Add track-specific conversion options, fix esbuild race condition

dev/convert.html

@@ -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';
@@ -41,6 +41,7 @@
 				target
 			}),
 			audio: {
+				discard: true,
 				//codec: 'opus',
 				//bitrate: 128000,
 				//numberOfChannels: 1,
@@ -72,7 +73,7 @@
 				bitrate: 320000
 			},
 			*/
-			video: {
+			video: () => ({
 				//frameRate: 27.123,
 				//width: 320,
 				//forceTranscode: true,
@@ -91,7 +92,7 @@
 				//height: 512,
 				//width: 200,
 				//height: 100,
-			},
+			}),
 			trim: {
 				start: 0,
 				end: 20

docs/guide/converting-media-files.md

@@ -92,11 +92,9 @@ This automatically frees up all resources used by the conversion process.
 
 ## Video options
 
-You can set the `video` property in the conversion options to configure the converter's behavior for video tracks:
+You can set the `video` property in the conversion options to configure the converter's behavior for video tracks. The options are:
 ```ts
-type ConversionOptions = {
-	// ...
-	video?: {
+type ConversionVideoOptions = {
 	discard?: boolean;
 	width?: number;
 	height?: number;
@@ -107,8 +105,6 @@ type ConversionOptions = {
 	bitrate?: number | Quality;
 	forceTranscode?: boolean;
 };
-	// ...
-};
 ```
 
 For example, here we resize the video track to 720p:
@@ -125,7 +121,7 @@ const conversion = await Conversion.init({
 ```
 
 ::: info
-The provided configuration will apply equally to all video tracks of the input.
+The provided configuration will apply equally to all video tracks of the input. If you want to apply a separate configuration to each video track, check [track-specific options](#track-specific-options).
 :::
 
 ### Discarding video
@@ -143,6 +139,8 @@ The `width`, `height` and `fit` properties control how the video is resized. If
 
 If `width` or `height` is used in conjunction with `rotation`, they control the post-rotation dimensions.
 
+If you want to apply max/min constraints to a video's dimensions, check out [track-specific options](#track-specific-options).
+
 ### Adjusting frame rate
 
 The `frameRate` property can be used to set the frame rate of the output video in Hz. If not specified, the original input frame rate will be used (which may be variable).
@@ -157,11 +155,9 @@ If you want to prevent direct copying of media data and force a transcoding step
 
 ## Audio options
 
-You can set the `audio` property in the conversion options to configure the converter's behavior for audio tracks:
+You can set the `audio` property in the conversion options to configure the converter's behavior for audio tracks. The options are:
 ```ts
-type ConversionOptions = {
-	// ...
-	audio?: {
+type ConversionAudioOptions = {
 	discard?: boolean;
 	codec?: AudioCodec;
 	bitrate?: number | Quality;
@@ -169,8 +165,6 @@ type ConversionOptions = {
 	sampleRate?: number;
 	forceTranscode?: boolean;
 };
-	// ...
-};
 ```
 
 For example, here we convert the audio track to mono and set a specific sample rate:
@@ -186,7 +180,7 @@ const conversion = await Conversion.init({
 ```
 
 ::: info
-The provided configuration will apply equally to all audio tracks of the input.
+The provided configuration will apply equally to all audio tracks of the input. If you want to apply a separate configuration to each audio track, check [track-specific options](#track-specific-options).
 :::
 
 ### Discarding audio
@@ -207,6 +201,46 @@ Use the `bitrate` property to control the bitrate of the output audio. For examp
 
 If you want to prevent direct copying of media data and force a transcoding step, use `forceTranscode: true`.
 
+## Track-specific options
+
+You may want to configure your video and audio options differently depending on the specifics of the input track. Or, in case a media file has multiple video or audio tracks, you may want to discard only specific tracks or configure each track separately.
+
+For this, instead of passing an object for `video` and `audio`, you can instead pass a function:
+
+```ts
+const conversion = await Conversion.init({
+	input,
+	output,
+
+	// Function gets invoked for each video track:
+	video: (videoTrack, n) => {
+		if (n > 1) {
+			// Keep only the first video track
+			return { discard: true };
+		}
+
+		return {
+			// Shrink width to 640 only if the track is wider
+			width: Math.min(videoTrack.displayWidth, 640),
+		};
+	},
+
+	// Async functions work too:
+	audio: async (audioTrack, n) => {
+		if (audioTrack.languageCode !== 'rus') {
+			// Keep only Russian audio tracks
+			return { discard: true };
+		}
+
+		return {
+			codec: 'aac',
+		};
+	},
+});
+```
+
+For documentation about the properties of video and audio tracks, refer to [Reading track metadata](./reading-media-files#reading-track-metadata).
+
 ## Trimming
 
 Use the `trim` property in the conversion options to extract only a section of the input file into the output file:

scripts/esbuild/inlined-workers.ts

@@ -71,13 +71,18 @@ if (cacheDir === undefined) {
 	throw new Error('Cache directory not found.');
 }
 
+let i = 0;
+
 async function buildWorker(workerPath: string, extraConfig: esbuild.BuildOptions) {
 	const scriptNameParts = path.basename(workerPath).split('.');
 	scriptNameParts.pop();
+	scriptNameParts.push(String(i)); // To make sure it doesn't clash with other builds
 	scriptNameParts.push('js');
 	const scriptName = scriptNameParts.join('.');
 	const bundlePath = path.resolve(cacheDir!, scriptName);
 
+	i = (i + 1) % 32;
+
 	if (extraConfig) {
 		delete extraConfig.entryPoints;
 		delete extraConfig.outfile;

src/conversion.ts

@@ -35,22 +35,15 @@ import {
 	VideoSampleSource,
 	AudioSampleSource,
 } from './media-source';
-import { assert, clamp, normalizeRotation, promiseWithResolvers, Rotation } from './misc';
+import { assert, clamp, MaybePromise, normalizeRotation, promiseWithResolvers, Rotation } from './misc';
 import { Output, TrackType } from './output';
 import { AudioSample, VideoSample } from './sample';
 
 /**
- * The options for media file conversion.
+ * Video-specific options.
  * @public
  */
-export type ConversionOptions = {
-	/** The input file. */
-	input: Input;
-	/** The output file. */
-	output: Output;
-
-	/** Video-specific options. */
-	video?: {
+export type ConversionVideoOptions = {
 	/** If true, all video tracks will be discarded and will not be present in the output. */
 	discard?: boolean;
 	/**
@@ -90,8 +83,11 @@ export type ConversionOptions = {
 	forceTranscode?: boolean;
 };
 
-	/** Audio-specific options. */
-	audio?: {
+/**
+ * Audio-specific options.
+ * @public
+ */
+export type ConversionAudioOptions = {
 	/** If true, all audio tracks will be discarded and will not be present in the output. */
 	discard?: boolean;
 	/** The desired channel count of the output audio. */
@@ -106,6 +102,92 @@ export type ConversionOptions = {
 	forceTranscode?: boolean;
 };
 
+const validateVideoOptions = (videoOptions: ConversionVideoOptions | undefined) => {
+	if (videoOptions !== undefined && (!videoOptions || typeof videoOptions !== 'object')) {
+		throw new TypeError('options.video, when provided, must be an object.');
+	}
+	if (videoOptions?.discard !== undefined && typeof videoOptions.discard !== 'boolean') {
+		throw new TypeError('options.video.discard, when provided, must be a boolean.');
+	}
+	if (videoOptions?.forceTranscode !== undefined && typeof videoOptions.forceTranscode !== 'boolean') {
+		throw new TypeError('options.video.forceTranscode, when provided, must be a boolean.');
+	}
+	if (videoOptions?.codec !== undefined && !VIDEO_CODECS.includes(videoOptions.codec)) {
+		throw new TypeError(
+			`options.video.codec, when provided, must be one of: ${VIDEO_CODECS.join(', ')}.`,
+		);
+	}
+	if (
+		videoOptions?.bitrate !== undefined
+		&& !(videoOptions.bitrate instanceof Quality)
+		&& (!Number.isInteger(videoOptions.bitrate) || videoOptions.bitrate <= 0)
+	) {
+		throw new TypeError('options.video.bitrate, when provided, must be a positive integer or a quality.');
+	}
+	if (
+		videoOptions?.width !== undefined
+		&& (!Number.isInteger(videoOptions.width) || videoOptions.width <= 0)
+	) {
+		throw new TypeError('options.video.width, when provided, must be a positive integer.');
+	}
+	if (
+		videoOptions?.height !== undefined
+		&& (!Number.isInteger(videoOptions.height) || videoOptions.height <= 0)
+	) {
+		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".');
+	}
+	if (
+		videoOptions?.width !== undefined
+		&& videoOptions.height !== undefined
+		&& videoOptions.fit === undefined
+	) {
+		throw new TypeError(
+			'When both options.video.width and options.video.height are provided, options.video.fit must also be'
+			+ ' provided.',
+		);
+	}
+	if (videoOptions?.rotate !== undefined && ![0, 90, 180, 270].includes(videoOptions.rotate)) {
+		throw new TypeError('options.video.rotate, when provided, must be 0, 90, 180 or 270.');
+	}
+	if (
+		videoOptions?.frameRate !== undefined
+		&& (!Number.isFinite(videoOptions.frameRate) || videoOptions.frameRate <= 0)
+	) {
+		throw new TypeError('options.video.frameRate, when provided, must be a finite positive number.');
+	}
+};
+
+/**
+ * The options for media file conversion.
+ * @public
+ */
+export type ConversionOptions = {
+	/** The input file. */
+	input: Input;
+	/** The output file. */
+	output: Output;
+
+	/**
+	 * Video-specific options. When passing an object, the same options are applied to all video tracks. When passing a
+	 * function, it will be invoked for each video track and is expected to return or resolve to the options
+	 * for that specific track. The function is passed an instance of `InputVideoTrack` as well as a number `n`, which
+	 * is the 1-based index of the track in the list of all video tracks.
+	 */
+	video?: ConversionVideoOptions
+		| ((track: InputVideoTrack, n: number) => MaybePromise<ConversionVideoOptions | undefined>);
+
+	/**
+	 * Audio-specific options. When passing an object, the same options are applied to all audio tracks. When passing a
+	 * function, it will be invoked for each audio track and is expected to return or resolve to the options
+	 * for that specific track. The function is passed an instance of `InputAudioTrack` as well as a number `n`, which
+	 * is the 1-based index of the track in the list of all audio tracks.
+	 */
+	audio?: ConversionAudioOptions
+		| ((track: InputAudioTrack, n: number) => MaybePromise<ConversionAudioOptions | undefined>);
+
 	/** Options to trim the input file. */
 	trim?: {
 		/** The time in the input file in seconds at which the output file should start. Must be less than `end`.  */
@@ -115,6 +197,42 @@ export type ConversionOptions = {
 	};
 };
 
+const validateAudioOptions = (audioOptions: ConversionAudioOptions | undefined) => {
+	if (audioOptions !== undefined && (!audioOptions || typeof audioOptions !== 'object')) {
+		throw new TypeError('options.audio, when provided, must be an object.');
+	}
+	if (audioOptions?.discard !== undefined && typeof audioOptions.discard !== 'boolean') {
+		throw new TypeError('options.audio.discard, when provided, must be a boolean.');
+	}
+	if (audioOptions?.forceTranscode !== undefined && typeof audioOptions.forceTranscode !== 'boolean') {
+		throw new TypeError('options.audio.forceTranscode, when provided, must be a boolean.');
+	}
+	if (audioOptions?.codec !== undefined && !AUDIO_CODECS.includes(audioOptions.codec)) {
+		throw new TypeError(
+			`options.audio.codec, when provided, must be one of: ${AUDIO_CODECS.join(', ')}.`,
+		);
+	}
+	if (
+		audioOptions?.bitrate !== undefined
+		&& !(audioOptions.bitrate instanceof Quality)
+		&& (!Number.isInteger(audioOptions.bitrate) || audioOptions.bitrate <= 0)
+	) {
+		throw new TypeError('options.audio.bitrate, when provided, must be a positive integer or a quality.');
+	}
+	if (
+		audioOptions?.numberOfChannels !== undefined
+		&& (!Number.isInteger(audioOptions.numberOfChannels) || audioOptions.numberOfChannels <= 0)
+	) {
+		throw new TypeError('options.audio.numberOfChannels, when provided, must be a positive integer.');
+	}
+	if (
+		audioOptions?.sampleRate !== undefined
+		&& (!Number.isInteger(audioOptions.sampleRate) || audioOptions.sampleRate <= 0)
+	) {
+		throw new TypeError('options.audio.sampleRate, when provided, must be a positive integer.');
+	}
+};
+
 const FALLBACK_NUMBER_OF_CHANNELS = 2;
 const FALLBACK_SAMPLE_RATE = 48000;
 
@@ -217,94 +335,19 @@ export class Conversion {
 		if (options.output._tracks.length > 0 || options.output.state !== 'pending') {
 			throw new TypeError('options.output must be fresh: no tracks added and not started.');
 		}
-		if (options.video !== undefined && (!options.video || typeof options.video !== 'object')) {
-			throw new TypeError('options.video, when provided, must be an object.');
+
+		if (typeof options.video !== 'function') {
+			validateVideoOptions(options.video);
+		} else {
+			// We'll validate the return value later
 		}
-		if (options.video?.discard !== undefined && typeof options.video.discard !== 'boolean') {
-			throw new TypeError('options.video.discard, when provided, must be a boolean.');
-		}
-		if (options.video?.forceTranscode !== undefined && typeof options.video.forceTranscode !== 'boolean') {
-			throw new TypeError('options.video.forceTranscode, when provided, must be a boolean.');
-		}
-		if (options.video?.codec !== undefined && !VIDEO_CODECS.includes(options.video.codec)) {
-			throw new TypeError(
-				`options.video.codec, when provided, must be one of: ${VIDEO_CODECS.join(', ')}.`,
-			);
-		}
-		if (
-			options.video?.bitrate !== undefined
-			&& !(options.video.bitrate instanceof Quality)
-			&& (!Number.isInteger(options.video.bitrate) || options.video.bitrate <= 0)
-		) {
-			throw new TypeError('options.video.bitrate, when provided, must be a positive integer or a quality.');
-		}
-		if (
-			options.video?.width !== undefined
-			&& (!Number.isInteger(options.video.width) || options.video.width <= 0)
-		) {
-			throw new TypeError('options.video.width, when provided, must be a positive integer.');
-		}
-		if (
-			options.video?.height !== undefined
-			&& (!Number.isInteger(options.video.height) || options.video.height <= 0)
-		) {
-			throw new TypeError('options.video.height, when provided, must be a positive integer.');
-		}
-		if (options.video?.fit !== undefined && !['fill', 'contain', 'cover'].includes(options.video.fit)) {
-			throw new TypeError('options.video.fit, when provided, must be one of "fill", "contain", or "cover".');
-		}
-		if (
-			options.video?.width !== undefined
-			&& options.video.height !== undefined
-			&& options.video.fit === undefined
-		) {
-			throw new TypeError(
-				'When both options.video.width and options.video.height are provided, options.video.fit must also be'
-				+ ' provided.',
-			);
-		}
-		if (options.video?.rotate !== undefined && ![0, 90, 180, 270].includes(options.video.rotate)) {
-			throw new TypeError('options.video.rotate, when provided, must be 0, 90, 180 or 270.');
-		}
-		if (
-			options.video?.frameRate !== undefined
-			&& (!Number.isFinite(options.video.frameRate) || options.video.frameRate <= 0)
-		) {
-			throw new TypeError('options.video.frameRate, when provided, must be a finite positive number.');
-		}
-		if (options.audio !== undefined && (!options.audio || typeof options.audio !== 'object')) {
-			throw new TypeError('options.audio, when provided, must be an object.');
-		}
-		if (options.audio?.discard !== undefined && typeof options.audio.discard !== 'boolean') {
-			throw new TypeError('options.audio.discard, when provided, must be a boolean.');
-		}
-		if (options.audio?.forceTranscode !== undefined && typeof options.audio.forceTranscode !== 'boolean') {
-			throw new TypeError('options.audio.forceTranscode, when provided, must be a boolean.');
-		}
-		if (options.audio?.codec !== undefined && !AUDIO_CODECS.includes(options.audio.codec)) {
-			throw new TypeError(
-				`options.audio.codec, when provided, must be one of: ${AUDIO_CODECS.join(', ')}.`,
-			);
-		}
-		if (
-			options.audio?.bitrate !== undefined
-			&& !(options.audio.bitrate instanceof Quality)
-			&& (!Number.isInteger(options.audio.bitrate) || options.audio.bitrate <= 0)
-		) {
-			throw new TypeError('options.audio.bitrate, when provided, must be a positive integer or a quality.');
-		}
-		if (
-			options.audio?.numberOfChannels !== undefined
-			&& (!Number.isInteger(options.audio.numberOfChannels) || options.audio.numberOfChannels <= 0)
-		) {
-			throw new TypeError('options.audio.numberOfChannels, when provided, must be a positive integer.');
-		}
-		if (
-			options.audio?.sampleRate !== undefined
-			&& (!Number.isInteger(options.audio.sampleRate) || options.audio.sampleRate <= 0)
-		) {
-			throw new TypeError('options.audio.sampleRate, when provided, must be a positive integer.');
+
+		if (typeof options.audio !== 'function') {
+			validateAudioOptions(options.audio);
+		} else {
+			// We'll validate the return value later
 		}
+
 		if (options.trim !== undefined && (!options.trim || typeof options.trim !== 'object')) {
 			throw new TypeError('options.trim, when provided, must be an object.');
 		}
@@ -338,16 +381,36 @@ export class Conversion {
 		const inputTracks = await this.input.getTracks();
 		const outputTrackCounts = this.output.format.getSupportedTrackCounts();
 
+		let nVideo = 1;
+		let nAudio = 1;
+
 		for (const track of inputTracks) {
-			if (track.isVideoTrack() && this._options.video?.discard) {
-				this.discardedTracks.push({
-					track,
-					reason: 'discarded_by_user',
-				});
-				continue;
+			let trackOptions: ConversionVideoOptions | ConversionAudioOptions | undefined = undefined;
+			if (track.isVideoTrack()) {
+				if (this._options.video) {
+					if (typeof this._options.video === 'function') {
+						trackOptions = await this._options.video(track, nVideo);
+						validateVideoOptions(trackOptions);
+						nVideo++;
+					} else {
+						trackOptions = this._options.video;
+					}
+				}
+			} else if (track.isAudioTrack()) {
+				if (this._options.audio) {
+					if (typeof this._options.audio === 'function') {
+						trackOptions = await this._options.audio(track, nAudio);
+						validateAudioOptions(trackOptions);
+						nAudio++;
+					} else {
+						trackOptions = this._options.audio;
+					}
+				}
+			} else {
+				assert(false);
 			}
 
-			if (track.isAudioTrack() && this._options.audio?.discard) {
+			if (trackOptions?.discard) {
 				this.discardedTracks.push({
 					track,
 					reason: 'discarded_by_user',
@@ -372,9 +435,9 @@ export class Conversion {
 			}
 
 			if (track.isVideoTrack()) {
-				await this._processVideoTrack(track);
+				await this._processVideoTrack(track, (trackOptions ?? {}) as ConversionVideoOptions);
 			} else if (track.isAudioTrack()) {
-				await this._processAudioTrack(track);
+				await this._processAudioTrack(track, (trackOptions ?? {}) as ConversionAudioOptions);
 			}
 		}
 
@@ -443,7 +506,7 @@ export class Conversion {
 	}
 
 	/** @internal */
-	async _processVideoTrack(track: InputVideoTrack) {
+	async _processVideoTrack(track: InputVideoTrack, trackOptions: ConversionVideoOptions) {
 		const sourceCodec = track.codec;
 		if (!sourceCodec) {
 			this.discardedTracks.push({
@@ -455,7 +518,7 @@ export class Conversion {
 
 		let videoSource: VideoSource;
 
-		const totalRotation = normalizeRotation(track.rotation + (this._options.video?.rotate ?? 0));
+		const totalRotation = normalizeRotation(track.rotation + (trackOptions.rotate ?? 0));
 		const outputSupportsRotation = this.output.format.supportsVideoRotationMetadata;
 
 		const [originalWidth, originalHeight] = totalRotation % 180 === 0
@@ -469,22 +532,22 @@ export class Conversion {
 		// A lot of video encoders require that the dimensions be multiples of 2
 		const ceilToMultipleOfTwo = (value: number) => Math.ceil(value / 2) * 2;
 
-		if (this._options.video?.width !== undefined && this._options.video.height === undefined) {
-			width = ceilToMultipleOfTwo(this._options.video.width);
+		if (trackOptions.width !== undefined && trackOptions.height === undefined) {
+			width = ceilToMultipleOfTwo(trackOptions.width);
 			height = ceilToMultipleOfTwo(Math.round(width / aspectRatio));
-		} else if (this._options.video?.width === undefined && this._options.video?.height !== undefined) {
-			height = ceilToMultipleOfTwo(this._options.video.height);
+		} else if (trackOptions.width === undefined && trackOptions.height !== undefined) {
+			height = ceilToMultipleOfTwo(trackOptions.height);
 			width = ceilToMultipleOfTwo(Math.round(height * aspectRatio));
-		} else if (this._options.video?.width !== undefined && this._options.video.height !== undefined) {
-			width = ceilToMultipleOfTwo(this._options.video.width);
-			height = ceilToMultipleOfTwo(this._options.video.height);
+		} else if (trackOptions.width !== undefined && trackOptions.height !== undefined) {
+			width = ceilToMultipleOfTwo(trackOptions.width);
+			height = ceilToMultipleOfTwo(trackOptions.height);
 		}
 
 		const firstTimestamp = await track.getFirstTimestamp();
-		const needsTranscode = !!this._options.video?.forceTranscode
+		const needsTranscode = !!trackOptions.forceTranscode
 			|| this._startTimestamp > 0
 			|| firstTimestamp < 0
-			|| !!this._options.video?.frameRate;
+			|| !!trackOptions.frameRate;
 		const needsRerender = width !== originalWidth
 			|| height !== originalHeight
 			|| (totalRotation !== 0 && !outputSupportsRotation);
@@ -492,10 +555,10 @@ export class Conversion {
 		let videoCodecs = this.output.format.getSupportedVideoCodecs();
 		if (
 			!needsTranscode
-			&& !this._options.video?.bitrate
+			&& !trackOptions.bitrate
 			&& !needsRerender
 			&& videoCodecs.includes(sourceCodec)
-			&& (!this._options.video?.codec || this._options.video?.codec === sourceCodec)
+			&& (!trackOptions.codec || trackOptions.codec === sourceCodec)
 		) {
 			// Fast path, we can simply copy over the encoded packets
 
@@ -540,11 +603,11 @@ export class Conversion {
 				return;
 			}
 
-			if (this._options.video?.codec) {
-				videoCodecs = videoCodecs.filter(codec => codec === this._options.video?.codec);
+			if (trackOptions.codec) {
+				videoCodecs = videoCodecs.filter(codec => codec === trackOptions.codec);
 			}
 
-			const bitrate = this._options.video?.bitrate ?? QUALITY_HIGH;
+			const bitrate = trackOptions.bitrate ?? QUALITY_HIGH;
 
 			const encodableCodec = await getFirstEncodableVideoCodec(videoCodecs, { width, height, bitrate });
 			if (!encodableCodec) {
@@ -571,12 +634,12 @@ export class Conversion {
 					const sink = new CanvasSink(track, {
 						width,
 						height,
-						fit: this._options.video?.fit ?? 'fill',
+						fit: trackOptions.fit ?? 'fill',
 						rotation: totalRotation, // Bake the rotation into the output
 						poolSize: 1,
 					});
 					const iterator = sink.canvases(this._startTimestamp, this._endTimestamp);
-					const frameRate = this._options.video?.frameRate;
+					const frameRate = trackOptions.frameRate;
 
 					let lastCanvas: HTMLCanvasElement | OffscreenCanvas | null = null;
 					let lastCanvasTimestamp: number | null = null;
@@ -661,7 +724,7 @@ export class Conversion {
 					await this._started;
 
 					const sink = new VideoSampleSink(track);
-					const frameRate = this._options.video?.frameRate;
+					const frameRate = trackOptions.frameRate;
 
 					let lastSample: VideoSample | null = null;
 					let lastSampleTimestamp: number | null = null;
@@ -744,7 +807,7 @@ export class Conversion {
 		}
 
 		this.output.addVideoTrack(videoSource, {
-			frameRate: this._options.video?.frameRate,
+			frameRate: trackOptions.frameRate,
 			languageCode: track.languageCode,
 			rotation: needsRerender ? 0 : totalRotation, // Rerendering will bake the rotation into the output
 		});
@@ -755,7 +818,7 @@ export class Conversion {
 	}
 
 	/** @internal */
-	async _processAudioTrack(track: InputAudioTrack) {
+	async _processAudioTrack(track: InputAudioTrack, trackOptions: ConversionAudioOptions) {
 		const sourceCodec = track.codec;
 		if (!sourceCodec) {
 			this.discardedTracks.push({
@@ -772,8 +835,8 @@ export class Conversion {
 
 		const firstTimestamp = await track.getFirstTimestamp();
 
-		let numberOfChannels = this._options.audio?.numberOfChannels ?? originalNumberOfChannels;
-		let sampleRate = this._options.audio?.sampleRate ?? originalSampleRate;
+		let numberOfChannels = trackOptions.numberOfChannels ?? originalNumberOfChannels;
+		let sampleRate = trackOptions.sampleRate ?? originalSampleRate;
 		let needsResample = numberOfChannels !== originalNumberOfChannels
 			|| sampleRate !== originalSampleRate
 			|| this._startTimestamp > 0
@@ -781,11 +844,11 @@ export class Conversion {
 
 		let audioCodecs = this.output.format.getSupportedAudioCodecs();
 		if (
-			!this._options.audio?.forceTranscode
-			&& !this._options.audio?.bitrate
+			!trackOptions.forceTranscode
+			&& !trackOptions.bitrate
 			&& !needsResample
 			&& audioCodecs.includes(sourceCodec)
-			&& (!this._options.audio?.codec || this._options.audio.codec === sourceCodec)
+			&& (!trackOptions.codec || trackOptions.codec === sourceCodec)
 		) {
 			// Fast path, we can simply copy over the encoded packets
 
@@ -832,11 +895,11 @@ export class Conversion {
 
 			let codecOfChoice: AudioCodec | null = null;
 
-			if (this._options.audio?.codec) {
-				audioCodecs = audioCodecs.filter(codec => codec === this._options.audio!.codec);
+			if (trackOptions.codec) {
+				audioCodecs = audioCodecs.filter(codec => codec === trackOptions.codec);
 			}
 
-			const bitrate = this._options.audio?.bitrate ?? QUALITY_HIGH;
+			const bitrate = trackOptions.bitrate ?? QUALITY_HIGH;
 
 			const encodableCodecs = await getEncodableAudioCodecs(audioCodecs, {
 				numberOfChannels,

src/index.ts

@@ -84,7 +84,7 @@ export {
 	getFirstEncodableSubtitleCodec,
 } from './codec';
 export { Target, BufferTarget, StreamTarget, StreamTargetChunk, StreamTargetOptions } from './target';
-export { Rotation, AnyIterable, SetRequired } from './misc';
+export { Rotation, AnyIterable, SetRequired, MaybePromise } from './misc';
 export {
 	Source,
 	BufferSource,
@@ -135,7 +135,7 @@ export {
 	AudioBufferSink,
 	WrappedAudioBuffer,
 } from './media-sink';
-export { ConversionOptions, Conversion } from './conversion';
+export { Conversion, ConversionOptions, ConversionVideoOptions, ConversionAudioOptions } from './conversion';
 export {
 	CustomVideoDecoder,
 	CustomAudioDecoder,

src/misc.ts

@@ -610,3 +610,9 @@ export const isSafari = () => {
 	isSafariCache = result;
 	return result;
 };
+
+/**
+ * T or a promise that resolves to T.
+ * @public
+ */
+export type MaybePromise<T> = T | Promise<T>;