn('Some tracks had to be discarded from the conversion:', unintentionallyDiscardedTracks);
-		}
-
 		// Now, let's deal with metadata tags
 
 		const inputTags = await this.input.getMetadataTags();
@@ -551,14 +569,105 @@ export class Conversion {
 		}
 
 		this.output.setMetadataTags(outputTags);
+
+		// Let's check if the conversion can actually be executed
+		this.isValid = this._totalTrackCount >= outputTrackCounts.total.min
+			&& this._addedCounts.video >= outputTrackCounts.video.min
+			&& this._addedCounts.audio >= outputTrackCounts.audio.min
+			&& this._addedCounts.subtitle >= outputTrackCounts.subtitle.min;
+
+		if (this._options.showWarnings ?? true) {
+			const warnElements: unknown[] = [];
+
+			const unintentionallyDiscardedTracks = this.discardedTracks.filter(x => x.reason !== 'discarded_by_user');
+			if (unintentionallyDiscardedTracks.length > 0) {
+				// Let's give the user a notice/warning about discarded tracks so they aren't confused
+				warnElements.push(
+					'Some tracks had to be discarded from the conversion:', unintentionallyDiscardedTracks,
+				);
+			}
+
+			if (!this.isValid) {
+				warnElements.push('\n\n' + this._getInvalidityExplanation().join(''));
+			}
+
+			if (warnElements.length > 0) {
+				console.warn(...warnElements);
+			}
+		}
 	}
 
-	/** Executes the conversion process. Resolves once conversion is complete. */
+	/** @internal */
+	_getInvalidityExplanation() {
+		const elements: string[] = [];
+
+		if (this.discardedTracks.length === 0) {
+			elements.push(
+				'Due to missing tracks, this conversion cannot be executed.',
+			);
+		} else {
+			const encodabilityIsTheProblem = this.discardedTracks.every(x =>
+				x.reason === 'discarded_by_user' || x.reason === 'no_encodable_target_codec',
+			);
+
+			elements.push(
+				'Due to discarded tracks, this conversion cannot be executed.',
+			);
+
+			if (encodabilityIsTheProblem) {
+				const codecs = this.discardedTracks.flatMap((x) => {
+					if (x.reason === 'discarded_by_user') return [];
+
+					if (x.track.type === 'video') {
+						return this.output.format.getSupportedVideoCodecs();
+					} else if (x.track.type === 'audio') {
+						return this.output.format.getSupportedAudioCodecs();
+					} else {
+						return this.output.format.getSupportedSubtitleCodecs();
+					}
+				});
+
+				if (codecs.length === 1) {
+					elements.push(
+						`\nTracks were discarded because your environment is not able to encode '${codecs[0]}'.`,
+					);
+				} else {
+					elements.push(
+						'\nTracks were discarded because your environment is not able to encode any of the following'
+						+ ` codecs: ${codecs.map(x => `'${x}'`).join(', ')}.`,
+					);
+				}
+
+				if (codecs.includes('mp3')) {
+					elements.push(
+						`\nThe @mediabunny/mp3-encoder extension package provides support for encoding MP3.`,
+					);
+				}
+			} else {
+				elements.push('\nCheck the discardedTracks field for more info.');
+			}
+		}
+
+		return elements;
+	}
+
+	/**
+	 * Executes the conversion process. Resolves once conversion is complete.
+	 *
+	 * Will throw if `isValid` is `false`.
+	 */
 	async execute() {
+		if (!this.isValid) {
+			throw new Error(
+				'Cannot execute this conversion because its output configuration is invalid. Make sure to always check'
+				+ ' the isValid field before executing a conversion.\n'
+				+ this._getInvalidityExplanation().join(''),
+			);
+		}
+
 		if (this._executed) {
 			throw new Error('Conversion cannot be executed twice.');
 		}
-
 		this._executed = true;
 
 		if (this.onProgress) {
@@ -672,6 +781,8 @@ export class Conversion {
 			|| (totalRotation !== 0 && !outputSupportsRotation)
 			|| !!crop;
 
+		const alpha = trackOptions.alpha ?? 'discard';
+
 		let videoCodecs = this.output.format.getSupportedVideoCodecs();
 		if (
 			!needsTranscode
@@ -704,6 +815,12 @@ export class Conversion {
 						return;
 					}
 
+					if (alpha === 'discard') {
+						// Feels hacky given that the rest of the packet is readonly. But, works for now.
+						delete packet.sideData.alpha;
+						delete packet.sideData.alphaByteLength;
+					}
+
 					await source.add(packet, meta);
 					this._reportProgress(track.id, packet.timestamp + packet.duration);
 				}
@@ -742,6 +859,7 @@ export class Conversion {
 				codec: encodableCodec,
 				bitrate,
 				sizeChangeBehavior: trackOptions.fit ?? 'passThrough',
+				alpha,
 				onEncodedPacket: sample => this._reportProgress(track.id, sample.timestamp + sample.duration),
 			};
 
@@ -796,6 +914,7 @@ export class Conversion {
 						rotation: totalRotation, // Bake the rotation into the output
 						crop: trackOptions.crop,
 						poolSize: 1,
+						alpha: alpha === 'keep',
 					});
 					const iterator = sink.canvases(this._startTimestamp, this._endTimestamp);
 					const frameRate = trackOptions.frameRate;

src/isobmff/isobmff-demuxer.ts

@@ -90,19 +90,6 @@ import {
 } from '../reader';
 import { MetadataTags, RichImageData } from '../tags';
 
-// https://exiftool.org/TagNames/QuickTime.html
-const UDTA_STRING_KEYS = new Set([
-	'@day', '@mak', '@mod', '@swr', '@xyz', 'CAME', 'CNCV', 'CNFV', 'CNMN', 'FIRM', 'FOV\0', 'GoPr', 'LENS', 'PXMN',
-	'SIGM', 'SNum', 'TAGS', 'albm', 'albr', 'angl', 'auth', 'ccid', 'cdis', 'clfn', 'clid', 'clsf', 'cmid', 'cmnm',
-	'coll', 'cprt', 'cver', 'cvru', 'date', 'dscp', 'fsid', 'gnre', 'hinv', 'icnu', 'info', 'infu', 'kgtt', 'loci',
-	'lrcu', 'mcvr', 'name', 'perf', 'pmcc', 'reel', 'rtng', 'scen', 'shot', 'slno', 'thmb', 'titl', 'tnam', 'urat',
-	'uuid', 'vndr', 'yrrc', '©ART', '©TIM', '©TSC', '©TSZ', '©alb', '©arg', '©ark', '©cmt', '©cok', '©com', '©cpy',
-	'©day', '©dir', '©ed1', '©ed2', '©ed3', '©ed4', '©ed5', '©ed6', '©ed7', '©ed8', '©ed9', '©enc', '©fmt', '©fpt',
-	'©frl', '©fyw', '©gen', '©gpt', '©grl', '©grp', '©gyw', '©inf', '©isr', '©lab', '©lal', '©lyr', '©mak', '©mal',
-	'©mdl', '©mod', '©nam', '©pdk', '©phg', '©prd', '©prf', '©prk', '©prl', '©req', '©snk', '©snm', '©src', '©swf',
-	'©swk', '©swr', '©too', '©trk', '©wrt', '©xsp', '©xyz', '©ysp', '©zsp',
-]);
-
 type InternalTrack = {
 	id: number;
 	demuxer: IsobmffDemuxer;
@@ -2065,7 +2052,9 @@ export class IsobmffDemuxer extends Demuxer {
 						const startPos = slice.filePos;
 						this.metadataTags.raw ??= {};
 
-						if (UDTA_STRING_KEYS.has(boxInfo.name)) {
+						if (boxInfo.name[0] === '©') {
+							// https://mp4workshop.com/about
+							// Box name starting with © indicates "international text"
 							this.metadataTags.raw[boxInfo.name] ??= readMetadataStringShort(slice);
 						} else {
 							this.metadataTags.raw[boxInfo.name] ??= readBytes(slice, boxInfo.contentSize);

src/isobmff/isobmff-reader.ts

@@ -57,8 +57,10 @@ export const readIsomVariableInteger = (slice: FileSlice) => {
 };
 
 export const readMetadataStringShort = (slice: FileSlice) => {
-	const stringLength = readU16Be(slice);
+	let stringLength = readU16Be(slice);
 	slice.skip(2); // Language
+
+	stringLength = Math.min(stringLength, slice.remainingLength);
 	return textDecoder.decode(readBytes(slice, stringLength));
 };
 

src/reader.ts

@@ -129,6 +129,11 @@ export class FileSlice {
 		this.bufferPos = value - this.offset;
 	}
 
+	/** The number of bytes left from the current pos to the end of the slice. */
+	get remainingLength() {
+		return Math.max(this.end - this.filePos, 0);
+	}
+
 	skip(byteCount: number) {
 		this.bufferPos += byteCount;
 	}
@@ -153,7 +158,8 @@ const checkIsInRange = (slice: FileSlice, bytesToRead: number) => {
 	if (slice.filePos < slice.start || slice.filePos + bytesToRead > slice.end) {
 		throw new RangeError(
 			`Tried reading [${slice.filePos}, ${slice.filePos + bytesToRead}), but slice is`
-			+ ` [${slice.start}, ${slice.end}).`,
+			+ ` [${slice.start}, ${slice.end}). This is likely an internal error, please report it alongside the file`
+			+ ` that caused it.`,
 		);
 	}
 };

src/sample.ts

@@ -620,8 +620,8 @@ export class VideoSample implements Disposable {
 		const { sx, sy, sWidth, sHeight } = this._rotateSourceRegion(
 			options.crop?.left ?? 0,
 			options.crop?.top ?? 0,
-			options.crop?.width ?? this.codedWidth,
+			options.crop?.width ?? rotatedWidth,
-			options.crop?.height ?? this.codedHeight,
+			options.crop?.height ?? rotatedHeight,
 			rotation,
 		);
 

test/browser/transparency.test.ts

@@ -9,6 +9,7 @@ import { BufferTarget } from '../../src/target.js';
 import { CanvasSource, VideoSampleSource } from '../../src/media-source.js';
 import { canEncodeVideo, QUALITY_HIGH } from '../../src/encode.js';
 import { VideoSample } from '../../src/sample.js';
+import { Conversion } from '../../src/conversion.js';
 
 test('Can decode transparent video', async () => {
 	using input = new Input({
@@ -269,3 +270,104 @@ test('Positive encodability check with alpha', async () => {
 	const result = await canEncodeVideo('vp9', { alpha: 'keep' });
 	expect(result).toBe(true);
 });
+
+test('Can transmux transparent video, discards alpha by default', async () => {
+	using input = new Input({
+		source: new UrlSource('/transparency.webm'),
+		formats: ALL_FORMATS,
+	});
+	const output = new Output({
+		format: new WebMOutputFormat(),
+		target: new BufferTarget(),
+	});
+
+	const conversion = await Conversion.init({
+		input,
+		output,
+	});
+	await conversion.execute();
+
+	using outputInput = new Input({
+		source: new BufferSource(output.target.buffer!),
+		formats: ALL_FORMATS,
+	});
+
+	const videoTrack = (await outputInput.getPrimaryVideoTrack())!;
+	expect(await videoTrack.canBeTransparent()).toBe(false);
+
+	const sink = new VideoSampleSink(videoTrack);
+	const sample = (await sink.getSample(await videoTrack.getFirstTimestamp()))!;
+	expect(sample.hasAlpha).toBe(false);
+});
+
+test('Can transmux transparent video, can keep alpha', async () => {
+	using input = new Input({
+		source: new UrlSource('/transparency.webm'),
+		formats: ALL_FORMATS,
+	});
+	const output = new Output({
+		format: new WebMOutputFormat(),
+		target: new BufferTarget(),
+	});
+
+	const conversion = await Conversion.init({
+		input,
+		output,
+		video: {
+			alpha: 'keep',
+		},
+	});
+	await conversion.execute();
+
+	using outputInput = new Input({
+		source: new BufferSource(output.target.buffer!),
+		formats: ALL_FORMATS,
+	});
+
+	const videoTrack = (await outputInput.getPrimaryVideoTrack())!;
+	expect(await videoTrack.canBeTransparent()).toBe(true);
+
+	const sink = new VideoSampleSink(videoTrack);
+	const sample = (await sink.getSample(await videoTrack.getFirstTimestamp()))!;
+	expect(sample.format).toContain('A');
+	expect(sample.hasAlpha).toBe(true);
+});
+
+test('Can reencode transparent video, keeping alpha', async () => {
+	using input = new Input({
+		source: new UrlSource('/transparency.webm'),
+		formats: ALL_FORMATS,
+	});
+	const output = new Output({
+		format: new WebMOutputFormat(),
+		target: new BufferTarget(),
+	});
+
+	const conversion = await Conversion.init({
+		input,
+		output,
+		video: {
+			width: 320,
+			alpha: 'keep',
+		},
+		trim: {
+			start: 0,
+			end: 0.5,
+		},
+	});
+	await conversion.execute();
+
+	using outputInput = new Input({
+		source: new BufferSource(output.target.buffer!),
+		formats: ALL_FORMATS,
+	});
+
+	const videoTrack = (await outputInput.getPrimaryVideoTrack())!;
+	expect(await videoTrack.canBeTransparent()).toBe(true);
+	expect(videoTrack.displayWidth).toBe(320);
+
+	const sink = new VideoSampleSink(videoTrack);
+	const sample = (await sink.getSample(await videoTrack.getFirstTimestamp()))!;
+	expect(sample.format).toContain('A');
+	expect(sample.hasAlpha).toBe(true);
+});

test/node/metadata-tags.test.ts

@@ -147,6 +147,7 @@ test('Read and write metadata, QuickTime', async () => {
 		...songMetadata,
 		raw: {
 			'©sic': 'ko mode',
+			'cust': new Uint8Array([1, 2, 3, 4]),
 		},
 	});
 
@@ -179,11 +180,62 @@ test('Read and write metadata, QuickTime', async () => {
 
 	expect(readTags.raw!['©nam']).toBe(songMetadata.title);
 	// We don't know what the data type is, so the demuxer just returns Uint8Array
-	expect(readTags.raw!['©sic']).toEqual(new Uint8Array([
+	expect(readTags.raw!['©sic']).toBe('ko mode'); // Parsed as string because it begins with ©
-		0, 7, // String length 7
+	expect(readTags.raw!['cust']).toEqual(new Uint8Array([1, 2, 3, 4]));
-		85, 196, // Language code for 'und'
+});
-		107, 111, 32, 109, 111, 100, 101, // 'ko mode'
+
-	]));
+test('Read and write metadata, MP4 with mdta format', async () => {
+	const output = new Output({
+		format: new Mp4OutputFormat({
+			metadataFormat: 'mdta',
+		}),
+		target: new BufferTarget(),
+	});
+
+	output.setMetadataTags({
+		...songMetadata,
+		raw: {
+			'AIGC': 'yes',
+			'this key is': 'crazy long',
+			'bytes': new Uint8Array([2, 3, 4, 5]),
+		},
+	});
+
+	const dummyTrack = createDummyAudioTrack('aac', output);
+
+	await output.start();
+	await dummyTrack.addPacket();
+	await output.finalize();
+
+	using input = new Input({
+		source: new BufferSource(output.target.buffer!),
+		formats: ALL_FORMATS,
+	});
+
+	const readTags = await input.getMetadataTags();
+
+	expect(readTags.title).toBe(songMetadata.title);
+	expect(readTags.description).toBe(songMetadata.description);
+	expect(readTags.artist).toBe(songMetadata.artist);
+	expect(readTags.album).toBe(songMetadata.album);
+	expect(readTags.albumArtist).toBe(songMetadata.albumArtist);
+	expect(readTags.comment).toBe(songMetadata.comment);
+	expect(readTags.lyrics).toBe(songMetadata.lyrics);
+	expect(readTags.trackNumber).toBe(songMetadata.trackNumber);
+	expect(readTags.tracksTotal).toBe(songMetadata.tracksTotal);
+	expect(readTags.discNumber).toBeUndefined(); // Not written
+	expect(readTags.discsTotal).toBeUndefined();
+	expect(readTags.date).toEqual(readTags.date);
+	expect(readTags.images).toHaveLength(1);
+	expect(readTags.images![0]!.data).toEqual(coverArt);
+	expect(readTags.images![0]!.mimeType).toEqual('image/jpeg');
+	expect(readTags.images![0]!.kind).toEqual('coverFront');
+	expect(readTags.images![0]!.description).toBeUndefined(); // Lost in MP4
+
+	expect(readTags.raw!['title']).toBe(songMetadata.title);
+	expect(readTags.raw!['AIGC']).toBe('yes');
+	expect(readTags.raw!['this key is']).toBe('crazy long');
+	expect(readTags.raw!['bytes']).toEqual(new Uint8Array([2, 3, 4, 5]));
 });
 
 test('Read MOV metadata tags, ilst with keys', async () => {