audio-buffer/index.js

AudioBuffer ponyfill with operations toolkit

/**
 * AudioBuffer — spec-compliant audio data container
 *
 * Supports both spec constructor forms:
 *   new AudioBuffer({ length, sampleRate, numberOfChannels })
 *   new AudioBuffer(numberOfChannels, length, sampleRate)
 */

const _Error = globalThis.DOMException || Error

export default class AudioBuffer {
	#sampleRate
	#length
	#duration
	#numberOfChannels
	#data    // Float32Array — planar storage of all channels
	#channels // Float32Array[] — subarray views per channel

	get sampleRate() { return this.#sampleRate }
	get length() { return this.#length }
	get duration() { return this.#duration }
	get numberOfChannels() { return this.#numberOfChannels }

	// internal: array of per-channel Float32Array views
	get _channels() { return this.#channels }

	constructor(options, length, sampleRate) {
		// positional form: new AudioBuffer(numberOfChannels, length, sampleRate)
		if (typeof options === 'number')
			options = { numberOfChannels: options, length, sampleRate }

		if (!options || typeof options !== 'object') throw new TypeError('options must be a dictionary')

		// required options — TypeError if missing
		if (options.sampleRate == null) throw new TypeError('options.sampleRate is required')
		if (options.length == null) throw new TypeError('options.length is required')

		// value validation — DOMException NotSupportedError
		if (!(options.sampleRate >= 3000 && options.sampleRate <= 768000))
			throw new _Error('sampleRate ' + options.sampleRate + ' outside valid range [3000, 768000]', 'NotSupportedError')
		if (!(options.length >= 1))
			throw new _Error('length must be > 0', 'NotSupportedError')
		if (options.numberOfChannels != null && !(options.numberOfChannels >= 1))
			throw new _Error('numberOfChannels must be > 0', 'NotSupportedError')

		let nch = options.numberOfChannels || 1
		let len = Math.trunc(options.length)

		this.#sampleRate = options.sampleRate
		this.#numberOfChannels = nch
		this.#length = len
		this.#duration = len / options.sampleRate

		this.#data = new Float32Array(len * nch)
		let channels = this.#channels = new Array(nch)
		for (let c = 0; c < nch; c++)
			channels[c] = this.#data.subarray(c * len, (c + 1) * len)
	}

	getChannelData(channel) {
		if (channel == null || channel < 0 || channel >= this.#numberOfChannels)
			throw new _Error('channel index (' + channel + ') exceeds numberOfChannels (' + this.#numberOfChannels + ')', 'IndexSizeError')
		return this.#channels[channel]
	}

	copyFromChannel(destination, channelNumber, startInChannel = 0) {
		if (!(destination instanceof Float32Array)) throw new TypeError('destination must be a Float32Array')
		if (typeof SharedArrayBuffer !== 'undefined' && destination.buffer instanceof SharedArrayBuffer)
			throw new TypeError('destination must not be backed by a SharedArrayBuffer')
		if (channelNumber < 0 || channelNumber >= this.#numberOfChannels)
			throw new _Error('channel index out of bounds', 'IndexSizeError')
		// WebIDL unsigned long: clamp negative / overflow to uint32
		startInChannel = startInChannel < 0 ? (startInChannel >>> 0) : startInChannel
		let data = this.#channels[channelNumber]
		let len = Math.min(destination.length, this.#length - startInChannel)
		if (len > 0) destination.set(data.subarray(startInChannel, startInChannel + len))
	}

	copyToChannel(source, channelNumber, startInChannel = 0) {
		if (!(source instanceof Float32Array)) throw new TypeError('source must be a Float32Array')
		if (typeof SharedArrayBuffer !== 'undefined' && source.buffer instanceof SharedArrayBuffer)
			throw new TypeError('source must not be backed by a SharedArrayBuffer')
		if (channelNumber < 0 || channelNumber >= this.#numberOfChannels)
			throw new _Error('channel index out of bounds', 'IndexSizeError')
		// WebIDL unsigned long: clamp negative / overflow to uint32
		startInChannel = startInChannel < 0 ? (startInChannel >>> 0) : startInChannel
		let data = this.#channels[channelNumber]
		let len = Math.min(source.length, this.#length - startInChannel)
		if (len > 0) data.set(source.subarray(0, len), startInChannel)
	}

	*[Symbol.iterator]() {
		for (let c = 0; c < this.#numberOfChannels; c++) yield this.#channels[c]
	}
}