mediabunny/src/media-source.ts

/*!
 * Copyright (c) 2025-present, Vanilagy and contributors
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at https://mozilla.org/MPL/2.0/.
 */

import {
	AUDIO_CODECS,
	AudioCodec,
	parsePcmCodec,
	PCM_AUDIO_CODECS,
	PcmAudioCodec,
	SUBTITLE_CODECS,
	SubtitleCodec,
	VIDEO_CODECS,
	VideoCodec,
} from './codec';
import { OutputAudioTrack, OutputSubtitleTrack, OutputTrack, OutputVideoTrack } from './output';
import { assert, assertNever, CallSerializer, clamp, promiseWithResolvers, setInt24, setUint24 } from './misc';
import { Muxer } from './muxer';
import { SubtitleParser } from './subtitles';
import { toAlaw, toUlaw } from './pcm';
import {
	CustomVideoEncoder,
	CustomAudioEncoder,
	customVideoEncoders,
	customAudioEncoders,
} from './custom-coder';
import { EncodedPacket } from './packet';
import { AudioSample, VideoSample } from './sample';
import {
	AudioEncodingConfig,
	buildAudioEncoderConfig,
	buildVideoEncoderConfig,
	validateAudioEncodingConfig,
	validateVideoEncodingConfig,
	VideoEncodingConfig,
} from './encode';

/**
 * Base class for media sources. Media sources are used to add media samples to an output file.
 * @group Media sources
 * @public
 */
export abstract class MediaSource {
	/** @internal */
	_connectedTrack: OutputTrack | null = null;
	/** @internal */
	_closingPromise: Promise<void> | null = null;
	/** @internal */
	_closed = false;
	/**
	 * @internal
	 * A time offset in seconds that is added to all timestamps generated by this source.
	 */
	_timestampOffset = 0;

	/** @internal */
	_ensureValidAdd() {
		if (!this._connectedTrack) {
			throw new Error('Source is not connected to an output track.');
		}

		if (this._connectedTrack.output.state === 'canceled') {
			throw new Error('Output has been canceled.');
		}

		if (this._connectedTrack.output.state === 'finalizing' || this._connectedTrack.output.state === 'finalized') {
			throw new Error('Output has been finalized.');
		}

		if (this._connectedTrack.output.state === 'pending') {
			throw new Error('Output has not started.');
		}

		if (this._closed) {
			throw new Error('Source is closed.');
		}
	}

	/** @internal */
	async _start() {}
	/** @internal */
	// eslint-disable-next-line @typescript-eslint/no-unused-vars
	async _flushAndClose(forceClose: boolean) {}

	/**
	 * Closes this source. This prevents future samples from being added and signals to the output file that no further
	 * samples will come in for this track. Calling `.close()` is optional but recommended after adding the
	 * last sample - for improved performance and reduced memory usage.
	 */
	close() {
		if (this._closingPromise) {
			return;
		}

		const connectedTrack = this._connectedTrack;

		if (!connectedTrack) {
			throw new Error('Cannot call close without connecting the source to an output track.');
		}

		if (connectedTrack.output.state === 'pending') {
			throw new Error('Cannot call close before output has been started.');
		}

		this._closingPromise = (async () => {
			await this._flushAndClose(false);

			this._closed = true;

			if (connectedTrack.output.state === 'finalizing' || connectedTrack.output.state === 'finalized') {
				return;
			}

			connectedTrack.output._muxer.onTrackClose(connectedTrack);
		})();
	}

	/** @internal */
	async _flushOrWaitForOngoingClose(forceClose: boolean) {
		if (this._closingPromise) {
			// Since closing also flushes, we don't want to do it twice
			return this._closingPromise;
		} else {
			return this._flushAndClose(forceClose);
		}
	}
}

/**
 * Base class for video sources - sources for video tracks.
 * @group Media sources
 * @public
 */
export abstract class VideoSource extends MediaSource {
	/** @internal */
	override _connectedTrack: OutputVideoTrack | null = null;
	/** @internal */
	_codec: VideoCodec;

	/** Internal constructor. */
	constructor(codec: VideoCodec) {
		super();

		if (!VIDEO_CODECS.includes(codec)) {
			throw new TypeError(`Invalid video codec '${codec}'. Must be one of: ${VIDEO_CODECS.join(', ')}.`);
		}

		this._codec = codec;
	}
}

/**
 * The most basic video source; can be used to directly pipe encoded packets into the output file.
 * @group Media sources
 * @public
 */
export class EncodedVideoPacketSource extends VideoSource {
	/** Creates a new {@link EncodedVideoPacketSource} whose packets are encoded using `codec`. */
	constructor(codec: VideoCodec) {
		super(codec);
	}

	/**
	 * Adds an encoded packet to the output video track. Packets must be added in *decode order*, while a packet's
	 * timestamp must be its *presentation timestamp*. B-frames are handled automatically.
	 *
	 * @param meta - Additional metadata from the encoder. You should pass this for the first call, including a valid
	 * decoder config.
	 *
	 * @returns A Promise that resolves once the output is ready to receive more samples. You should await this Promise
	 * to respect writer and encoder backpressure.
	 */
	add(packet: EncodedPacket, meta?: EncodedVideoChunkMetadata) {
		if (!(packet instanceof EncodedPacket)) {
			throw new TypeError('packet must be an EncodedPacket.');
		}
		if (packet.isMetadataOnly) {
			throw new TypeError('Metadata-only packets cannot be added.');
		}
		if (meta !== undefined && (!meta || typeof meta !== 'object')) {
			throw new TypeError('meta, when provided, must be an object.');
		}

		this._ensureValidAdd();
		return this._connectedTrack!.output._muxer.addEncodedVideoPacket(this._connectedTrack!, packet, meta);
	}
}

class VideoEncoderWrapper {
	private ensureEncoderPromise: Promise<void> | null = null;
	private encoderInitialized = false;
	private encoder: VideoEncoder | null = null;
	private muxer: Muxer | null = null;
	private lastMultipleOfKeyFrameInterval = -1;
	private codedWidth: number | null = null;
	private codedHeight: number | null = null;
	private resizeCanvas: HTMLCanvasElement | OffscreenCanvas | null = null;

	private customEncoder: CustomVideoEncoder | null = null;
	private customEncoderCallSerializer = new CallSerializer();
	private customEncoderQueueSize = 0;

	/**
	 * Encoders typically throw their errors "out of band", meaning asynchronously in some other execution context.
	 * However, we want to surface these errors to the user within the normal control flow, so they don't go uncaught.
	 * So, we keep track of the encoder error and throw it as soon as we get the chance.
	 */
	private encoderError: Error | null = null;

	constructor(private source: VideoSource, private encodingConfig: VideoEncodingConfig) {}

	async add(videoSample: VideoSample, shouldClose: boolean, encodeOptions?: VideoEncoderEncodeOptions) {
		try {
			this.checkForEncoderError();
			this.source._ensureValidAdd();

			// Ensure video sample size remains constant
			if (this.codedWidth !== null && this.codedHeight !== null) {
				if (videoSample.codedWidth !== this.codedWidth || videoSample.codedHeight !== this.codedHeight) {
					const sizeChangeBehavior = this.encodingConfig.sizeChangeBehavior ?? 'deny';

					if (sizeChangeBehavior === 'passThrough') {
						// Do nada
					} else if (sizeChangeBehavior === 'deny') {
						throw new Error(
							`Video sample size must remain constant. Expected ${this.codedWidth}x${this.codedHeight},`
							+ ` got ${videoSample.codedWidth}x${videoSample.codedHeight}. To allow the sample size to`
							+ ` change over time, set \`sizeChangeBehavior\` to a value other than 'strict' in the`
							+ ` encoding options.`,
						);
					} else {
						let canvasIsNew = false;

						if (!this.resizeCanvas) {
							if (typeof document !== 'undefined') {
								// Prefer an HTMLCanvasElement
								this.resizeCanvas = document.createElement('canvas');
								this.resizeCanvas.width = this.codedWidth;
								this.resizeCanvas.height = this.codedHeight;
							} else {
								this.resizeCanvas = new OffscreenCanvas(this.codedWidth, this.codedHeight);
							}

							canvasIsNew = true;
						}

						const context = this.resizeCanvas.getContext('2d', { alpha: false }) as
							CanvasRenderingContext2D | OffscreenCanvasRenderingContext2D;
						assert(context);

						if (!canvasIsNew) {
							context.clearRect(0, 0, this.codedWidth, this.codedHeight);
						}

						videoSample.drawWithFit(context, { fit: sizeChangeBehavior });

						if (shouldClose) {
							videoSample.close();
						}

						videoSample = new VideoSample(this.resizeCanvas, {
							timestamp: videoSample.timestamp,
							duration: videoSample.duration,
							rotation: videoSample.rotation,
						});
						shouldClose = true;
					}
				}
			} else {
				this.codedWidth = videoSample.codedWidth;
				this.codedHeight = videoSample.codedHeight;
			}

			if (!this.encoderInitialized) {
				if (!this.ensureEncoderPromise) {
					void this.ensureEncoder(videoSample);
				}

				// No, this "if" statement is not useless. Sometimes, the above call to `ensureEncoder` might have
				// synchronously completed and the encoder is already initialized. In this case, we don't need to await
				// the promise anymore. This also fixes nasty async race condition bugs when multiple code paths are
				// calling this method: It's important that the call that initialized the encoder go through this
				// code first.
				if (!this.encoderInitialized) {
					await this.ensureEncoderPromise;
				}
			}
			assert(this.encoderInitialized);

			const keyFrameInterval = this.encodingConfig.keyFrameInterval ?? 5;
			const multipleOfKeyFrameInterval = Math.floor(videoSample.timestamp / keyFrameInterval);

			// Ensure a key frame every keyFrameInterval seconds. It is important that all video tracks follow the same
			// "key frame" rhythm, because aligned key frames are required to start new fragments in ISOBMFF or clusters
			// in Matroska (or at least desirable).
			const finalEncodeOptions = {
				...encodeOptions,
				keyFrame: encodeOptions?.keyFrame
					|| keyFrameInterval === 0
					|| multipleOfKeyFrameInterval !== this.lastMultipleOfKeyFrameInterval,
			};
			this.lastMultipleOfKeyFrameInterval = multipleOfKeyFrameInterval;

			if (this.customEncoder) {
				this.customEncoderQueueSize++;

				// We clone the sample so it cannot be closed on us from the outside before it reaches the encoder
				const clonedSample = videoSample.clone();

				const promise = this.customEncoderCallSerializer
					.call(() => this.customEncoder!.encode(clonedSample, finalEncodeOptions))
					.then(() => this.customEncoderQueueSize--)
					.catch((error: Error) => this.encoderError ??= error)
					.finally(() => {
						clonedSample.close();
						// `videoSample` gets closed in the finally block at the end of the method
					});

				if (this.customEncoderQueueSize >= 4) {
					await promise;
				}
			} else {
				assert(this.encoder);
				const videoFrame = videoSample.toVideoFrame();
				this.encoder.encode(videoFrame, finalEncodeOptions);
				videoFrame.close();

				if (shouldClose) {
					videoSample.close();
				}

				// We need to do this after sending the frame to the encoder as the frame otherwise might be closed
				if (this.encoder.encodeQueueSize >= 4) {
					await new Promise(resolve => this.encoder!.addEventListener('dequeue', resolve, { once: true }));
				}
			}

			await this.muxer!.mutex.currentPromise; // Allow the writer to apply backpressure
		} finally {
			if (shouldClose) {
				// Make sure it's always closed, even if there was an error
				videoSample.close();
			}
		}
	}

	private async ensureEncoder(videoSample: VideoSample) {
		if (this.encoder) {
			return;
		}

		const encoderError = new Error();
		return this.ensureEncoderPromise = (async () => {
			const encoderConfig = buildVideoEncoderConfig({
				width: videoSample.codedWidth,
				height: videoSample.codedHeight,
				...this.encodingConfig,
				framerate: this.source._connectedTrack?.metadata.frameRate,
			});
			this.encodingConfig.onEncoderConfig?.(encoderConfig);

			const MatchingCustomEncoder = customVideoEncoders.find(x => x.supports(
				this.encodingConfig.codec,
				encoderConfig,
			));

			if (MatchingCustomEncoder) {
				// @ts-expect-error "Can't create instance of abstract class 🤓"
				this.customEncoder = new MatchingCustomEncoder() as CustomVideoEncoder;
				// @ts-expect-error It's technically readonly
				this.customEncoder.codec = this.encodingConfig.codec;
				// @ts-expect-error It's technically readonly
				this.customEncoder.config = encoderConfig;
				// @ts-expect-error It's technically readonly
				this.customEncoder.onPacket = (packet, meta) => {
					if (!(packet instanceof EncodedPacket)) {
						throw new TypeError('The first argument passed to onPacket must be an EncodedPacket.');
					}
					if (meta !== undefined && (!meta || typeof meta !== 'object')) {
						throw new TypeError('The second argument passed to onPacket must be an object or undefined.');
					}

					this.encodingConfig.onEncodedPacket?.(packet, meta);
					void this.muxer!.addEncodedVideoPacket(this.source._connectedTrack!, packet, meta);
				};

				await this.customEncoder.init();
			} else {
				if (typeof VideoEncoder === 'undefined') {
					throw new Error('VideoEncoder is not supported by this browser.');
				}

				const support = await VideoEncoder.isConfigSupported(encoderConfig);
				if (!support.supported) {
					throw new Error(
						`This specific encoder configuration (${encoderConfig.codec}, ${encoderConfig.bitrate} bps,`
						+ ` ${encoderConfig.width}x${encoderConfig.height}, hardware acceleration:`
						+ ` ${encoderConfig.hardwareAcceleration ?? 'no-preference'}) is not supported by this browser.`
						+ ` Consider using another codec or changing your video parameters.`,
					);
				}

				this.encoder = new VideoEncoder({
					output: (chunk, meta) => {
						const packet = EncodedPacket.fromEncodedChunk(chunk);

						this.encodingConfig.onEncodedPacket?.(packet, meta);
						void this.muxer!.addEncodedVideoPacket(this.source._connectedTrack!, packet, meta);
					},
					error: (error) => {
						error.stack = encoderError.stack; // Provide a more useful stack trace
						this.encoderError ??= error;
					},
				});
				this.encoder.configure(encoderConfig);
			}

			assert(this.source._connectedTrack);
			this.muxer = this.source._connectedTrack.output._muxer;

			this.encoderInitialized = true;
		})();
	}

	async flushAndClose(forceClose: boolean) {
		if (!forceClose) this.checkForEncoderError();

		if (this.customEncoder) {
			if (!forceClose) {
				void this.customEncoderCallSerializer.call(() => this.customEncoder!.flush());
			}

			await this.customEncoderCallSerializer.call(() => this.customEncoder!.close());
		} else if (this.encoder) {
			if (!forceClose) {
				await this.encoder.flush();
			}

			if (this.encoder.state !== 'closed') {
				this.encoder.close();
			}
		}

		if (!forceClose) this.checkForEncoderError();
	}

	getQueueSize() {
		if (this.customEncoder) {
			return this.customEncoderQueueSize;
		} else {
			return this.encoder?.encodeQueueSize ?? 0;
		}
	}

	checkForEncoderError() {
		if (this.encoderError) {
			this.encoderError.stack = new Error().stack; // Provide an even more useful stack trace
			throw this.encoderError;
		}
	}
}

/**
 * This source can be used to add raw, unencoded video samples (frames) to an output video track. These frames will
 * automatically be encoded and then piped into the output.
 * @group Media sources
 * @public
 */
export class VideoSampleSource extends VideoSource {
	/** @internal */
	private _encoder: VideoEncoderWrapper;

	/**
	 * Creates a new {@link VideoSampleSource} whose samples are encoded according to the specified
	 * {@link VideoEncodingConfig}.
	 */
	constructor(encodingConfig: VideoEncodingConfig) {
		validateVideoEncodingConfig(encodingConfig);

		super(encodingConfig.codec);
		this._encoder = new VideoEncoderWrapper(this, encodingConfig);
	}

	/**
	 * Encodes a video sample (frame) and then adds it to the output.
	 *
	 * @returns A Promise that resolves once the output is ready to receive more samples. You should await this Promise
	 * to respect writer and encoder backpressure.
	 */
	add(videoSample: VideoSample, encodeOptions?: VideoEncoderEncodeOptions) {
		if (!(videoSample instanceof VideoSample)) {
			throw new TypeError('videoSample must be a VideoSample.');
		}

		return this._encoder.add(videoSample, false, encodeOptions);
	}

	/** @internal */
	override _flushAndClose(forceClose: boolean) {
		return this._encoder.flushAndClose(forceClose);
	}
}

/**
 * This source can be used to add video frames to the output track from a fixed canvas element. Since canvases are often
 * used for rendering, this source provides a convenient wrapper around {@link VideoSampleSource}.
 * @group Media sources
 * @public
 */
export class CanvasSource extends VideoSource {
	/** @internal */
	private _encoder: VideoEncoderWrapper;
	/** @internal */
	private _canvas: HTMLCanvasElement | OffscreenCanvas;

	/**
	 * Creates a new {@link CanvasSource} from a canvas element or `OffscreenCanvas` whose samples are encoded
	 * according to the specified {@link VideoEncodingConfig}.
	 */
	constructor(canvas: HTMLCanvasElement | OffscreenCanvas, encodingConfig: VideoEncodingConfig) {
		if (
			!(typeof HTMLCanvasElement !== 'undefined' && canvas instanceof HTMLCanvasElement)
			&& !(typeof OffscreenCanvas !== 'undefined' && canvas instanceof OffscreenCanvas)
		) {
			throw new TypeError('canvas must be an HTMLCanvasElement or OffscreenCanvas.');
		}
		validateVideoEncodingConfig(encodingConfig);

		super(encodingConfig.codec);
		this._encoder = new VideoEncoderWrapper(this, encodingConfig);
		this._canvas = canvas;
	}

	/**
	 * Captures the current canvas state as a video sample (frame), encodes it and adds it to the output.
	 *
	 * @param timestamp - The timestamp of the sample, in seconds.
	 * @param duration - The duration of the sample, in seconds.
	 *
	 * @returns A Promise that resolves once the output is ready to receive more samples. You should await this Promise
	 * to respect writer and encoder backpressure.
	 */
	add(timestamp: number, duration = 0, encodeOptions?: VideoEncoderEncodeOptions) {
		if (!Number.isFinite(timestamp) || timestamp < 0) {
			throw new TypeError('timestamp must be a non-negative number.');
		}
		if (!Number.isFinite(duration) || duration < 0) {
			throw new TypeError('duration must be a non-negative number.');
		}

		const sample = new VideoSample(this._canvas, { timestamp, duration });
		return this._encoder.add(sample, true, encodeOptions);
	}

	/** @internal */
	override _flushAndClose(forceClose: boolean) {
		return this._encoder.flushAndClose(forceClose);
	}
}

/**
 * Video source that encodes the frames of a
 * [`MediaStreamVideoTrack`](https://developer.mozilla.org/en-US/docs/Web/API/MediaStreamTrack) and pipes them into the
 * output. This is useful for capturing live or real-time data such as webcams or screen captures. Frames will
 * automatically start being captured once the connected {@link Output} is started, and will keep being captured until
 * the {@link Output} is finalized or this source is closed.
 * @group Media sources
 * @public
 */
export class MediaStreamVideoTrackSource extends VideoSource {
	/** @internal */
	private _encoder: VideoEncoderWrapper;
	/** @internal */
	private _abortController: AbortController | null = null;
	/** @internal */
	private _track: MediaStreamVideoTrack;
	/** @internal */
	private _workerTrackId: number | null = null;
	/** @internal */
	private _workerListener: ((event: MessageEvent) => void) | null = null;
	/** @internal */
	private _promiseWithResolvers = promiseWithResolvers();
	/** @internal */
	private _errorPromiseAccessed = false;

	/** A promise that rejects upon any error within this source. This promise never resolves. */
	get errorPromise() {
		this._errorPromiseAccessed = true;
		return this._promiseWithResolvers.promise;
	}

	/**
	 * Creates a new {@link MediaStreamVideoTrackSource} from a
	 * [`MediaStreamVideoTrack`](https://developer.mozilla.org/en-US/docs/Web/API/MediaStreamTrack), which will pull
	 * video samples from the stream in real time and encode them according to {@link VideoEncodingConfig}.
	 */
	constructor(track: MediaStreamVideoTrack, encodingConfig: VideoEncodingConfig) {
		if (!(track instanceof MediaStreamTrack) || track.kind !== 'video') {
			throw new TypeError('track must be a video MediaStreamTrack.');
		}
		validateVideoEncodingConfig(encodingConfig);

		encodingConfig = {
			...encodingConfig,
			latencyMode: 'realtime',
		};

		super(encodingConfig.codec);
		this._encoder = new VideoEncoderWrapper(this, encodingConfig);
		this._track = track;
	}

	/** @internal */
	override async _start() {
		if (!this._errorPromiseAccessed) {
			console.warn(
				'Make sure not to ignore the `errorPromise` field on MediaStreamVideoTrackSource, so that any internal'
				+ ' errors get bubbled up properly.',
			);
		}

		this._abortController = new AbortController();

		let firstVideoFrameTimestamp: number | null = null;
		let errored = false;

		const onVideoFrame = (videoFrame: VideoFrame) => {
			if (errored) {
				videoFrame.close();
				return;
			}

			if (firstVideoFrameTimestamp === null) {
				firstVideoFrameTimestamp = videoFrame.timestamp / 1e6;

				const muxer = this._connectedTrack!.output._muxer;
				if (muxer.firstMediaStreamTimestamp === null) {
					muxer.firstMediaStreamTimestamp = performance.now() / 1000;
					this._timestampOffset = -firstVideoFrameTimestamp;
				} else {
					this._timestampOffset = (performance.now() / 1000 - muxer.firstMediaStreamTimestamp)
						- firstVideoFrameTimestamp;
				}
			}

			if (this._encoder.getQueueSize() >= 4) {
				// Drop frames if the encoder is overloaded
				videoFrame.close();
				return;
			}

			void this._encoder.add(new VideoSample(videoFrame), true)
				.catch((error) => {
					errored = true;

					this._abortController?.abort();
					this._promiseWithResolvers.reject(error);

					if (this._workerTrackId !== null) {
						// Tell the worker to stop the track
						sendMessageToMediaStreamTrackProcessorWorker({
							type: 'stopTrack',
							trackId: this._workerTrackId,
						});
					}
				});
		};

		if (typeof MediaStreamTrackProcessor !== 'undefined') {
			// We can do it here directly, perfect
			const processor = new MediaStreamTrackProcessor({ track: this._track });
			const consumer = new WritableStream<VideoFrame>({ write: onVideoFrame });

			processor.readable.pipeTo(consumer, {
				signal: this._abortController.signal,
			}).catch((error) => {
				// Handle AbortError silently
				if (error instanceof DOMException && error.name === 'AbortError') return;

				this._promiseWithResolvers.reject(error);
			});
		} else {
			// It might still be supported in a worker, so let's check that
			const supportedInWorker = await mediaStreamTrackProcessorIsSupportedInWorker();

			if (supportedInWorker) {
				this._workerTrackId = nextMediaStreamTrackProcessorWorkerId++;

				sendMessageToMediaStreamTrackProcessorWorker({
					type: 'videoTrack',
					trackId: this._workerTrackId,
					track: this._track,
				}, [this._track]);

				this._workerListener = (event: MessageEvent) => {
					const message = event.data as MediaStreamTrackProcessorWorkerMessage;

					if (message.type === 'videoFrame' && message.trackId === this._workerTrackId) {
						onVideoFrame(message.videoFrame);
					} else if (message.type === 'error' && message.trackId === this._workerTrackId) {
						this._promiseWithResolvers.reject(message.error);
					}
				};

				mediaStreamTrackProcessorWorker!.addEventListener('message', this._workerListener);
			} else {
				throw new Error('MediaStreamTrackProcessor is required but not supported by this browser.');
			}
		}
	}

	/** @internal */
	override async _flushAndClose(forceClose: boolean) {
		if (this._abortController) {
			this._abortController.abort();
			this._abortController = null;
		}

		if (this._workerTrackId !== null) {
			assert(this._workerListener);

			sendMessageToMediaStreamTrackProcessorWorker({
				type: 'stopTrack',
				trackId: this._workerTrackId,
			});

			// Wait for the worker to stop the track
			await new Promise<void>((resolve) => {
				const listener = (event: MessageEvent) => {
					const message = event.data as MediaStreamTrackProcessorWorkerMessage;

					if (message.type === 'trackStopped' && message.trackId === this._workerTrackId) {
						assert(this._workerListener);
						mediaStreamTrackProcessorWorker!.removeEventListener('message', this._workerListener);
						mediaStreamTrackProcessorWorker!.removeEventListener('message', listener);

						resolve();
					}
				};

				mediaStreamTrackProcessorWorker!.addEventListener('message', listener);
			});
		}

		await this._encoder.flushAndClose(forceClose);
	}
}

/**
 * Base class for audio sources - sources for audio tracks.
 * @group Media sources
 * @public
 */
export abstract class AudioSource extends MediaSource {
	/** @internal */
	override _connectedTrack: OutputAudioTrack | null = null;
	/** @internal */
	_codec: AudioCodec;

	/** Internal constructor. */
	constructor(codec: AudioCodec) {
		super();

		if (!AUDIO_CODECS.includes(codec)) {
			throw new TypeError(`Invalid audio codec '${codec}'. Must be one of: ${AUDIO_CODECS.join(', ')}.`);
		}

		this._codec = codec;
	}
}

/**
 * The most basic audio source; can be used to directly pipe encoded packets into the output file.
 * @group Media sources
 * @public
 */
export class EncodedAudioPacketSource extends AudioSource {
	/** Creates a new {@link EncodedAudioPacketSource} whose packets are encoded using `codec`. */
	constructor(codec: AudioCodec) {
		super(codec);
	}

	/**
	 * Adds an encoded packet to the output audio track. Packets must be added in *decode order*.
	 *
	 * @param meta - Additional metadata from the encoder. You should pass this for the first call, including a valid
	 * decoder config.
	 *
	 * @returns A Promise that resolves once the output is ready to receive more samples. You should await this Promise
	 * to respect writer and encoder backpressure.
	 */
	add(packet: EncodedPacket, meta?: EncodedAudioChunkMetadata) {
		if (!(packet instanceof EncodedPacket)) {
			throw new TypeError('packet must be an EncodedPacket.');
		}
		if (packet.isMetadataOnly) {
			throw new TypeError('Metadata-only packets cannot be added.');
		}
		if (meta !== undefined && (!meta || typeof meta !== 'object')) {
			throw new TypeError('meta, when provided, must be an object.');
		}

		this._ensureValidAdd();
		return this._connectedTrack!.output._muxer.addEncodedAudioPacket(this._connectedTrack!, packet, meta);
	}
}

class AudioEncoderWrapper {
	private ensureEncoderPromise: Promise<void> | null = null;
	private encoderInitialized = false;
	private encoder: AudioEncoder | null = null;
	private muxer: Muxer | null = null;
	private lastNumberOfChannels: number | null = null;
	private lastSampleRate: number | null = null;

	private isPcmEncoder = false;
	private outputSampleSize: number | null = null;
	private writeOutputValue: ((view: DataView, byteOffset: number, value: number) => void) | null = null;

	private customEncoder: CustomAudioEncoder | null = null;
	private customEncoderCallSerializer = new CallSerializer();
	private customEncoderQueueSize = 0;

	/**
	 * Encoders typically throw their errors "out of band", meaning asynchronously in some other execution context.
	 * However, we want to surface these errors to the user within the normal control flow, so they don't go uncaught.
	 * So, we keep track of the encoder error and throw it as soon as we get the chance.
	 */
	private encoderError: Error | null = null;

	constructor(private source: AudioSource, private encodingConfig: AudioEncodingConfig) {}

	async add(audioSample: AudioSample, shouldClose: boolean) {
		try {
			this.checkForEncoderError();
			this.source._ensureValidAdd();

			// Ensure audio parameters remain constant
			if (this.lastNumberOfChannels !== null && this.lastSampleRate !== null) {
				if (
					audioSample.numberOfChannels !== this.lastNumberOfChannels
					|| audioSample.sampleRate !== this.lastSampleRate
				) {
					throw new Error(
						`Audio parameters must remain constant. Expected ${this.lastNumberOfChannels} channels at`
						+ ` ${this.lastSampleRate} Hz, got ${audioSample.numberOfChannels} channels at`
						+ ` ${audioSample.sampleRate} Hz.`,
					);
				}
			} else {
				this.lastNumberOfChannels = audioSample.numberOfChannels;
				this.lastSampleRate = audioSample.sampleRate;
			}

			if (!this.encoderInitialized) {
				if (!this.ensureEncoderPromise) {
					void this.ensureEncoder(audioSample);
				}

				// No, this "if" statement is not useless. Sometimes, the above call to `ensureEncoder` might have
				// synchronously completed and the encoder is already initialized. In this case, we don't need to await
				// the promise anymore. This also fixes nasty async race condition bugs when multiple code paths are
				// calling this method: It's important that the call that initialized the encoder go through this
				// code first.
				if (!this.encoderInitialized) {
					await this.ensureEncoderPromise;
				}
			}
			assert(this.encoderInitialized);

			if (this.customEncoder) {
				this.customEncoderQueueSize++;

				// We clone the sample so it cannot be closed on us from the outside before it reaches the encoder
				const clonedSample = audioSample.clone();

				const promise = this.customEncoderCallSerializer
					.call(() => this.customEncoder!.encode(clonedSample))
					.then(() => this.customEncoderQueueSize--)
					.catch((error: Error) => this.encoderError ??= error)
					.finally(() => {
						clonedSample.close();
						// `audioSample` gets closed in the finally block at the end of the method
					});

				if (this.customEncoderQueueSize >= 4) {
					await promise;
				}

				await this.muxer!.mutex.currentPromise; // Allow the writer to apply backpressure
			} else if (this.isPcmEncoder) {
				await this.doPcmEncoding(audioSample, shouldClose);
			} else {
				assert(this.encoder);
				const audioData = audioSample.toAudioData();
				this.encoder.encode(audioData);
				audioData.close();

				if (shouldClose) {
					audioSample.close();
				}

				if (this.encoder.encodeQueueSize >= 4) {
					await new Promise(resolve => this.encoder!.addEventListener('dequeue', resolve, { once: true }));
				}

				await this.muxer!.mutex.currentPromise; // Allow the writer to apply backpressure
			}
		} finally {
			if (shouldClose) {
				// Make sure it's always closed, even if there was an error
				audioSample.close();
			}
		}
	}

	private async doPcmEncoding(audioSample: AudioSample, shouldClose: boolean) {
		assert(this.outputSampleSize);
		assert(this.writeOutputValue);

		// Need to extract data from the audio data before we close it
		const { numberOfChannels, numberOfFrames, sampleRate, timestamp } = audioSample;

		const CHUNK_SIZE = 2048;
		const outputs: {
			frameCount: number;
			view: DataView;
		}[] = [];

		// Prepare all of the output buffers, each being bounded by CHUNK_SIZE so we don't generate huge packets
		for (let frame = 0; frame < numberOfFrames; frame += CHUNK_SIZE) {
			const frameCount = Math.min(CHUNK_SIZE, audioSample.numberOfFrames - frame);
			const outputSize = frameCount * numberOfChannels * this.outputSampleSize;
			const outputBuffer = new ArrayBuffer(outputSize);
			const outputView = new DataView(outputBuffer);

			outputs.push({ frameCount, view: outputView });
		}

		const allocationSize = audioSample.allocationSize(({ planeIndex: 0, format: 'f32-planar' }));
		const floats = new Float32Array(allocationSize / Float32Array.BYTES_PER_ELEMENT);

		for (let i = 0; i < numberOfChannels; i++) {
			audioSample.copyTo(floats, { planeIndex: i, format: 'f32-planar' });

			for (let j = 0; j < outputs.length; j++) {
				const { frameCount, view } = outputs[j]!;

				for (let k = 0; k < frameCount; k++) {
					this.writeOutputValue(
						view,
						(k * numberOfChannels + i) * this.outputSampleSize,
						floats[j * CHUNK_SIZE + k]!,
					);
				}
			}
		}

		if (shouldClose) {
			audioSample.close();
		}

		const meta: EncodedAudioChunkMetadata = {
			decoderConfig: {
				codec: this.encodingConfig.codec,
				numberOfChannels,
				sampleRate,
			},
		};

		for (let i = 0; i < outputs.length; i++) {
			const { frameCount, view } = outputs[i]!;
			const outputBuffer = view.buffer;
			const startFrame = i * CHUNK_SIZE;

			const packet = new EncodedPacket(
				new Uint8Array(outputBuffer),
				'key',
				timestamp + startFrame / sampleRate,
				frameCount / sampleRate,
			);

			this.encodingConfig.onEncodedPacket?.(packet, meta);
			await this.muxer!.addEncodedAudioPacket(this.source._connectedTrack!, packet, meta); // With backpressure
		}
	}

	private ensureEncoder(audioSample: AudioSample) {
		if (this.encoderInitialized) {
			return;
		}

		const encoderError = new Error();
		return this.ensureEncoderPromise = (async () => {
			const { numberOfChannels, sampleRate } = audioSample;

			const encoderConfig = buildAudioEncoderConfig({
				numberOfChannels,
				sampleRate,
				...this.encodingConfig,
			});
			this.encodingConfig.onEncoderConfig?.(encoderConfig);

			const MatchingCustomEncoder = customAudioEncoders.find(x => x.supports(
				this.encodingConfig.codec,
				encoderConfig,
			));

			if (MatchingCustomEncoder) {
				// @ts-expect-error "Can't create instance of abstract class 🤓"
				this.customEncoder = new MatchingCustomEncoder() as CustomAudioEncoder;
				// @ts-expect-error It's technically readonly
				this.customEncoder.codec = this.encodingConfig.codec;
				// @ts-expect-error It's technically readonly
				this.customEncoder.config = encoderConfig;
				// @ts-expect-error It's technically readonly
				this.customEncoder.onPacket = (packet, meta) => {
					if (!(packet instanceof EncodedPacket)) {
						throw new TypeError('The first argument passed to onPacket must be an EncodedPacket.');
					}
					if (meta !== undefined && (!meta || typeof meta !== 'object')) {
						throw new TypeError('The second argument passed to onPacket must be an object or undefined.');
					}

					this.encodingConfig.onEncodedPacket?.(packet, meta);
					void this.muxer!.addEncodedAudioPacket(this.source._connectedTrack!, packet, meta);
				};

				await this.customEncoder.init();
			} else if ((PCM_AUDIO_CODECS as readonly string[]).includes(this.encodingConfig.codec)) {
				this.initPcmEncoder();
			} else {
				if (typeof AudioEncoder === 'undefined') {
					throw new Error('AudioEncoder is not supported by this browser.');
				}

				const support = await AudioEncoder.isConfigSupported(encoderConfig);
				if (!support.supported) {
					throw new Error(
						`This specific encoder configuration (${encoderConfig.codec}, ${encoderConfig.bitrate} bps,`
						+ ` ${encoderConfig.numberOfChannels} channels, ${encoderConfig.sampleRate} Hz) is not`
						+ ` supported by this browser. Consider using another codec or changing your audio parameters.`,
					);
				}

				this.encoder = new AudioEncoder({
					output: (chunk, meta) => {
						const packet = EncodedPacket.fromEncodedChunk(chunk);

						this.encodingConfig.onEncodedPacket?.(packet, meta);
						void this.muxer!.addEncodedAudioPacket(this.source._connectedTrack!, packet, meta);
					},
					error: (error) => {
						error.stack = encoderError.stack; // Provide a more useful stack trace
						this.encoderError ??= error;
					},
				});
				this.encoder.configure(encoderConfig);
			}

			assert(this.source._connectedTrack);
			this.muxer = this.source._connectedTrack.output._muxer;

			this.encoderInitialized = true;
		})();
	}

	private initPcmEncoder() {
		this.isPcmEncoder = true;

		const codec = this.encodingConfig.codec as PcmAudioCodec;
		const { dataType, sampleSize, littleEndian } = parsePcmCodec(codec);

		this.outputSampleSize = sampleSize;

		// All these functions receive a float sample as input and map it into the desired format

		switch (sampleSize) {
			case 1: {
				if (dataType === 'unsigned') {
					this.writeOutputValue = (view, byteOffset, value) =>
						view.setUint8(byteOffset, clamp((value + 1) * 127.5, 0, 255));
				} else if (dataType === 'signed') {
					this.writeOutputValue = (view, byteOffset, value) => {
						view.setInt8(byteOffset, clamp(Math.round(value * 128), -128, 127));
					};
				} else if (dataType === 'ulaw') {
					this.writeOutputValue = (view, byteOffset, value) => {
						const int16 = clamp(Math.floor(value * 32767), -32768, 32767);
						view.setUint8(byteOffset, toUlaw(int16));
					};
				} else if (dataType === 'alaw') {
					this.writeOutputValue = (view, byteOffset, value) => {
						const int16 = clamp(Math.floor(value * 32767), -32768, 32767);
						view.setUint8(byteOffset, toAlaw(int16));
					};
				} else {
					assert(false);
				}
			}; break;
			case 2: {
				if (dataType === 'unsigned') {
					this.writeOutputValue = (view, byteOffset, value) =>
						view.setUint16(byteOffset, clamp((value + 1) * 32767.5, 0, 65535), littleEndian);
				} else if (dataType === 'signed') {
					this.writeOutputValue = (view, byteOffset, value) =>
						view.setInt16(byteOffset, clamp(Math.round(value * 32767), -32768, 32767), littleEndian);
				} else {
					assert(false);
				}
			}; break;
			case 3: {
				if (dataType === 'unsigned') {
					this.writeOutputValue = (view, byteOffset, value) =>
						setUint24(view, byteOffset, clamp((value + 1) * 8388607.5, 0, 16777215), littleEndian);
				} else if (dataType === 'signed') {
					this.writeOutputValue = (view, byteOffset, value) =>
						setInt24(
							view,
							byteOffset,
							clamp(Math.round(value * 8388607), -8388608, 8388607),
							littleEndian,
						);
				} else {
					assert(false);
				}
			}; break;
			case 4: {
				if (dataType === 'unsigned') {
					this.writeOutputValue = (view, byteOffset, value) =>
						view.setUint32(byteOffset, clamp((value + 1) * 2147483647.5, 0, 4294967295), littleEndian);
				} else if (dataType === 'signed') {
					this.writeOutputValue = (view, byteOffset, value) =>
						view.setInt32(
							byteOffset,
							clamp(Math.round(value * 2147483647), -2147483648, 2147483647),
							littleEndian,
						);
				} else if (dataType === 'float') {
					this.writeOutputValue = (view, byteOffset, value) =>
						view.setFloat32(byteOffset, value, littleEndian);
				} else {
					assert(false);
				}
			}; break;
			case 8: {
				if (dataType === 'float') {
					this.writeOutputValue = (view, byteOffset, value) =>
						view.setFloat64(byteOffset, value, littleEndian);
				} else {
					assert(false);
				}
			}; break;
			default: {
				assertNever(sampleSize);
				assert(false);
			};
		}
	}

	async flushAndClose(forceClose: boolean) {
		if (!forceClose) this.checkForEncoderError();

		if (this.customEncoder) {
			if (!forceClose) {
				void this.customEncoderCallSerializer.call(() => this.customEncoder!.flush());
			}

			await this.customEncoderCallSerializer.call(() => this.customEncoder!.close());
		} else if (this.encoder) {
			if (!forceClose) {
				await this.encoder.flush();
			}

			if (this.encoder.state !== 'closed') {
				this.encoder.close();
			}
		}

		if (!forceClose) this.checkForEncoderError();
	}

	getQueueSize() {
		if (this.customEncoder) {
			return this.customEncoderQueueSize;
		} else if (this.isPcmEncoder) {
			return 0;
		} else {
			return this.encoder?.encodeQueueSize ?? 0;
		}
	}

	checkForEncoderError() {
		if (this.encoderError) {
			this.encoderError.stack = new Error().stack; // Provide an even more useful stack trace
			throw this.encoderError;
		}
	}
}

/**
 * This source can be used to add raw, unencoded audio samples to an output audio track. These samples will
 * automatically be encoded and then piped into the output.
 * @group Media sources
 * @public
 */
export class AudioSampleSource extends AudioSource {
	/** @internal */
	private _encoder: AudioEncoderWrapper;

	/**
	 * Creates a new {@link AudioSampleSource} whose samples are encoded according to the specified
	 * {@link AudioEncodingConfig}.
	 */
	constructor(encodingConfig: AudioEncodingConfig) {
		validateAudioEncodingConfig(encodingConfig);

		super(encodingConfig.codec);
		this._encoder = new AudioEncoderWrapper(this, encodingConfig);
	}

	/**
	 * Encodes an audio sample and then adds it to the output.
	 *
	 * @returns A Promise that resolves once the output is ready to receive more samples. You should await this Promise
	 * to respect writer and encoder backpressure.
	 */
	add(audioSample: AudioSample) {
		if (!(audioSample instanceof AudioSample)) {
			throw new TypeError('audioSample must be an AudioSample.');
		}

		return this._encoder.add(audioSample, false);
	}

	/** @internal */
	override _flushAndClose(forceClose: boolean) {
		return this._encoder.flushAndClose(forceClose);
	}
}

/**
 * This source can be used to add audio data from an AudioBuffer to the output track. This is useful when working with
 * the Web Audio API.
 * @group Media sources
 * @public
 */
export class AudioBufferSource extends AudioSource {
	/** @internal */
	private _encoder: AudioEncoderWrapper;
	/** @internal */
	private _accumulatedTime = 0;

	/**
	 * Creates a new {@link AudioBufferSource} whose `AudioBuffer` instances are encoded according to the specified
	 * {@link AudioEncodingConfig}.
	 */
	constructor(encodingConfig: AudioEncodingConfig) {
		validateAudioEncodingConfig(encodingConfig);

		super(encodingConfig.codec);
		this._encoder = new AudioEncoderWrapper(this, encodingConfig);
	}

	/**
	 * Converts an AudioBuffer to audio samples, encodes them and adds them to the output. The first AudioBuffer will
	 * be played at timestamp 0, and any subsequent AudioBuffer will have a timestamp equal to the total duration of
	 * all previous AudioBuffers.
	 *
	 * @returns A Promise that resolves once the output is ready to receive more samples. You should await this Promise
	 * to respect writer and encoder backpressure.
	 */
	async add(audioBuffer: AudioBuffer) {
		if (!(audioBuffer instanceof AudioBuffer)) {
			throw new TypeError('audioBuffer must be an AudioBuffer.');
		}

		const iterator = AudioSample._fromAudioBuffer(audioBuffer, this._accumulatedTime);
		this._accumulatedTime += audioBuffer.duration;

		for (const audioSample of iterator) {
			await this._encoder.add(audioSample, true);
		}
	}

	/** @internal */
	override _flushAndClose(forceClose: boolean) {
		return this._encoder.flushAndClose(forceClose);
	}
}

/**
 * Audio source that encodes the data of a
 * [`MediaStreamAudioTrack`](https://developer.mozilla.org/en-US/docs/Web/API/MediaStreamTrack) and pipes it into the
 * output. This is useful for capturing live or real-time audio such as microphones or audio from other media elements.
 * Audio will automatically start being captured once the connected {@link Output} is started, and will keep being
 * captured until the {@link Output} is finalized or this source is closed.
 * @group Media sources
 * @public
 */
export class MediaStreamAudioTrackSource extends AudioSource {
	/** @internal */
	private _encoder: AudioEncoderWrapper;
	/** @internal */
	private _abortController: AbortController | null = null;
	/** @internal */
	private _track: MediaStreamAudioTrack;
	/** @internal */
	private _audioContext: AudioContext | null = null;
	/** @internal */
	private _scriptProcessorNode: ScriptProcessorNode | null = null; // Deprecated but goated
	/** @internal */
	private _promiseWithResolvers = promiseWithResolvers();
	/** @internal */
	private _errorPromiseAccessed = false;

	/** A promise that rejects upon any error within this source. This promise never resolves. */
	get errorPromise() {
		this._errorPromiseAccessed = true;
		return this._promiseWithResolvers.promise;
	}

	/**
	 * Creates a new {@link MediaStreamAudioTrackSource} from a `MediaStreamAudioTrack`, which will pull audio samples
	 * from the stream in real time and encode them according to {@link AudioEncodingConfig}.
	 */
	constructor(track: MediaStreamAudioTrack, encodingConfig: AudioEncodingConfig) {
		if (!(track instanceof MediaStreamTrack) || track.kind !== 'audio') {
			throw new TypeError('track must be an audio MediaStreamTrack.');
		}
		validateAudioEncodingConfig(encodingConfig);

		super(encodingConfig.codec);
		this._encoder = new AudioEncoderWrapper(this, encodingConfig);
		this._track = track;
	}

	/** @internal */
	override async _start() {
		if (!this._errorPromiseAccessed) {
			console.warn(
				'Make sure not to ignore the `errorPromise` field on MediaStreamVideoTrackSource, so that any internal'
				+ ' errors get bubbled up properly.',
			);
		}

		this._abortController = new AbortController();

		if (typeof MediaStreamTrackProcessor !== 'undefined') {
			// Great, MediaStreamTrackProcessor is supported, this is the preferred way of doing things
			let firstAudioDataTimestamp: number | null = null;

			const processor = new MediaStreamTrackProcessor({ track: this._track });
			const consumer = new WritableStream<AudioData>({
				write: (audioData) => {
					if (firstAudioDataTimestamp === null) {
						firstAudioDataTimestamp = audioData.timestamp / 1e6;

						const muxer = this._connectedTrack!.output._muxer;
						if (muxer.firstMediaStreamTimestamp === null) {
							muxer.firstMediaStreamTimestamp = performance.now() / 1000;
							this._timestampOffset = -firstAudioDataTimestamp;
						} else {
							this._timestampOffset = (performance.now() / 1000 - muxer.firstMediaStreamTimestamp)
								- firstAudioDataTimestamp;
						}
					}

					if (this._encoder.getQueueSize() >= 4) {
						// Drop data if the encoder is overloaded
						audioData.close();
						return;
					}

					void this._encoder.add(new AudioSample(audioData), true)
						.catch((error) => {
							this._abortController?.abort();
							this._promiseWithResolvers.reject(error);
						});
				},
			});

			processor.readable.pipeTo(consumer, {
				signal: this._abortController.signal,
			}).catch((error) => {
				// Handle AbortError silently
				if (error instanceof DOMException && error.name === 'AbortError') return;

				this._promiseWithResolvers.reject(error);
			});
		} else {
			// Let's fall back to an AudioContext approach

			// eslint-disable-next-line @typescript-eslint/no-explicit-any, @typescript-eslint/no-unsafe-member-access
			const AudioContext = window.AudioContext || (window as any).webkitAudioContext;

			this._audioContext = new AudioContext({ sampleRate: this._track.getSettings().sampleRate });
			const sourceNode = this._audioContext.createMediaStreamSource(new MediaStream([this._track]));
			this._scriptProcessorNode = this._audioContext.createScriptProcessor(4096);

			if (this._audioContext.state === 'suspended') {
				await this._audioContext.resume();
			}

			sourceNode.connect(this._scriptProcessorNode);
			this._scriptProcessorNode.connect(this._audioContext.destination);

			let audioReceived = false;
			let totalDuration = 0;

			this._scriptProcessorNode.onaudioprocess = (event) => {
				const iterator = AudioSample._fromAudioBuffer(event.inputBuffer, totalDuration);
				totalDuration += event.inputBuffer.duration;

				for (const audioSample of iterator) {
					if (!audioReceived) {
						audioReceived = true;

						const muxer = this._connectedTrack!.output._muxer;
						if (muxer.firstMediaStreamTimestamp === null) {
							muxer.firstMediaStreamTimestamp = performance.now() / 1000;
						} else {
							this._timestampOffset = performance.now() / 1000 - muxer.firstMediaStreamTimestamp;
						}
					}

					if (this._encoder.getQueueSize() >= 4) {
						// Drop data if the encoder is overloaded
						audioSample.close();
						continue;
					}

					void this._encoder.add(audioSample, true)
						.catch((error) => {
							void this._audioContext!.suspend();
							this._promiseWithResolvers.reject(error);
						});
				}
			};
		}
	}

	/** @internal */
	override async _flushAndClose(forceClose: boolean) {
		if (this._abortController) {
			this._abortController.abort();
			this._abortController = null;
		}

		if (this._audioContext) {
			assert(this._scriptProcessorNode);

			this._scriptProcessorNode.disconnect();
			await this._audioContext.suspend();
		}

		await this._encoder.flushAndClose(forceClose);
	}
}

// === MEDIA STREAM TRACK PROCESSOR WORKER ===

type MediaStreamTrackProcessorWorkerMessage = {
	type: 'support';
	supported: boolean;
} | {
	type: 'videoFrame';
	trackId: number;
	videoFrame: VideoFrame;
} | {
	type: 'trackStopped';
	trackId: number;
} | {
	type: 'error';
	trackId: number;
	error: Error;
};

type MediaStreamTrackProcessorControllerMessage = {
	type: 'videoTrack';
	trackId: number;
	track: MediaStreamVideoTrack;
} | {
	type: 'stopTrack';
	trackId: number;
};

const mediaStreamTrackProcessorWorkerCode = () => {
	const sendMessage = (message: MediaStreamTrackProcessorWorkerMessage, transfer?: Transferable[]) => {
		if (transfer) {
			self.postMessage(message, { transfer });
		} else {
			self.postMessage(message);
		}
	};

	// Immediately send a message to the main thread, letting them know of the support
	sendMessage({
		type: 'support',
		supported: typeof MediaStreamTrackProcessor !== 'undefined',
	});

	const abortControllers = new Map<number, AbortController>();
	const stoppedTracks = new Set<number>();

	self.addEventListener('message', (event) => {
		const message = event.data as MediaStreamTrackProcessorControllerMessage;

		switch (message.type) {
			case 'videoTrack': {
				const processor = new MediaStreamTrackProcessor({ track: message.track });
				const consumer = new WritableStream<VideoFrame>({
					write: (videoFrame) => {
						if (stoppedTracks.has(message.trackId)) {
							videoFrame.close();
							return;
						}

						// Send it to the main thread
						sendMessage({
							type: 'videoFrame',
							trackId: message.trackId,
							videoFrame,
						}, [videoFrame]);
					},
				});

				const abortController = new AbortController();
				abortControllers.set(message.trackId, abortController);

				processor.readable.pipeTo(consumer, {
					signal: abortController.signal,
				}).catch((error: Error) => {
					// Handle AbortError silently
					if (error instanceof DOMException && error.name === 'AbortError') return;

					sendMessage({
						type: 'error',
						trackId: message.trackId,
						error,
					});
				});
			}; break;

			case 'stopTrack': {
				const abortController = abortControllers.get(message.trackId);
				if (abortController) {
					abortController.abort();
					abortControllers.delete(message.trackId);
				}

				stoppedTracks.add(message.trackId);

				sendMessage({
					type: 'trackStopped',
					trackId: message.trackId,
				});
			}; break;

			default: assertNever(message);
		}
	});
};

let nextMediaStreamTrackProcessorWorkerId = 0;
let mediaStreamTrackProcessorWorker: Worker | null = null;

const initMediaStreamTrackProcessorWorker = () => {
	const blob = new Blob(
		[`(${mediaStreamTrackProcessorWorkerCode.toString()})()`],
		{ type: 'application/javascript' },
	);
	const url = URL.createObjectURL(blob);

	mediaStreamTrackProcessorWorker = new Worker(url);
};

let mediaStreamTrackProcessorIsSupportedInWorkerCache: boolean | null = null;
const mediaStreamTrackProcessorIsSupportedInWorker = async () => {
	if (mediaStreamTrackProcessorIsSupportedInWorkerCache !== null) {
		return mediaStreamTrackProcessorIsSupportedInWorkerCache;
	}

	if (!mediaStreamTrackProcessorWorker) {
		initMediaStreamTrackProcessorWorker();
	}

	return new Promise<boolean>((resolve) => {
		assert(mediaStreamTrackProcessorWorker);

		const listener = (event: MessageEvent) => {
			const message = event.data as MediaStreamTrackProcessorWorkerMessage;

			if (message.type === 'support') {
				mediaStreamTrackProcessorIsSupportedInWorkerCache = message.supported;
				mediaStreamTrackProcessorWorker!.removeEventListener('message', listener);

				resolve(message.supported);
			}
		};

		mediaStreamTrackProcessorWorker.addEventListener('message', listener);
	});
};

const sendMessageToMediaStreamTrackProcessorWorker = (
	message: MediaStreamTrackProcessorControllerMessage,
	transfer?: Transferable[],
) => {
	assert(mediaStreamTrackProcessorWorker);

	if (transfer) {
		mediaStreamTrackProcessorWorker.postMessage(message, transfer);
	} else {
		mediaStreamTrackProcessorWorker.postMessage(message);
	}
};

/**
 * Base class for subtitle sources - sources for subtitle tracks.
 * @group Media sources
 * @public
 */
export abstract class SubtitleSource extends MediaSource {
	/** @internal */
	override _connectedTrack: OutputSubtitleTrack | null = null;
	/** @internal */
	_codec: SubtitleCodec;

	/** Internal constructor. */
	constructor(codec: SubtitleCodec) {
		super();

		if (!SUBTITLE_CODECS.includes(codec)) {
			throw new TypeError(`Invalid subtitle codec '${codec}'. Must be one of: ${SUBTITLE_CODECS.join(', ')}.`);
		}

		this._codec = codec;
	}
}

/**
 * This source can be used to add subtitles from a subtitle text file.
 * @group Media sources
 * @public
 */
export class TextSubtitleSource extends SubtitleSource {
	/** @internal */
	private _parser: SubtitleParser;

	/** Creates a new {@link TextSubtitleSource} where added text chunks are in the specified `codec`. */
	constructor(codec: SubtitleCodec) {
		super(codec);

		this._parser = new SubtitleParser({
			codec,
			output: (cue, metadata) =>
				this._connectedTrack?.output._muxer.addSubtitleCue(this._connectedTrack, cue, metadata),
		});
	}

	/**
	 * Parses the subtitle text according to the specified codec and adds it to the output track. You don't have to
	 * add the entire subtitle file at once here; you can provide it in chunks.
	 *
	 * @returns A Promise that resolves once the output is ready to receive more samples. You should await this Promise
	 * to respect writer and encoder backpressure.
	 */
	add(text: string) {
		if (typeof text !== 'string') {
			throw new TypeError('text must be a string.');
		}

		this._ensureValidAdd();
		this._parser.parse(text);

		return this._connectedTrack!.output._muxer.mutex.currentPromise;
	}
}