mediabunny/src/conversion.ts

/*!
 * Copyright (c) 2026-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,
	MediaCodec,
	NON_PCM_AUDIO_CODECS,
	VIDEO_CODECS,
	VideoCodec,
} from './codec';
import {
	AudioEncodingConfig,
	getEncodableAudioCodecs,
	getFirstEncodableVideoCodec,
	Quality,
	resolveQuality,
	VideoEncodingConfig,
} from './encode';
import { Input } from './input';
import { InputAudioTrack, InputTrack, InputVideoTrack } from './input-track';
import { Logging } from './logging';
import {
	AudioSampleSink,
	EncodedPacketSink,
	VideoSampleSink,
} from './media-sink';
import {
	AudioSource,
	EncodedVideoPacketSource,
	EncodedAudioPacketSource,
	VideoSource,
	VideoSampleSource,
	AudioSampleSource,
} from './media-source';
import {
	assert,
	assertNever,
	ceilToMultipleOfTwo,
	clamp,
	isIso639Dash2LanguageCode,
	isNumber,
	MaybePromise,
	normalizeRotation,
	promiseWithResolvers,
	Rotation,
} from './misc';
import { Output, OutputTrackGroup } from './output';
import { Mp4OutputFormat } from './output-format';
import { EncodedPacket } from './packet';
import {
	AudioSample,
	clampCropRectangle,
	CropRectangle,
	getBytesPerSample,
	validateCropRectangle,
	VideoSample,
	VideoSampleResource,
} from './sample';
import { MetadataTags, validateMetadataTags } from './metadata';
import { NullTarget } from './target';

/**
 * The options for media file conversion.
 * @group Conversion
 * @public
 */
export type ConversionOptions = {
	/** The input file. */
	input: Input;
	/** The output file. */
	output: Output;

	/**
	 * Defines which input tracks are used for conversion. Defaults to `'all'` unless the input is an HLS input, in
	 * which case it defaults to `'primary'`.
	 *
	 * - `'all'`: All input tracks are eligible for conversion.
	 * - `'primary'`: Only the primary video and audio track from the input are eligible for conversion.
	 */
	tracks?: 'all' | 'primary';

	/**
	 * 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 {@link InputVideoTrack} as well as a number `n`,
	 * which is the 1-based index of the track in the list of all video tracks. Using `n` is deprecated, prefer the
	 * identical `track.number` instead.
	 *
	 * When passing an array of a function that returns an array, one output track per array element will be created,
	 * allowing for "fan-out". Useful for creating multiple variants from a single track, for example with different
	 * resolutions.
	 */
	video?: ConversionVideoOptions
		| ConversionVideoOptions[]
		| ((track: InputVideoTrack, n: number) => MaybePromise<
			ConversionVideoOptions | 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 {@link InputAudioTrack} as well as a number `n`,
	 * which is the 1-based index of the track in the list of all audio tracks. Using `n` is deprecated, prefer the
	 * identical `track.number` instead.
	 *
	 * When passing an array of a function that returns an array, one output track per array element will be created,
	 * allowing for "fan-out". Useful for creating multiple variants from a single track, for example with different
	 * bitrates.
	 */
	audio?: ConversionAudioOptions
		| ConversionAudioOptions[]
		| ((track: InputAudioTrack, n: number) => MaybePromise<
			ConversionAudioOptions | 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`.
		 * When omitted, defaults to the earliest start timestamp of the non-discarded tracks, or to 0, whichever
		 * is higher.
		 */
		start?: number;
		/**
		 * The time in the input file in seconds at which the output file should end. Must be greater than `start`.
		 * Defaults to the duration of the input when omitted.
		 */
		end?: number;
	};

	/**
	 * Options for controlling when media is copied directly without transcoding it. Set to `false` to always transcode.
	 * Defaults to `{}`, which will copy media whenever possible and otherwise transcode it while retaining precise
	 * timestamps.
	 */
	copy?: ConversionCopyOptions | false;

	/**
	 * An object or a callback that returns or resolves to an object containing the descriptive metadata tags that
	 * should be written to the output file. If a function is passed, it will be passed the tags of the input file as
	 * its first argument, allowing you to modify, augment or extend them.
	 *
	 * 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;

	/**
	 * Whether this conversion is composable, defaults to `false`. A non-composable conversion takes full ownership of
	 * the output: it requires a fresh output and controls its entire lifecycle, meaning it starts it, writes its
	 * metadata tags, and finalizes it.
	 *
	 * A composable conversion only adds tracks to the output and drives their media data; starting and finalizing
	 * the output is an outside responsibility. This is useful when only some output tracks should be driven by a
	 * conversion, and other are to be driven manually. Additionally, it can be used to have multiple conversions target
	 * the same output.
	 */
	composable?: boolean;
};

/**
 * Video-specific options.
 * @group Conversion
 * @public
 */
export type ConversionVideoOptions = {
	/** If `true`, all video tracks will be discarded and will not be present in the output. */
	discard?: boolean;
	/**
	 * The desired width of the output video in pixels, defaulting to the video's natural display width. If height
	 * is not set, it will be deduced automatically based on aspect ratio.
	 */
	width?: number;
	/**
	 * The desired height of the output video in pixels, defaulting to the video's natural display height. If width
	 * is not set, it will be deduced automatically based on aspect ratio.
	 */
	height?: number;
	/**
	 * The fitting algorithm in case both width and height are set, or if the input video changes its size over time.
	 *
	 * - `'fill'` will stretch the image to fill the entire box, potentially altering aspect ratio.
	 * - `'contain'` will contain the entire image within the box while preserving aspect ratio. This may lead to
	 * letterboxing.
	 * - `'cover'` will scale the image until the entire box is filled, while preserving aspect ratio.
	 */
	fit?: 'fill' | 'contain' | 'cover';
	/**
	 * The angle in degrees to rotate the input video by, clockwise. Rotation is applied before cropping and resizing.
	 * This rotation is _in addition to_ the natural rotation of the input video as specified in input file's metadata.
	 */
	rotate?: Rotation;
	/**
	 * Defaults to `true`. When enabled, Mediabunny will use the rotation metadata in the output file to perform video
	 * rotation whenever possible. Set this field to `false` if you want to ensure the output file does not make use of
	 * rotation metadata and that any rotation is baked into the video frames directly.
	 */
	allowRotationMetadata?: boolean;
	/**
	 * Specifies the rectangular region of the input video to crop to. The crop region will automatically be clamped to
	 * the dimensions of the input video track. Cropping is performed after rotation but before resizing.
	 */
	crop?: CropRectangle;
	/**
	 * The desired frame rate of the output video, in hertz. If not specified, the original input frame rate will
	 * be used (which may be variable).
	 */
	frameRate?: number;
	/** The desired output video codec. */
	codec?: VideoCodec;
	/** The desired quality of the output video. */
	quality?: Quality;
	/**
	 * The desired bitrate of the output video.
	 * @deprecated Use `quality` instead.
	 */
	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';
	/**
	 * The interval, in seconds, of how often frames are encoded as a key frame. The default is 5 seconds. Frequent key
	 * frames improve seeking behavior but increase file size. When using multiple video tracks, you should give them
	 * all the same key frame interval.
	 *
	 * Setting this fields forces a transcode.
	 */
	keyFrameInterval?: number;
	/**
	 * A hint that configures the hardware acceleration method used when transcoding. This is best left on
	 * `'no-preference'`, the default.
	 */
	hardwareAcceleration?: 'no-preference' | 'prefer-hardware' | 'prefer-software';
	/** When `true`, video will always be re-encoded instead of directly copying over the encoded packets. */
	forceTranscode?: boolean;
	/**
	 * Allows for custom user-defined processing of video frames, e.g. for applying overlays, color transformations, or
	 * timestamp modifications. Will be called for each input video sample after transformations and frame rate
	 * corrections.
	 *
	 * Must return a {@link VideoSample}, a {@link VideoSampleResource} or a `CanvasImageSource`, an array of them, or
	 * `null` for dropping the frame. When non-timestamped data is returned, the timestamp and duration from the source
	 * sample will be used. Rotation metadata of the returned sample will be ignored.
	 *
	 * This function can also be used to manually resize frames. When doing so, you should signal the post-process
	 * dimensions using the `processedWidth` and `processedHeight` fields, which enables the encoder to better know what
	 * to expect. If these fields aren't set, Mediabunny will assume you won't perform any resizing.
	 */
	process?: (sample: VideoSample) => MaybePromise<
		CanvasImageSource | VideoSample | VideoSampleResource
		| (CanvasImageSource | VideoSample | VideoSampleResource)[] | null
	>;
	/**
	 * An optional hint specifying the width of video samples returned by the `process` function, for better
	 * encoder configuration.
	 */
	processedWidth?: number;
	/**
	 * An optional hint specifying the height of video samples returned by the `process` function, for better
	 * encoder configuration.
	 */
	processedHeight?: number;
	/**
	 * Defines the group(s) the output track is a part of. For more, see {@link BaseTrackMetadata.group}.
	 *
	 * If left blank, tracks will internally be assigned to groups such that the output track pairability graph exactly
	 * matches the input track pairability graph.
	 */
	group?: OutputTrackGroup | OutputTrackGroup[];
};

/**
 * Audio-specific options.
 * @group Conversion
 * @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. */
	numberOfChannels?: number;
	/** The desired sample rate of the output audio, in hertz. */
	sampleRate?: number;
	/**
	 * The desired sample format (and therefore bit depth) of the audio samples before they are passed to the encoder.
	 * Can be used to control bit depth with certain output codecs such as FLAC.
	 *
	 * Setting this field forces audio transcoding.
	 */
	sampleFormat?: 'u8' | 's16' | 's32' | 'f32';
	/** The desired output audio codec. */
	codec?: AudioCodec;
	/** The desired quality of the output audio. */
	quality?: Quality;
	/**
	 * The desired bitrate of the output audio.
	 * @deprecated Use `quality` instead.
	 */
	bitrate?: number | Quality;
	/** When `true`, audio will always be re-encoded instead of directly copying over the encoded packets. */
	forceTranscode?: boolean;
	/**
	 * Allows for custom user-defined processing of audio samples, e.g. for applying audio effects, transformations, or
	 * timestamp modifications. Will be called for each input audio sample after remixing and resampling.
	 *
	 * Must return an {@link AudioSample}, an array of them, or `null` for dropping the sample.
	 *
	 * This function can also be used to manually perform remixing or resampling. When doing so, you should signal the
	 * post-process parameters using the `processedNumberOfChannels` and `processedSampleRate` fields, which enables the
	 * encoder to better know what to expect. If these fields aren't set, Mediabunny will assume you won't perform
	 * remixing or resampling.
	 */
	process?: (sample: AudioSample) => MaybePromise<
		AudioSample | AudioSample[] | null
	>;
	/**
	 * An optional hint specifying the channel count of audio samples returned by the `process` function, for better
	 * encoder configuration.
	 */
	processedNumberOfChannels?: number;
	/**
	 * An optional hint specifying the sample rate of audio samples returned by the `process` function, for better
	 * encoder configuration.
	 */
	processedSampleRate?: number;
	/**
	 * Defines the group(s) the output track is a part of. For more, see {@link BaseTrackMetadata.group}.
	 *
	 * If left blank, tracks will internally be assigned to groups such that the output track pairability graph exactly
	 * matches the input track pairability graph.
	 */
	group?: OutputTrackGroup | OutputTrackGroup[];
};

/**
 * Options for copying encoded media during conversion.
 * @group Conversion
 * @public
 */
export type ConversionCopyOptions = {
	/**
	 * Controls whether media copying is preferred or required. Defaults to `'preferred'`.
	 *
	 * - `'forced'`: Copy encoded media where possible and discard tracks that cannot possibly be copied.
	 * - `'preferred'`: Copy encoded media when possible, and transcode tracks that cannot be copied.
	 */
	mode?: 'forced' | 'preferred';
	/**
	 * The maximum absolute shift, in seconds, that may be applied to the media to be able to copy it into the output
	 * format. Defaults to `0`, which permits no additional shift. Set to `Infinity` to permit any shift.
	 *
	 * A shift of `0` gives you perfect _timeline sync_: output timestamps will match input timestamps exactly (only
	 * offset by the trim region). Any non-zero shift will break this property but will still, under all circumstances,
	 * maintain perfect cross-track and audio-video sync.
	 */
	shiftTolerance?: number;
	/**
	 * Controls which media region will be copied to satisfy the requested trim range. Defaults to `'expand'`.
	 *
	 * - `'expand'`: Include at least all media in the requested range. This may require expanding the media region due
	 * to key frames and packet boundaries, and thus may include media outside of your trim range. The region is always
	 * minimally expanded to satisfy the copy criteria.
	 * - `'shrink'`: Only include media that lies entirely within the requested trim range. This may require shrinking
	 * the media region due to key frames and packet boundaries, and thus may exclude media inside of your trim range.
	 * The region is always minimally shrunk to satisfy the copy criteria.
	 *
	 * Use `expand` if you don't want to lose any media; use `shrink` to never expose any media outside of the
	 * trim region.
	 */
	boundaryPolicy?: 'expand' | 'shrink';
};

const validateVideoOptions = (videoOptions: ConversionVideoOptions) => {
	if (!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(', ')}.`,
		);
	}
	// eslint-disable-next-line @typescript-eslint/no-deprecated
	const bitrate = videoOptions?.bitrate;
	if (videoOptions?.quality !== undefined && !(videoOptions.quality instanceof Quality)) {
		throw new TypeError('options.video.quality, when provided, must be a Quality.');
	}
	if (videoOptions?.quality !== undefined && bitrate !== undefined) {
		throw new TypeError('options.video.quality and options.video.bitrate cannot both be provided.');
	}
	if (bitrate !== undefined && !(bitrate instanceof Quality) && (!Number.isInteger(bitrate) || 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?.allowRotationMetadata !== undefined && typeof videoOptions.allowRotationMetadata !== 'boolean') {
		throw new TypeError('options.video.allowRotationMetadata, when provided, must be a boolean.');
	}
	if (videoOptions?.crop !== undefined) {
		validateCropRectangle(videoOptions.crop, 'options.video.');
	}
	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.');
	}
	if (videoOptions?.alpha !== undefined && !['discard', 'keep'].includes(videoOptions.alpha)) {
		throw new TypeError('options.video.alpha, when provided, must be either \'discard\' or \'keep\'.');
	}
	if (
		videoOptions?.keyFrameInterval !== undefined
		&& (!Number.isFinite(videoOptions.keyFrameInterval) || videoOptions.keyFrameInterval < 0)
	) {
		throw new TypeError('options.video.keyFrameInterval, when provided, must be a non-negative number.');
	}
	if (videoOptions?.process !== undefined && typeof videoOptions.process !== 'function') {
		throw new TypeError('options.video.process, when provided, must be a function.');
	}
	if (
		videoOptions?.processedWidth !== undefined
		&& (!Number.isInteger(videoOptions.processedWidth) || videoOptions.processedWidth <= 0)
	) {
		throw new TypeError('options.video.processedWidth, when provided, must be a positive integer.');
	}
	if (
		videoOptions?.processedHeight !== undefined
		&& (!Number.isInteger(videoOptions.processedHeight) || videoOptions.processedHeight <= 0)
	) {
		throw new TypeError('options.video.processedHeight, when provided, must be a positive integer.');
	}
	if (
		videoOptions?.hardwareAcceleration !== undefined
		&& !['no-preference', 'prefer-hardware', 'prefer-software'].includes(videoOptions.hardwareAcceleration)
	) {
		throw new TypeError(
			'options.video.hardwareAcceleration, when provided, must be \'no-preference\', \'prefer-hardware\' or'
			+ ' \'prefer-software\'.',
		);
	}
	if (
		videoOptions?.group !== undefined
		&& !(
			videoOptions.group instanceof OutputTrackGroup
			|| (Array.isArray(videoOptions.group) && videoOptions.group.every(x => x instanceof OutputTrackGroup))
		)
	) {
		throw new TypeError(
			'options.video.group, when provided, must be an OutputTrackGroup or an array of OutputTrackGroups.',
		);
	}
};

const validateAudioOptions = (audioOptions: ConversionAudioOptions) => {
	if (!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(', ')}.`,
		);
	}
	// eslint-disable-next-line @typescript-eslint/no-deprecated
	const bitrate = audioOptions?.bitrate;
	if (audioOptions?.quality !== undefined && !(audioOptions.quality instanceof Quality)) {
		throw new TypeError('options.audio.quality, when provided, must be a Quality.');
	}
	if (audioOptions?.quality !== undefined && bitrate !== undefined) {
		throw new TypeError('options.audio.quality and options.audio.bitrate cannot both be provided.');
	}
	if (bitrate !== undefined && !(bitrate instanceof Quality) && (!Number.isInteger(bitrate) || 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.');
	}
	if (
		audioOptions?.sampleFormat !== undefined
		&& !['u8', 's16', 's32', 'f32'].includes(audioOptions.sampleFormat)
	) {
		throw new TypeError('options.audio.sampleFormat, when provided, must be one of: u8, s16, s32, f32.');
	}
	if (audioOptions?.process !== undefined && typeof audioOptions.process !== 'function') {
		throw new TypeError('options.audio.process, when provided, must be a function.');
	}
	if (
		audioOptions?.processedNumberOfChannels !== undefined
		&& (!Number.isInteger(audioOptions.processedNumberOfChannels) || audioOptions.processedNumberOfChannels <= 0)
	) {
		throw new TypeError('options.audio.processedNumberOfChannels, when provided, must be a positive integer.');
	}
	if (
		audioOptions?.processedSampleRate !== undefined
		&& (!Number.isInteger(audioOptions.processedSampleRate) || audioOptions.processedSampleRate <= 0)
	) {
		throw new TypeError('options.audio.processedSampleRate, when provided, must be a positive integer.');
	}
	if (
		audioOptions?.group !== undefined
		&& !(
			audioOptions.group instanceof OutputTrackGroup
			|| (Array.isArray(audioOptions.group) && audioOptions.group.every(x => x instanceof OutputTrackGroup))
		)
	) {
		throw new TypeError(
			'options.audio.group, when provided, must be an OutputTrackGroup or an array of OutputTrackGroups.',
		);
	}
};

const FALLBACK_NUMBER_OF_CHANNELS = 2;
const FALLBACK_SAMPLE_RATE = 48000;

/**
 * An input track that was discarded (excluded) from a {@link Conversion} alongside the discard reason.
 * @group Conversion
 * @public
 */
export type DiscardedTrack = {
	/** The track that was discarded. */
	track: InputTrack;
	/**
	 * The reason for discarding the track.
	 *
	 * - `'discarded_by_user'`: You discarded this track by setting `discard: true`.
	 * - `'max_track_count_reached'`: The output had no more room for another track.
	 * - `'max_track_count_of_type_reached'`: The output had no more room for another track of this type, or the output
	 * doesn't support this track type at all.
	 * - `'unknown_source_codec'`: We don't know the codec of the input track and therefore don't know what to do
	 * with it.
	 * - `'undecodable_source_codec'`: The input track's codec is known, but we are unable to decode it.
	 * - `'no_encodable_target_codec'`: We can't find a codec that we are able to encode and that can be contained
	 * within the output format. This reason can be hit if the environment doesn't support the necessary encoders, or if
	 * you requested a codec that cannot be contained within the output format.
	 * - `'cannot_copy'`: {@link ConversionCopyOptions.mode} was set to `'forced'` but the track could not be copied
	 * with the given copy configuration because it would require a transcode instead.
	 */
	reason:
		| 'discarded_by_user'
		| 'max_track_count_reached'
		| 'max_track_count_of_type_reached'
		| 'unknown_source_codec'
		| 'undecodable_source_codec'
		| 'no_encodable_target_codec'
		| 'cannot_copy';
	/** The options that were provided for this track, or `{}` if none were provided. */
	trackOptions: ConversionVideoOptions | ConversionAudioOptions;
};

/**
 * Options for controlling a single call to {@link Conversion.execute}.
 * @group Conversion
 * @public
 */
export type ConversionExecuteOptions = {
	/**
	 * The timestamp in seconds, in the output's timescale, until which the conversion should advance. Defaults to
	 * `Infinity`, meaning the conversion runs until the end.
	 *
	 * This field is especially useful for composable conversions, as it allows you to advance the conversion in
	 * lockstep with other media data sources.
	 */
	until?: number;
	/**
	 * A signal that, when triggered, pauses the conversion as soon as possible.
	 */
	pauseSignal?: AbortSignal;
};

type TrackPump = {
	done: boolean;
	resolvers: ReturnType<typeof promiseWithResolvers<void>>;
	wake: (() => void) | null;
	start: () => void;
};

/**
 * Represents a media file conversion process, used to convert one media file into another. In addition to conversion,
 * this class can be used to resize and rotate video, resample audio, drop tracks, or trim to a specific time range.
 * @group Conversion
 * @public
 */
export class Conversion {
	/** The input file. */
	readonly input: Input;
	/** The output file. */
	readonly output: Output;

	/** @internal */
	_state: 'idle' | 'executing' | 'canceled' | 'done' = 'idle';
	/** @internal */
	_options: ConversionOptions;
	/** @internal */
	_copyMode: false | 'forced' | 'preferred';
	/** @internal */
	_copyTimestampShiftTolerance: number;
	/** @internal */
	_copyBoundaryPolicy: 'expand' | 'shrink';
	/** @internal */
	_startTimestamp!: number;
	/** @internal */
	_endTimestamp!: number;
	/** @internal */
	_timestampOffset = 0;
	/** @internal */
	_timestampOffsetAdjusted = false;
	/** @internal */
	_copyTimestampPossible = new Map<InputTrack, boolean>();
	/** @internal */
	_copyStartPackets = new Map<InputTrack, EncodedPacket | null>();

	/** @internal */
	_nextOutputTrackId = 0;
	/** @internal */
	_outputTrackIds: number[] = [];
	/** @internal */
	_outputOwnTrackGroups: (OutputTrackGroup | null)[] = [];

	/** @internal */
	_trackPumps: TrackPump[] = [];
	/** @internal */
	_composable = false;

	/** @internal */
	_executed = false;
	/** @internal */
	_executionUntil = Infinity;
	/** @internal */
	_pauseRequested = false;

	/** @internal */
	_synchronizer = new TrackSynchronizer(this);

	/** @internal */
	_totalDuration: number | null = null;
	/** @internal */
	_maxTimestamps = new Map<number, number>(); // Track ID -> timestamp

	/**
	 * A callback that is fired whenever the conversion progresses. Gets passed as first argument a number between
	 * 0 and 1, indicating the completion of the conversion. Note that a progress of 1 doesn't necessarily mean the
	 * conversion is complete; the conversion is complete once `execute()` resolves.
	 *
	 * As second argument, this callback receives the input time in seconds that has been processed.
	 *
	 * In order for progress to be computed, this property must be set before `execute` is called.
	 */
	onProgress?: (progress: number, processedTime: number) => unknown = undefined;
	/** @internal */
	_computeProgress = false;
	/** @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. Composable conversions are always valid, even if they utilize
	 * zero tracks.
	 *
	 * Note: a conversion having discarded tracks does not automatically mean it is invalid; if the remaining, utilized
	 * tracks make for a valid output file, the conversion is still allowed.
	 */
	isValid = false;
	/**
	 * The list of tracks that are included in the output file. When fan-out is used, the same track appears in this
	 * array multiple times.
	 */
	readonly utilizedTracks: InputTrack[] = [];
	/** The list of tracks from the input file that have been discarded, alongside the discard reason. */
	readonly discardedTracks: DiscardedTrack[] = [];

	/**
	 * The current state of the conversion.
	 *
	 * - `'idle'`: The conversion is not currently executing and isn't done; `execute` can be called.
	 * - `'executing'`: A call to `execute` is currently running.
	 * - `'canceled'`: The conversion has been canceled and can no longer be executed.
	 * - `'done'`: The conversion has run to completion. Subsequent calls to `execute` do nothing.
	 */
	get state() {
		return this._state;
	}

	/** Initializes a new conversion process without starting the conversion. */
	static async init(options: ConversionOptions) {
		const conversion = new Conversion(options);
		await conversion._init();

		return conversion;
	}

	/** Creates a new Conversion instance (duh). */
	private constructor(options: ConversionOptions) {
		if (!options || typeof options !== 'object') {
			throw new TypeError('options must be an object.');
		}
		if (!(options.input instanceof Input)) {
			throw new TypeError('options.input must be an Input.');
		}
		if (!(options.output instanceof Output)) {
			throw new TypeError('options.output must be an Output.');
		}
		if (
			options.tracks !== undefined
			&& options.tracks !== 'all'
			&& options.tracks !== 'primary'
		) {
			throw new TypeError(
				'options.tracks, when provided, must be either \'all\' or \'primary\'.',
			);
		}
		if (options.composable !== undefined && typeof options.composable !== 'boolean') {
			throw new TypeError('options.composable, when provided, must be a boolean.');
		}
		if (options.copy !== undefined && options.copy !== false) {
			if (!options.copy || typeof options.copy !== 'object') {
				throw new TypeError('options.copy, when provided, must be an object or false.');
			}
			if (options.copy.mode !== undefined && !['forced', 'preferred'].includes(options.copy.mode)) {
				throw new TypeError('options.copy.mode, when provided, must be \'forced\' or \'preferred\'.');
			}
			if (
				options.copy.shiftTolerance !== undefined
				&& (!isNumber(options.copy.shiftTolerance) || options.copy.shiftTolerance < 0)
			) {
				throw new TypeError('options.copy.shiftTolerance, when provided, must be a non-negative number.');
			}
			if (
				options.copy.boundaryPolicy !== undefined
				&& !['expand', 'shrink'].includes(options.copy.boundaryPolicy)
			) {
				throw new TypeError(
					'options.copy.boundaryPolicy, when provided, must be \'expand\' or \'shrink\'.',
				);
			}
		}

		const composable = options.composable ?? false;
		if (!composable) {
			if (
				options.output.tracks.length > 0
				|| Object.keys(options.output._metadataTags).length > 0
				|| options.output.state !== 'pending'
			) {
				throw new TypeError('options.output must be fresh: no tracks or metadata tags added and not started.');
			}
		} else {
			if (options.tags !== undefined) {
				throw new TypeError(
					'options.tags cannot be set by a composable conversion; set metadata directly on the output'
					+ ' instead.',
				);
			}

			if (options.output.state !== 'pending') {
				throw new TypeError('options.output must not have been started yet.');
			}
		}

		if (options.video !== undefined && typeof options.video !== 'function') {
			if (Array.isArray(options.video)) {
				for (const obj of options.video) {
					validateVideoOptions(obj);
				}
			} else {
				validateVideoOptions(options.video);
			}
		} else {
			// We'll validate the return value later
		}

		if (options.audio !== undefined && typeof options.audio !== 'function') {
			if (Array.isArray(options.audio)) {
				for (const obj of options.audio) {
					validateAudioOptions(obj);
				}
			} else {
				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.');
		}
		if (options.trim?.start !== undefined && (!Number.isFinite(options.trim.start))) {
			throw new TypeError('options.trim.start, when provided, must be a finite number.');
		}
		if (options.trim?.end !== undefined && (!isNumber(options.trim.end))) {
			throw new TypeError('options.trim.end, when provided, must be a number.');
		}
		if (
			options.trim?.start !== undefined
			&& options.trim.end !== undefined
			&& options.trim.start >= options.trim.end) {
			throw new TypeError('options.trim.start must be less than options.trim.end.');
		}
		if (
			options.tags !== undefined
			&& (typeof options.tags !== 'object' || !options.tags)
			&& typeof options.tags !== 'function'
		) {
			throw new TypeError('options.tags, when provided, must be an object or a function.');
		}
		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._copyMode = options.copy === false ? false : options.copy?.mode ?? 'preferred';
		this._copyTimestampShiftTolerance = options.copy === false ? 0 : options.copy?.shiftTolerance ?? 0;
		this._copyBoundaryPolicy = options.copy === false ? 'expand' : options.copy?.boundaryPolicy ?? 'expand';
		this._composable = composable;
		this.input = options.input;
		this.output = options.output;
	}

	/** @internal */
	async _init() {
		const inputFormat = await this.input.getFormat();

		let tracks: InputTrack[];

		let trackMode = this._options.tracks;
		if (trackMode === undefined) {
			// HACK to keep bundle size low, temp for now
			const defaultTrackMode = inputFormat.name.includes('(HLS)')
				? 'primary'
				: 'all';

			trackMode = defaultTrackMode;
		}

		if (trackMode === 'all') {
			tracks = await this.input.getTracks();
		} else if (trackMode === 'primary') {
			const primaryVideoTrack = await this.input.getPrimaryVideoTrack();
			const primaryAudioTrack = await this.input.getPrimaryAudioTrack();

			tracks = [primaryVideoTrack, primaryAudioTrack].filter(x => x !== null);
		} else {
			assertNever(trackMode);
			assert(false);
		}

		const outputTrackCounts = this.output.format.getSupportedTrackCounts();

		// Input track counters
		let nVideo = 1;
		let nAudio = 1;

		// All tracks that aren't discarded by the user
		const filteredTracks: InputTrack[] = [];
		const filteredTrackOptions: (ConversionVideoOptions | ConversionAudioOptions)[][] = [];

		for (const track of tracks) {
			let trackOptions: (ConversionVideoOptions | ConversionAudioOptions)[];

			if (track.isVideoTrack()) {
				if (this._options.video) {
					if (typeof this._options.video === 'function') {
						const returnedTrackOptions = await this._options.video(track, nVideo) ?? {};
						if (Array.isArray(returnedTrackOptions)) {
							for (const obj of returnedTrackOptions) {
								validateVideoOptions(obj);
							}
						} else {
							validateVideoOptions(returnedTrackOptions);
						}

						trackOptions = Array.isArray(returnedTrackOptions)
							? returnedTrackOptions
							: [returnedTrackOptions];

						nVideo++;
					} else {
						// Already validated
						trackOptions = Array.isArray(this._options.video)
							? this._options.video
							: [this._options.video];
					}
				} else {
					trackOptions = [{}];
				}
			} else if (track.isAudioTrack()) {
				if (this._options.audio) {
					if (typeof this._options.audio === 'function') {
						const returnedTrackOptions = await this._options.audio(track, nAudio) ?? {};
						if (Array.isArray(returnedTrackOptions)) {
							for (const obj of returnedTrackOptions) {
								validateAudioOptions(obj);
							}
						} else {
							validateAudioOptions(returnedTrackOptions);
						}

						trackOptions = Array.isArray(returnedTrackOptions)
							? returnedTrackOptions
							: [returnedTrackOptions];

						nAudio++;
					} else {
						// Already validated
						trackOptions = Array.isArray(this._options.audio)
							? this._options.audio
							: [this._options.audio];
					}
				} else {
					trackOptions = [{}];
				}
			} else {
				assert(false);
			}

			const discardOptions = trackOptions.filter(x => x.discard);
			for (const discardOption of discardOptions) {
				this.discardedTracks.push({
					track,
					reason: 'discarded_by_user',
					trackOptions: discardOption,
				});
			}

			if (trackOptions.length === discardOptions.length) {
				if (trackOptions.length === 0) {
					this.discardedTracks.push({
						track,
						reason: 'discarded_by_user',
						trackOptions: {},
					});
				}

				continue;
			}

			const nonDiscardOptions = trackOptions.filter(x => !x.discard);
			filteredTracks.push(track);
			filteredTrackOptions.push(nonDiscardOptions);
		}

		if (this._options.trim?.start !== undefined) {
			this._startTimestamp = this._options.trim.start;
		} else {
			// Compute the start timestamp from the set of filtered tracks. Technically these can still be narrowed
			// down later due to discarded tracks, but we need to fix the start timestamp now due to track processing
			// depending on it.
			this._startTimestamp = Math.max(
				await this.input.getFirstTimestamp(filteredTracks),
				// Samples can also have negative timestamps, but the meaning typically is "don't present me", so let's
				// cut those out by default.
				0,
			);
		}

		this._endTimestamp = Math.max(this._options.trim?.end ?? Infinity, this._startTimestamp);
		this._timestampOffset = -this._startTimestamp; // Initial value, may get refined later by track processing

		// Run these sequentially so that output tracks have a deterministic order
		for (let i = 0; i < filteredTracks.length; i++) {
			const track = filteredTracks[i]!;
			const options = filteredTrackOptions[i]!;

			for (const option of options) {
				if (this.output.tracks.length === outputTrackCounts.total.max) {
					this.discardedTracks.push({
						track,
						reason: 'max_track_count_reached',
						trackOptions: option,
					});
					continue;
				}

				const addedCountOfType = this.output.tracks.reduce(
					(count, t) => count + (t.type === track.type ? 1 : 0),
					0,
				);

				if (addedCountOfType === outputTrackCounts[track.type].max) {
					this.discardedTracks.push({
						track,
						reason: 'max_track_count_of_type_reached',
						trackOptions: option,
					});
					continue;
				}

				const outputTrackId = this._nextOutputTrackId++;

				if (track.isVideoTrack()) {
					await this._processVideoTrack(track, option as ConversionVideoOptions, outputTrackId);
				} else if (track.isAudioTrack()) {
					await this._processAudioTrack(track, option as ConversionAudioOptions, outputTrackId);
				} else {
					assert(false);
				}
			}
		}

		// When no track groups are set by the user, then the output track pairability should be *identical* to the
		// input's. We do the naive algorithm to achieve this: assign each track to its own group, and pair groups with
		// each other based on input track pairability.
		for (let i = 0; i < this.utilizedTracks.length - 1; i++) {
			for (let j = i + 1; j < this.utilizedTracks.length; j++) {
				const trackA = this.utilizedTracks[i]!;
				const trackB = this.utilizedTracks[j]!;
				const ownGroupA = this._outputOwnTrackGroups[i];
				const ownGroupB = this._outputOwnTrackGroups[j];

				assert(ownGroupA !== undefined);
				assert(ownGroupB !== undefined);

				if (ownGroupA && ownGroupB && trackA.canBePairedWith(trackB)) {
					ownGroupA.pairWith(ownGroupB);
				}
			}
		}

		// Now, let's deal with metadata tags. A composable conversion does not touch the output's metadata tags; that
		// remains the responsibility of whoever owns the output.

		if (!this._composable) {
			const inputTags = await this.input.getMetadataTags();
			let outputTags: MetadataTags;

			if (this._options.tags) {
				const result = typeof this._options.tags === 'function'
					? await this._options.tags(inputTags)
					: this._options.tags;
				validateMetadataTags(result);

				outputTags = result;
			} else {
				outputTags = inputTags;
			}

			// Somewhat dirty but pragmatic
			const inputAndOutputFormatMatch = inputFormat.mimeType === this.output.format.mimeType;
			const rawTagsAreUnchanged = inputTags.raw === outputTags.raw;

			if (inputTags.raw && rawTagsAreUnchanged && !inputAndOutputFormatMatch) {
				// If the input and output formats aren't the same, copying over raw metadata tags makes no sense and
				// only results in junk tags, so let's cut them out.
				delete outputTags.raw;
			}

			this.output.setMetadataTags(outputTags);
		}

		// Let's check if the conversion can actually be executed
		if (!this._composable) {
			this.isValid = this.output.hasEnoughTracks() && this.output.tracks.length > 0;
		} else {
			// Checking Output start validity is not up to us. We even consider zero-track conversions to be valid
			this.isValid = true;
		}

		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) {
				if (warnElements.length > 0) {
					warnElements.push('\n\n');
				}

				warnElements.push(this._getInvalidityExplanation().join(''));
			}

			if (warnElements.length > 0) {
				Logging._warn(...warnElements);
			}
		}
	}

	/** @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',
			) && this.discardedTracks.some(x => 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 [];

					let supportedCodecs: MediaCodec[];
					if (x.track.type === 'video') {
						supportedCodecs = this.output.format.getSupportedVideoCodecs();
					} else if (x.track.type === 'audio') {
						supportedCodecs = this.output.format.getSupportedAudioCodecs();
					} else {
						supportedCodecs = this.output.format.getSupportedSubtitleCodecs();
					}

					// If the user requested a specific codec, only that codec was ever attempted
					return supportedCodecs.filter(codec => !x.trackOptions.codec || codec === x.trackOptions.codec);
				});

				const uniqueCodecs = [...new Set(codecs)];

				if (uniqueCodecs.length === 1) {
					elements.push(
						`\nTracks were discarded because your environment is not able to encode '${uniqueCodecs[0]}'`
						+ ' with the provided parameters.',
					);
				} else {
					elements.push(
						'\nTracks were discarded because your environment is not able to encode any of the codecs'
						+ ` ${uniqueCodecs.map(x => `'${x}'`).join(', ')} with the provided parameters.`,
					);
				}

				if (uniqueCodecs.includes('mp3')) {
					elements.push(
						`\nThe @mediabunny/mp3-encoder extension package provides support for encoding MP3.`,
					);
				}

				if (uniqueCodecs.includes('aac')) {
					elements.push(
						'\nThe @mediabunny/aac-encoder extension package provides support for encoding AAC.',
					);
				}

				if (uniqueCodecs.includes('ac3') || uniqueCodecs.includes('eac3')) {
					elements.push(
						'\nThe @mediabunny/ac3 extension package provides support'
						+ ' for encoding and decoding AC-3/E-AC-3.',
					);
				}

				if (uniqueCodecs.includes('flac')) {
					elements.push(
						'\nThe @mediabunny/flac-encoder extension package provides support for encoding FLAC.',
					);
				}
			} else {
				elements.push('\nCheck the discardedTracks field for more info.');
			}
		}

		return elements;
	}

	/**
	 * Executes the conversion process and resolves when the conversion is complete. When
	 * {@link ConversionExecuteOptions.until} is provided, the conversion will be suspended once that output timestamp
	 * is reached and can be resumed with another call to `execute`. An ongoing execution may also be suspended via
	 * {@link ConversionExecuteOptions.pauseSignal}.
	 *
	 * Execution will throw if `isValid` is `false`.
	 */
	async execute(options: ConversionExecuteOptions = {}) {
		if (!options || typeof options !== 'object') {
			throw new TypeError('options must be an object.');
		}
		if (options.until !== undefined && (typeof options.until !== 'number' || Number.isNaN(options.until))) {
			throw new TypeError('options.until, when provided, must be a number.');
		}
		if (options.pauseSignal !== undefined && !(options.pauseSignal instanceof AbortSignal)) {
			throw new TypeError('options.pauseSignal, when provided, must be an AbortSignal.');
		}

		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._state === 'executing') {
			throw new Error('Cannot call execute() while a previous call to execute() is still running.');
		}

		if (this._state === 'canceled') {
			throw new ConversionCanceledError();
		}

		if (this._state === 'done') {
			// The conversion already ran to completion, nothing left to do
			return;
		}

		if (this._composable && this.output.state === 'pending') {
			throw new Error(
				'A composable conversion requires the output to be started. Call start() on the output before executing'
				+ ' the conversion.',
			);
		}

		this._state = 'executing';
		this._executionUntil = options.until ?? Infinity;
		this._pauseRequested = options.pauseSignal?.aborted ?? false;

		const onPause = () => {
			if (this._state !== 'executing') {
				return;
			}

			this._pauseRequested = true;

			// Release any pumps stuck in the synchronizer so they can reach their next checkpoint and suspend
			this._synchronizer.resolveAll();
		};
		options.pauseSignal?.addEventListener('abort', onPause);

		for (const pump of this._trackPumps) {
			if (!pump.done) {
				pump.resolvers = promiseWithResolvers();
			}
		}

		if (!this._executed) {
			this._executed = true;

			for (const id of this._outputTrackIds) {
				this._synchronizer.declareTrack(id);
			}

			if (this.onProgress) {
				// Compute duration using only the utilized tracks
				const uniqueUtilizedTracks = new Set(this.utilizedTracks);
				const durationPromises = [...uniqueUtilizedTracks].map(async (track) => {
					if (await track.isLive()) {
						return Infinity; // Upper bound (assuming no universe heat death)
					}

					return (await track.getDurationFromMetadata()) ?? (await track.computeDuration());
				});
				const duration = Math.max(0, ...await Promise.all(durationPromises));

				this._computeProgress = true;
				this._totalDuration = Math.min(
					duration - this._startTimestamp,
					this._endTimestamp - this._startTimestamp,
				);

				for (const id of this._outputTrackIds) {
					// Used for progress calculation. We start these at 0 which is technically not always the first
					// timestamp, but this is how we choose to model what "progress" means: it's how far we are done
					// with the trim region.
					this._maxTimestamps.set(id, 0);
				}

				this.onProgress?.(0, 0);
			}

			if (!this._composable) {
				await this.output.start();
			}

			for (const pump of this._trackPumps) {
				pump.start();
			}
		} else {
			// Wake all suspended track pumps
			for (const pump of this._trackPumps) {
				pump.wake?.();
			}
		}

		try {
			await Promise.all(this._trackPumps.map(x => x.resolvers.promise));
		} catch (error) {
			if ((this._state as Conversion['_state']) !== 'canceled') {
				// Make sure to cancel to stop other encoding processes and clean up resources
				void this.cancel();
			}

			throw error;
		} finally {
			options.pauseSignal?.removeEventListener('abort', onPause);
		}

		if ((this._state as Conversion['_state']) === 'canceled') {
			throw new ConversionCanceledError();
		}

		const isDone = this._trackPumps.every(x => x.done);
		this._state = isDone ? 'done' : 'idle';

		if (isDone) {
			if (!this._composable) {
				await this.output.finalize();
			}

			if (this._computeProgress) {
				const minTimestamp = Math.min(...this._maxTimestamps.values());
				this.onProgress?.(1, minTimestamp);
			}
		}
	}

	/**
	 * Cancels the conversion process, causing any ongoing `execute` call to throw a `ConversionCanceledError`.
	 * Does nothing if the conversion is already complete.
	 */
	async cancel() {
		if (this._state === 'done') {
			return;
		}

		if (this._state === 'canceled') {
			Logging._warn('Conversion already canceled.');
			return;
		}

		this._state = 'canceled';

		// Wake all suspended track pumps so they can wind down
		for (const pump of this._trackPumps) {
			pump.wake?.();
		}

		this._synchronizer.resolveAll();

		if (!this._composable) {
			await this.output.cancel();
		}
	}

	/** @internal */
	async _processVideoTrack(track: InputVideoTrack, trackOptions: ConversionVideoOptions, outputTrackId: number) {
		const sourceCodec = await track.getCodec();
		if (!sourceCodec) {
			this.discardedTracks.push({
				track,
				reason: 'unknown_source_codec',
				trackOptions,
			});
			return;
		}

		let videoSource: VideoSource;

		const innateRotation = await track.getRotation();
		const totalRotation = normalizeRotation(innateRotation + (trackOptions.rotate ?? 0));
		let outputTrackRotation = totalRotation;
		const canUseRotationMetadata = this.output.format.supportsVideoRotationMetadata
			&& (trackOptions.allowRotationMetadata ?? true);

		const squarePixelWidth = await track.getSquarePixelWidth();
		const squarePixelHeight = await track.getSquarePixelHeight();
		const [rotatedWidth, rotatedHeight] = totalRotation % 180 === 0
			? [squarePixelWidth, squarePixelHeight]
			: [squarePixelHeight, squarePixelWidth];

		let crop = trackOptions.crop;
		if (crop) {
			crop = clampCropRectangle(crop, rotatedWidth, rotatedHeight);
		}

		const [originalWidth, originalHeight] = crop
			? [crop.width, crop.height]
			: [rotatedWidth, rotatedHeight];

		let width = originalWidth;
		let height = originalHeight;
		const aspectRatio = width / height;

		// A lot of video encoders require that the dimensions be multiples of 2
		if (trackOptions.width !== undefined && trackOptions.height === undefined) {
			width = ceilToMultipleOfTwo(trackOptions.width);
			height = ceilToMultipleOfTwo(Math.round(width / aspectRatio));
		} else if (trackOptions.width === undefined && trackOptions.height !== undefined) {
			height = ceilToMultipleOfTwo(trackOptions.height);
			width = ceilToMultipleOfTwo(Math.round(height * aspectRatio));
		} else if (trackOptions.width !== undefined && trackOptions.height !== undefined) {
			width = ceilToMultipleOfTwo(trackOptions.width);
			height = ceilToMultipleOfTwo(trackOptions.height);
		}

		let videoCodecs = this.output.format.getSupportedVideoCodecs();
		const alpha = trackOptions.alpha ?? 'discard';

		let needsTranscode = !this._copyMode
			|| !!trackOptions.forceTranscode
			|| !!trackOptions.frameRate
			|| trackOptions.keyFrameInterval !== undefined
			|| trackOptions.process !== undefined
			|| trackOptions.quality !== undefined
			// eslint-disable-next-line @typescript-eslint/no-deprecated
			|| trackOptions.bitrate !== undefined
			|| !videoCodecs.includes(sourceCodec)
			|| (trackOptions.codec && trackOptions.codec !== sourceCodec)
			|| width !== originalWidth
			|| height !== originalHeight
			// TODO This is suboptimal: Forcing a rerender when both rotation and process are set is not
			// performance-optimal, but right now there's no other way because we can't change the track rotation
			// metadata after the output has already started. Should be possible with API changes in v2, though!
			|| (totalRotation !== 0 && !canUseRotationMetadata)
			|| !!crop;

		let copyStartPacket: EncodedPacket | null = null;

		if (!needsTranscode) {
			// Check if we can copy it
			const sink = new EncodedPacketSink(track);
			let startPacket = await sink.getKeyPacket(this._startTimestamp, { verifyKeyPackets: true })
				?? await sink.getFirstKeyPacket({ verifyKeyPackets: true });

			if (
				startPacket
				&& startPacket.timestamp < this._startTimestamp
				&& startPacket.timestamp + startPacket.duration <= this._startTimestamp
				&& this._copyBoundaryPolicy === 'shrink'
			) {
				startPacket = await sink.getNextKeyPacket(startPacket, { verifyKeyPackets: true });
			}

			copyStartPacket = startPacket;

			if (startPacket) {
				// This clamp mirrors the packet timestamp clamping the copy loop does. The reason this is valid is
				// because in the shrink case, we've already proven that the packet (at least partially) overlaps the
				// trim region.
				const effectiveStartTimestamp = this._copyBoundaryPolicy === 'shrink'
					? Math.max(startPacket.timestamp, this._startTimestamp)
					: startPacket.timestamp;

				if (!this.output.format.supportsTimestampedMediaData) {
					// Wants zero

					if (this._timestampOffsetAdjusted) {
						// We've already adjusted, we can't adjust twice
						const isValid = effectiveStartTimestamp + this._timestampOffset === 0;
						if (!isValid) {
							needsTranscode = true;
						}
					} else {
						const correction = clamp(
							this._startTimestamp - effectiveStartTimestamp,
							-this._copyTimestampShiftTolerance,
							this._copyTimestampShiftTolerance,
						);

						const shiftedStartTimestamp = effectiveStartTimestamp + correction;
						const isValid = shiftedStartTimestamp === this._startTimestamp;

						if (isValid) {
							this._timestampOffset = -this._startTimestamp + correction;
							this._timestampOffsetAdjusted = true;
						} else {
							needsTranscode = true;
						}
					}
				} else if (
					this.output.format.negativeTimestampSupport !== 'full'
					&& effectiveStartTimestamp < this._startTimestamp
				) {
					const correction = Math.min(
						this._startTimestamp - effectiveStartTimestamp,
						this._copyTimestampShiftTolerance,
					);

					const shiftedStartTimestamp = effectiveStartTimestamp + correction;
					const isValid = shiftedStartTimestamp >= this._startTimestamp
						|| (
							this.output.format.negativeTimestampSupport === 'prefer-non-negative'
							&& this._copyMode === 'forced'
						);

					if (isValid) {
						this._timestampOffset = Math.max(this._timestampOffset, -this._startTimestamp + correction);
					} else {
						needsTranscode = true;
					}
				}
			}
		}

		if (needsTranscode && this._copyMode === 'forced') {
			this.discardedTracks.push({
				track,
				reason: 'cannot_copy',
				trackOptions,
			});
			return;
		}

		if (!needsTranscode) {
			// Fast path, we can simply copy over the encoded packets

			const source = new EncodedVideoPacketSource(sourceCodec);
			videoSource = source;

			this._registerTrackPump(async (pump) => {
				const sink = new EncodedPacketSink(track);
				const decoderConfig = await track.getDecoderConfig();
				const meta: EncodedVideoChunkMetadata = { decoderConfig: decoderConfig ?? undefined };

				// eslint-disable-next-line curly
				if (copyStartPacket) for await (const packet of sink.packets(
					copyStartPacket,
					undefined,
					{ verifyKeyPackets: true },
				)) {
					if (this._state === 'canceled') {
						break;
					}

					if (packet.timestamp >= this._endTimestamp) {
						if (this._copyBoundaryPolicy === 'shrink') {
							break;
						} else {
							// Due to B-frames, there might still be packets we care about later on. Do a short
							// lookahead to find out if there are.

							let current = packet;
							let found = false;
							const lookahead = 6; // Heuristic, but should be enough for most streams

							for (let i = 0; i < lookahead; i++) {
								const next = await sink.getNextPacket(current, { metadataOnly: true });
								if (!next) {
									break;
								}

								if (next.timestamp < this._endTimestamp) {
									found = true;
									break;
								}

								current = next;
							}

							if (!found) {
								break;
							}
						}
					}

					let packetStartTimestamp = packet.timestamp;
					let packetEndTimestamp = packet.timestamp + packet.duration;

					if (this._copyBoundaryPolicy === 'shrink') {
						packetStartTimestamp = Math.max(packetStartTimestamp, this._startTimestamp);
						packetEndTimestamp = Math.min(packetEndTimestamp, this._endTimestamp);
						packetEndTimestamp = Math.max(packetEndTimestamp, packetStartTimestamp); // Just in case
					}

					packetStartTimestamp += this._timestampOffset;
					packetEndTimestamp += this._timestampOffset;

					const modifiedPacket = packet.clone({
						timestamp: packetStartTimestamp,
						duration: packetEndTimestamp - packetStartTimestamp,
						sideData: alpha === 'discard'
							? {} // Remove alpha side data
							: packet.sideData,
					});

					this._reportProgress(outputTrackId, modifiedPacket.timestamp + modifiedPacket.duration);
					await source.add(modifiedPacket, meta);

					if (this._synchronizer.shouldWait(outputTrackId, modifiedPacket.timestamp)) {
						await this._synchronizer.wait(modifiedPacket.timestamp);
					}

					await this._checkpoint(pump, modifiedPacket.timestamp);
				}

				source.close();
				this._synchronizer.closeTrack(outputTrackId);
			});
		} else {
			// We need to decode & reencode the video

			const canDecode = await track.canDecode();
			if (!canDecode) {
				this.discardedTracks.push({
					track,
					reason: 'undecodable_source_codec',
					trackOptions,
				});
				return;
			}

			if (trackOptions.codec) {
				videoCodecs = videoCodecs.filter(codec => codec === trackOptions.codec);
			}

			// eslint-disable-next-line @typescript-eslint/no-deprecated
			const quality = resolveQuality(trackOptions.quality, trackOptions.bitrate)
				?? new Quality('high');

			const encodableCodec = await getFirstEncodableVideoCodec(videoCodecs, {
				width: trackOptions.process && trackOptions.processedWidth
					? trackOptions.processedWidth
					: width,
				height: trackOptions.process && trackOptions.processedHeight
					? trackOptions.processedHeight
					: height,
				quality,
			});
			if (!encodableCodec) {
				this.discardedTracks.push({
					track,
					reason: 'no_encodable_target_codec',
					trackOptions,
				});
				return;
			}

			const encodingConfig: VideoEncodingConfig = {
				codec: encodableCodec,
				quality,
				keyFrameInterval: trackOptions.keyFrameInterval,
				sizeChangeBehavior: trackOptions.fit ?? 'passThrough',
				alpha,
				hardwareAcceleration: trackOptions.hardwareAcceleration,
				transform: {},
			};
			assert(encodingConfig.transform);

			let needsRerender = width !== originalWidth
				|| height !== originalHeight
				|| (totalRotation !== 0 && (!canUseRotationMetadata || trackOptions.process !== undefined))
				|| !!crop
				// Don't expect encoders to reliably handle non-square pixels:
				|| squarePixelWidth !== await track.getCodedWidth()
				|| squarePixelHeight !== await track.getCodedHeight();

			if (!needsRerender) {
				// If we're directly passing decoded samples back to the encoder, sometimes the encoder may error due
				// to lack of support of certain video frame formats, like when HDR is at play. To check for this, we
				// first try to pass a single frame to the encoder to see how it behaves. If it throws, we then fall
				// back to the rerender path.
				//
				// Creating a new temporary Output is sort of hacky, but due to a lack of an isolated encoder API right
				// now, this is the simplest way. Will refactor in the future! TODO

				const tempOutput = new Output({
					format: new Mp4OutputFormat(), // Supports all video codecs
					target: new NullTarget(),
				});

				const tempSource = new VideoSampleSource(encodingConfig);
				tempOutput.addVideoTrack(tempSource);

				await tempOutput.start();

				// Let's just use the first sample to test
				const sink = new VideoSampleSink(track);
				using firstSample = await sink.getSample(await track.getFirstTimestamp());

				if (firstSample) {
					try {
						await tempSource.add(firstSample);
						firstSample.close();
						await tempOutput.finalize();
					} catch (error) {
						Logging._warn(
							'An error occurred when probing encoder support. Falling back to rerender path.', error,
						);
						void tempOutput.cancel();

						needsRerender = true;
						encodingConfig.transform.force = true;
					}
				} else {
					await tempOutput.cancel();
				}
			}

			if (trackOptions.frameRate) {
				encodingConfig.transform.frameRate = trackOptions.frameRate;
			}

			if (trackOptions.process) {
				encodingConfig.transform.process = trackOptions.process;
			}

			if (needsRerender) {
				outputTrackRotation = 0; // Since the rotation is baked into the output

				encodingConfig.transform.width = width;
				encodingConfig.transform.height = height;
				encodingConfig.transform.fit = trackOptions.fit ?? 'fill';
				encodingConfig.transform.rotate = normalizeRotation(totalRotation - innateRotation);
				encodingConfig.transform.crop = crop;
				encodingConfig.transform.alpha = alpha;
			}

			// We need to do this because `process` can emit new timestamps
			let lastSampleTimestamp: number | null = null;
			encodingConfig.onEncodedSample = (sample) => {
				lastSampleTimestamp = sample.timestamp;
			};

			const source = new VideoSampleSource(encodingConfig);
			videoSource = source;

			this._registerTrackPump(async (pump) => {
				const sink = new VideoSampleSink(track);

				for await (using sample of sink.samples(this._startTimestamp, this._endTimestamp)) {
					if (this._state === 'canceled') {
						break;
					}

					const adjustedSampleTimestamp = Math.max(0, sample.timestamp + this._timestampOffset);
					sample.setTimestamp(adjustedSampleTimestamp);

					this._reportProgress(outputTrackId, sample.timestamp + sample.duration);
					await source.add(sample);
					sample.close();

					if (lastSampleTimestamp !== null) {
						if (this._synchronizer.shouldWait(outputTrackId, lastSampleTimestamp)) {
							await this._synchronizer.wait(lastSampleTimestamp);
						}

						await this._checkpoint(pump, lastSampleTimestamp);
					}
				}

				source.close();
				this._synchronizer.closeTrack(outputTrackId);
			});
		}

		let ownGroup: OutputTrackGroup | null = null;
		if (!trackOptions.group && !this._composable) {
			// Create per-track groups to replicate the input's pairability graph. Don't do this for composable
			// conversions.
			ownGroup = new OutputTrackGroup();
		}

		const videoTrackLanguageCode = await track.getLanguageCode();
		const trackName = await track.getName();
		const trackDisposition = await track.getDisposition();

		this.output.addVideoTrack(videoSource, {
			frameRate: trackOptions.frameRate,
			// TODO: This condition can be removed when all demuxers properly homogenize to BCP47 in v2
			languageCode: isIso639Dash2LanguageCode(videoTrackLanguageCode)
				? videoTrackLanguageCode
				: undefined,
			name: trackName ?? undefined,
			disposition: trackDisposition,
			rotation: outputTrackRotation,
			group: ownGroup ?? trackOptions.group,
		});

		this.utilizedTracks.push(track);
		this._outputTrackIds.push(outputTrackId);
		this._outputOwnTrackGroups.push(ownGroup);
	}

	/** @internal */
	async _processAudioTrack(track: InputAudioTrack, trackOptions: ConversionAudioOptions, outputTrackId: number) {
		const sourceCodec = await track.getCodec();
		if (!sourceCodec) {
			this.discardedTracks.push({
				track,
				reason: 'unknown_source_codec',
				trackOptions,
			});
			return;
		}

		let audioSource: AudioSource;

		const originalNumberOfChannels = await track.getNumberOfChannels();
		const originalSampleRate = await track.getSampleRate();

		let numberOfChannels = trackOptions.numberOfChannels ?? originalNumberOfChannels;
		let sampleRate = trackOptions.sampleRate ?? originalSampleRate;

		let audioCodecs = this.output.format.getSupportedAudioCodecs();

		let needsTranscode = !this._copyMode
			|| !!trackOptions.forceTranscode
			|| !!trackOptions.quality
			// eslint-disable-next-line @typescript-eslint/no-deprecated
			|| !!trackOptions.bitrate
			|| numberOfChannels !== originalNumberOfChannels
			|| sampleRate !== originalSampleRate
			|| !audioCodecs.includes(sourceCodec)
			|| (!!trackOptions.codec && trackOptions.codec !== sourceCodec)
			|| trackOptions.process !== undefined
			|| trackOptions.sampleFormat !== undefined;

		let copyStartPacket: EncodedPacket | null = null;

		if (!needsTranscode) {
			// Check if we can copy it
			const sink = new EncodedPacketSink(track);
			let startPacket = await sink.getKeyPacket(this._startTimestamp)
				?? await sink.getFirstKeyPacket();

			if (
				startPacket
				&& startPacket.timestamp < this._startTimestamp
				&& this._copyBoundaryPolicy === 'shrink'
			) {
				startPacket = await sink.getNextKeyPacket(startPacket);
			}

			const hasDecoderWarmup = (NON_PCM_AUDIO_CODECS as readonly AudioCodec[]).includes(sourceCodec)
				&& sourceCodec !== 'flac';
			if (startPacket && this._copyBoundaryPolicy === 'expand' && hasDecoderWarmup) {
				// Go one packet back
				const previousPacket = await sink.getKeyPacket(
					startPacket.timestamp - 1 / (await track.getTimeResolution()),
				);
				if (previousPacket) {
					startPacket = previousPacket;
				}
			}

			copyStartPacket = startPacket;

			if (startPacket) {
				if (!this.output.format.supportsTimestampedMediaData) {
					// Wants zero

					if (this._timestampOffsetAdjusted) {
						// We've already adjusted, we can't adjust twice
						const isValid = startPacket.timestamp + this._timestampOffset === 0;
						if (!isValid) {
							needsTranscode = true;
						}
					} else {
						const correction = clamp(
							this._startTimestamp - startPacket.timestamp,
							-this._copyTimestampShiftTolerance,
							this._copyTimestampShiftTolerance,
						);

						const shiftedStartTimestamp = startPacket.timestamp + correction;
						const isValid = shiftedStartTimestamp === this._startTimestamp;

						if (isValid) {
							this._timestampOffset = -this._startTimestamp + correction;
							this._timestampOffsetAdjusted = true;
						} else {
							needsTranscode = true;
						}
					}
				} else if (
					this.output.format.negativeTimestampSupport !== 'full'
					&& startPacket.timestamp < this._startTimestamp
				) {
					const correction = Math.min(
						this._startTimestamp - startPacket.timestamp,
						this._copyTimestampShiftTolerance,
					);

					const shiftedStartTimestamp = startPacket.timestamp + correction;
					const isValid = shiftedStartTimestamp >= this._startTimestamp
						|| (
							this.output.format.negativeTimestampSupport === 'prefer-non-negative'
							&& this._copyMode === 'forced'
						);

					if (isValid) {
						this._timestampOffset = Math.max(this._timestampOffset, -this._startTimestamp + correction);
					} else {
						needsTranscode = true;
					}
				}
			}
		}

		if (needsTranscode && this._copyMode === 'forced') {
			this.discardedTracks.push({
				track,
				reason: 'cannot_copy',
				trackOptions,
			});
			return;
		}

		if (!needsTranscode) {
			// Fast path, we can simply copy over the encoded packets

			const source = new EncodedAudioPacketSource(sourceCodec);
			audioSource = source;

			this._registerTrackPump(async (pump) => {
				const sink = new EncodedPacketSink(track);
				const decoderConfig = await track.getDecoderConfig();
				const meta: EncodedAudioChunkMetadata = { decoderConfig: decoderConfig ?? undefined };

				// eslint-disable-next-line curly
				if (copyStartPacket) for await (const packet of sink.packets(copyStartPacket)) {
					if (this._state === 'canceled') {
						break;
					}

					if (packet.timestamp >= this._endTimestamp) {
						break;
					}
					if (
						this._copyBoundaryPolicy === 'shrink'
						&& packet.timestamp + packet.duration > this._endTimestamp
					) {
						break;
					}

					const modifiedPacket = packet.clone({
						timestamp: packet.timestamp + this._timestampOffset,
						duration: packet.duration,
					});

					this._reportProgress(outputTrackId, modifiedPacket.timestamp + modifiedPacket.duration);
					await source.add(modifiedPacket, meta);

					if (this._synchronizer.shouldWait(outputTrackId, modifiedPacket.timestamp)) {
						await this._synchronizer.wait(modifiedPacket.timestamp);
					}

					await this._checkpoint(pump, modifiedPacket.timestamp);
				}

				source.close();
				this._synchronizer.closeTrack(outputTrackId);
			});
		} else {
			// We need to decode & reencode the audio

			const canDecode = await track.canDecode();
			if (!canDecode) {
				this.discardedTracks.push({
					track,
					reason: 'undecodable_source_codec',
					trackOptions,
				});
				return;
			}

			let codecOfChoice: AudioCodec | null = null;

			if (trackOptions.codec) {
				audioCodecs = audioCodecs.filter(codec => codec === trackOptions.codec);
			}

			// eslint-disable-next-line @typescript-eslint/no-deprecated
			const quality = resolveQuality(trackOptions.quality, trackOptions.bitrate)
				?? new Quality('high');

			const encodableCodecs = await getEncodableAudioCodecs(audioCodecs, {
				numberOfChannels: trackOptions.process && trackOptions.processedNumberOfChannels
					? trackOptions.processedNumberOfChannels
					: numberOfChannels,
				sampleRate: trackOptions.process && trackOptions.processedSampleRate
					? trackOptions.processedSampleRate
					: sampleRate,
				quality,
			});

			if (
				!encodableCodecs.some(codec => (NON_PCM_AUDIO_CODECS as readonly string[]).includes(codec))
				&& audioCodecs.some(codec => (NON_PCM_AUDIO_CODECS as readonly string[]).includes(codec))
				&& (numberOfChannels !== FALLBACK_NUMBER_OF_CHANNELS || sampleRate !== FALLBACK_SAMPLE_RATE)
			) {
				// We could not find a compatible non-PCM codec despite the container supporting them. This can be
				// caused by strange channel count or sample rate configurations. Therefore, let's try again but with
				// fallback parameters.

				const encodableCodecsWithDefaultParams = await getEncodableAudioCodecs(audioCodecs, {
					numberOfChannels: FALLBACK_NUMBER_OF_CHANNELS,
					sampleRate: FALLBACK_SAMPLE_RATE,
					quality,
				});

				const nonPcmCodec = encodableCodecsWithDefaultParams
					.find(codec => (NON_PCM_AUDIO_CODECS as readonly string[]).includes(codec));
				if (nonPcmCodec) {
					// We are able to encode using a non-PCM codec, but it'll require resampling
					codecOfChoice = nonPcmCodec;
					numberOfChannels = FALLBACK_NUMBER_OF_CHANNELS;
					sampleRate = FALLBACK_SAMPLE_RATE;
				}
			} else {
				codecOfChoice = encodableCodecs[0] ?? null;
			}

			if (codecOfChoice === null) {
				this.discardedTracks.push({
					track,
					reason: 'no_encodable_target_codec',
					trackOptions,
				});
				return;
			}

			const encodingConfig: AudioEncodingConfig = {
				codec: codecOfChoice,
				quality,
				transform: {
					sampleFormat: trackOptions.sampleFormat,
					process: trackOptions.process,
				},
			};
			assert(encodingConfig.transform);

			if (numberOfChannels !== originalNumberOfChannels) {
				encodingConfig.transform.numberOfChannels = numberOfChannels;
			}
			if (sampleRate !== originalSampleRate) {
				encodingConfig.transform.sampleRate = sampleRate;
			}

			let lastSampleTimestamp: number | null = null;
			encodingConfig.onEncodedSample = (sample) => {
				lastSampleTimestamp = sample.timestamp;
			};

			const source = new AudioSampleSource(encodingConfig);
			audioSource = source;

			this._registerTrackPump(async (pump) => {
				let needsPadding: boolean | null = null;

				const sink = new AudioSampleSink(track);
				for await (using sample of sink.samples(this._startTimestamp, this._endTimestamp)) {
					if (this._state === 'canceled') {
						break;
					}

					let startFrame = 0;
					let endFrame = sample.numberOfFrames;

					if (sample.timestamp < this._startTimestamp) {
						startFrame = Math.round((this._startTimestamp - sample.timestamp) * sample.sampleRate);
					}
					if (sample.timestamp + sample.duration > this._endTimestamp) {
						endFrame = Math.round((this._endTimestamp - sample.timestamp) * sample.sampleRate);
					}

					// Can't assign to "using" identifiers so we gotta do this
					let finalSampleLet: AudioSample;
					if (startFrame > 0 || endFrame < sample.numberOfFrames) {
						// Trim the sample if it sticks out of the trim region on either end
						const trimmedSample = sample.trim(startFrame, endFrame);
						sample.close();
						finalSampleLet = trimmedSample;

						if (trimmedSample.numberOfFrames === 0) {
							trimmedSample.close();
							continue;
						}
					} else {
						finalSampleLet = sample;
					}

					using finalSample = finalSampleLet;

					// Offset the timestamp as needed
					finalSample.setTimestamp(finalSample.timestamp + this._timestampOffset);

					if (needsPadding === null) {
						needsPadding = finalSample.timestamp > 0 && !this.output.format.supportsTimestampedMediaData;
					}

					if (needsPadding) {
						// Add one padding sample at the beginning
						const paddingLength = finalSample.timestamp;
						const paddingLengthSamples = Math.round(paddingLength * originalSampleRate);

						const bytesPerSample = getBytesPerSample(sample.format);
						const data = new Uint8Array(bytesPerSample * paddingLengthSamples * originalNumberOfChannels);
						if (sample.format === 'u8' || sample.format === 'u8-planar') {
							data.fill(2 ** 7); // Fill it with the silent value
						}

						using silentSample = new AudioSample({
							data,
							// Use the same format the decoder is spitting out. This avoids feeding changing sample
							// formats to the audio encoder.
							format: sample.format,
							numberOfChannels: originalNumberOfChannels,
							sampleRate: originalSampleRate,
							timestamp: 0,
						});
						await this._registerAudioSample(
							pump, silentSample, source, outputTrackId, () => lastSampleTimestamp,
						);

						needsPadding = false;
					}

					await this._registerAudioSample(
						pump, finalSample, source, outputTrackId, () => lastSampleTimestamp,
					);
				}

				source.close();
				this._synchronizer.closeTrack(outputTrackId);
			});
		}

		let ownGroup: OutputTrackGroup | null = null;
		if (!trackOptions.group && !this._composable) {
			// Create per-track groups to replicate the input's pairability graph. Don't do this for composable
			// conversions.
			ownGroup = new OutputTrackGroup();
		}

		const audioTrackLanguageCode = await track.getLanguageCode();
		const trackName = await track.getName();
		const trackDisposition = await track.getDisposition();

		this.output.addAudioTrack(audioSource, {
			// TODO: This condition can be removed when all demuxers properly homogenize to BCP47 in v2
			languageCode: isIso639Dash2LanguageCode(audioTrackLanguageCode)
				? audioTrackLanguageCode
				: undefined,
			name: trackName ?? undefined,
			disposition: trackDisposition,
			group: ownGroup ?? trackOptions.group,
		});

		this.utilizedTracks.push(track);
		this._outputTrackIds.push(outputTrackId);
		this._outputOwnTrackGroups.push(ownGroup);
	}

	/** @internal */
	async _registerAudioSample(
		pump: TrackPump,
		sample: AudioSample,
		source: AudioSampleSource,
		outputTrackId: number,
		getLastSampleTimestamp: () => number | null,
	) {
		this._reportProgress(outputTrackId, sample.timestamp + sample.duration);

		await source.add(sample);
		sample.close();

		const lastSampleTimestamp = getLastSampleTimestamp();
		if (lastSampleTimestamp !== null) {
			if (this._synchronizer.shouldWait(outputTrackId, lastSampleTimestamp)) {
				await this._synchronizer.wait(lastSampleTimestamp);
			}

			await this._checkpoint(pump, lastSampleTimestamp);
		}
	}

	/** @internal */
	_registerTrackPump(fn: (pump: TrackPump) => Promise<void>) {
		const pump: TrackPump = {
			done: false,
			resolvers: promiseWithResolvers(),
			wake: null,
			start: () => {
				void fn(pump).then(() => {
					pump.done = true;
					pump.resolvers.resolve();
				}, (error) => {
					pump.resolvers.reject(error);
				});
			},
		};

		this._trackPumps.push(pump);
	}

	/** @internal */
	async _checkpoint(pump: TrackPump, timestamp: number) {
		while (this._state !== 'canceled' && (timestamp >= this._executionUntil || this._pauseRequested)) {
			// We've reached the target; signal it and suspend until the next execution wakes us up
			pump.resolvers.resolve();

			const { promise, resolve } = promiseWithResolvers();
			pump.wake = resolve;
			await promise;
		}
	}

	/** @internal */
	_reportProgress(trackId: number, endTimestamp: number) {
		if (!this._computeProgress) {
			return;
		}
		assert(this._totalDuration !== null);

		this._maxTimestamps.set(
			trackId,
			Math.max(endTimestamp, this._maxTimestamps.get(trackId)!),
		);

		const minTimestamp = Math.min(...this._maxTimestamps.values());
		const newProgress = clamp(minTimestamp / this._totalDuration, 0, 1);

		if (newProgress !== this._lastProgress) {
			this._lastProgress = newProgress;
			this.onProgress?.(newProgress, minTimestamp);
		}
	}
}

/**
 * Thrown when a conversion couldn't complete due to being canceled.
 * @group Conversion
 * @public
 */
export class ConversionCanceledError extends Error {
	/** Creates a new {@link ConversionCanceledError}. */
	constructor(message = 'Conversion has been canceled.') {
		super(message);
		this.name = 'ConversionCanceledError';
	}
}

const MAX_TIMESTAMP_GAP = 1; // in seconds

/**
 * Utility class for synchronizing multiple track packet consumers with one another. We don't want one consumer to get
 * too out-of-sync with the others, as that may lead to a large number of packets that need to be internally buffered
 * before they can be written. Therefore, we use this class to slow down a consumer if it is too far ahead of the
 * slowest consumer.
 */
class TrackSynchronizer {
	conversion: Conversion;
	maxTimestamps = new Map<number, number>(); // Track ID -> timestamp
	resolvers: {
		timestamp: number;
		resolve: () => void;
	}[] = [];

	constructor(conversion: Conversion) {
		this.conversion = conversion;
	}

	declareTrack(trackId: number) {
		// Using -Infinity will automatically cause all tracks to wait for each other at the start until they figure out
		// the true min timestamp
		this.maxTimestamps.set(trackId, -Infinity);
	}

	shouldWait(trackId: number, timestamp: number) {
		const currentValue = this.maxTimestamps.get(trackId);
		assert(currentValue !== undefined);

		this.maxTimestamps.set(trackId, Math.max(timestamp, currentValue));

		const newMin = this.computeMinAndMaybeResolve();
		if (
			this.conversion._state === 'canceled'
			|| this.conversion._pauseRequested
			|| timestamp >= this.conversion._executionUntil
		) {
			// No point in throttling consumers that are about to suspend or wind down anyway
			return false;
		}

		return timestamp - newMin > MAX_TIMESTAMP_GAP; // Should wait if it is too far ahead of the slowest consumer
	}

	wait(timestamp: number) {
		const { promise, resolve } = promiseWithResolvers();

		this.resolvers.push({
			timestamp,
			resolve,
		});

		return promise;
	}

	closeTrack(trackId: number) {
		this.maxTimestamps.delete(trackId);
		this.computeMinAndMaybeResolve();
	}

	resolveAll() {
		for (const entry of this.resolvers) {
			entry.resolve();
		}
		this.resolvers.length = 0;
	}

	computeMinAndMaybeResolve() {
		let newMin = Infinity;
		for (const [, timestamp] of this.maxTimestamps) {
			newMin = Math.min(newMin, timestamp);
		}

		for (let i = 0; i < this.resolvers.length; i++) {
			const entry = this.resolvers[i]!;

			if (entry.timestamp - newMin < MAX_TIMESTAMP_GAP) {
				// The gap has gotten small enough again, the consumer can continue again
				entry.resolve();
				this.resolvers.splice(i, 1);
				i--;
			}
		}

		return newMin;
	}
}