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https://github.com/th-ch/youtube-music.git
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Add first version for crossfade plugin
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TC
360
plugins/crossfade/fader.js
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360
plugins/crossfade/fader.js
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/**
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* VolumeFader
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* Sophisticated Media Volume Fading
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*
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* Requires browser support for:
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* - HTMLMediaElement
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* - requestAnimationFrame()
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* - ES6
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*
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* Does not depend on any third-party library.
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*
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* License: MIT
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*
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* Nick Schwarzenberg
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* v0.2.0, 07/2016
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*/
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(function (root) {
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"use strict";
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// internal utility: check if value is a valid volume level and throw if not
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let validateVolumeLevel = (value) => {
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// number between 0 and 1?
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if (!Number.isNaN(value) && value >= 0 && value <= 1) {
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// yup, that's fine
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return;
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} else {
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// abort and throw an exception
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throw new TypeError("Number between 0 and 1 expected as volume!");
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}
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};
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// main class
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class VolumeFader {
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/**
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* VolumeFader Constructor
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*
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* @param media {HTMLMediaElement} - audio or video element to be controlled
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* @param options {Object} - an object with optional settings
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* @throws {TypeError} if options.initialVolume or options.fadeDuration are invalid
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*
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* options:
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* .logger: {Function} logging `function(stuff, …)` for execution information (default: no logging)
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* .fadeScaling: {Mixed} either 'linear', 'logarithmic' or a positive number in dB (default: logarithmic)
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* .initialVolume: {Number} media volume 0…1 to apply during setup (volume not touched by default)
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* .fadeDuration: {Number} time in milliseconds to complete a fade (default: 1000 ms)
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*/
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constructor(media, options) {
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// passed media element of correct type?
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if (media instanceof HTMLMediaElement) {
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// save reference to media element
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this.media = media;
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} else {
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// abort and throw an exception
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throw new TypeError("Media element expected!");
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}
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// make sure options is an object
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options = options || {};
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// log function passed?
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if (typeof options.logger == "function") {
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// set log function to the one specified
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this.logger = options.logger;
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} else {
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// set log function explicitly to false
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this.logger = false;
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}
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// linear volume fading?
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if (options.fadeScaling == "linear") {
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// pass levels unchanged
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this.scale = {
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internalToVolume: (level) => level,
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volumeToInternal: (level) => level,
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};
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// log setting
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this.logger && this.logger("Using linear fading.");
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}
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// no linear, but logarithmic fading…
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else {
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let dynamicRange;
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// default dynamic range?
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if (
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options.fadeScaling === undefined ||
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options.fadeScaling == "logarithmic"
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) {
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// set default of 60 dB
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dynamicRange = 3;
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}
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// custom dynamic range?
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else if (
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!Number.isNaN(options.fadeScaling) &&
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options.fadeScaling > 0
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) {
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// turn amplitude dB into a multiple of 10 power dB
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dynamicRange = options.fadeScaling / 2 / 10;
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}
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// unsupported value
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else {
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// abort and throw exception
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throw new TypeError(
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"Expected 'linear', 'logarithmic' or a positive number as fade scaling preference!"
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);
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}
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// use exponential/logarithmic scaler for expansion/compression
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this.scale = {
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internalToVolume: (level) =>
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this.exponentialScaler(level, dynamicRange),
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volumeToInternal: (level) =>
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this.logarithmicScaler(level, dynamicRange),
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};
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// log setting if not default
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options.fadeScaling &&
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this.logger &&
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this.logger(
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"Using logarithmic fading with " +
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String(10 * dynamicRange) +
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" dB dynamic range."
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);
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}
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// set initial volume?
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if (options.initialVolume !== undefined) {
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// validate volume level and throw if invalid
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validateVolumeLevel(options.initialVolume);
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// set initial volume
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this.media.volume = options.initialVolume;
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// log setting
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this.logger &&
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this.logger(
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"Set initial volume to " + String(this.media.volume) + "."
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);
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}
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// fade duration given?
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if (options.fadeDuration !== undefined) {
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// try to set given fade duration (will log if successful and throw if not)
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this.setFadeDuration(options.fadeDuration);
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} else {
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// set default fade duration (1000 ms)
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this.fadeDuration = 1000;
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}
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// indicate that fader is not active yet
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this.active = false;
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// initialization done
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this.logger && this.logger("Initialized for", this.media);
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}
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/**
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* Re(start) the update cycle.
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* (this.active must be truthy for volume updates to take effect)
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*
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* @return {Object} VolumeFader instance for chaining
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*/
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start() {
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// set fader to be active
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this.active = true;
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// start by running the update method
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this.updateVolume();
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// return instance for chaining
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return this;
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}
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/**
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* Stop the update cycle.
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* (interrupting any fade)
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*
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* @return {Object} VolumeFader instance for chaining
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*/
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stop() {
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// set fader to be inactive
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this.active = false;
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// return instance for chaining
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return this;
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}
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/**
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* Set fade duration.
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* (used for future calls to fadeTo)
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*
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* @param {Number} fadeDuration - fading length in milliseconds
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* @throws {TypeError} if fadeDuration is not a number greater than zero
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* @return {Object} VolumeFader instance for chaining
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*/
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setFadeDuration(fadeDuration) {
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// if duration is a valid number > 0…
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if (!Number.isNaN(fadeDuration) && fadeDuration > 0) {
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// set fade duration
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this.fadeDuration = fadeDuration;
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// log setting
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this.logger &&
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this.logger("Set fade duration to " + String(fadeDuration) + " ms.");
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} else {
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// abort and throw an exception
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throw new TypeError("Positive number expected as fade duration!");
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}
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// return instance for chaining
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return this;
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}
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/**
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* Define a new fade and start fading.
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*
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* @param {Number} targetVolume - level to fade to in the range 0…1
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* @param {Function} callback - (optional) function to be called when fade is complete
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* @throws {TypeError} if targetVolume is not in the range 0…1
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* @return {Object} VolumeFader instance for chaining
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*/
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fadeTo(targetVolume, callback) {
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// validate volume and throw if invalid
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validateVolumeLevel(targetVolume);
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// define new fade
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this.fade = {
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// volume start and end point on internal fading scale
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volume: {
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start: this.scale.volumeToInternal(this.media.volume),
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end: this.scale.volumeToInternal(targetVolume),
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},
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// time start and end point
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time: {
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start: Date.now(),
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end: Date.now() + this.fadeDuration,
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},
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// optional callback function
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callback: callback,
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};
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// start fading
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this.start();
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// log new fade
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this.logger && this.logger("New fade started:", this.fade);
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// return instance for chaining
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return this;
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}
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// convenience shorthand methods for common fades
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fadeIn(callback) {
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this.fadeTo(1, callback);
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}
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fadeOut(callback) {
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this.fadeTo(0, callback);
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}
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/**
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* Internal: Update media volume.
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* (calls itself through requestAnimationFrame)
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*
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* @param {Number} targetVolume - linear level to fade to (0…1)
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* @param {Function} callback - (optional) function to be called when fade is complete
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*/
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updateVolume() {
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// fader active and fade available to process?
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if (this.active && this.fade) {
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// get current time
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let now = Date.now();
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// time left for fading?
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if (now < this.fade.time.end) {
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// compute current fade progress
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let progress =
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(now - this.fade.time.start) /
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(this.fade.time.end - this.fade.time.start);
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// compute current level on internal scale
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let level =
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progress * (this.fade.volume.end - this.fade.volume.start) +
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this.fade.volume.start;
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// map fade level to volume level and apply it to media element
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this.media.volume = this.scale.internalToVolume(level);
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// schedule next update
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root.requestAnimationFrame(this.updateVolume.bind(this));
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} else {
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// log end of fade
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this.logger &&
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this.logger(
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"Fade to " + String(this.fade.volume.end) + " complete."
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);
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// time is up, jump to target volume
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this.media.volume = this.scale.internalToVolume(this.fade.volume.end);
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// set fader to be inactive
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this.active = false;
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// done, call back (if callable)
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typeof this.fade.callback == "function" && this.fade.callback();
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// clear fade
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this.fade = undefined;
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}
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}
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}
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/**
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* Internal: Exponential scaler with dynamic range limit.
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*
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* @param {Number} input - logarithmic input level to be expanded (float, 0…1)
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* @param {Number} dynamicRange - expanded output range, in multiples of 10 dB (float, 0…∞)
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* @return {Number} - expanded level (float, 0…1)
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*/
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exponentialScaler(input, dynamicRange) {
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// special case: make zero (or any falsy input) return zero
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if (input == 0) {
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// since the dynamic range is limited,
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// allow a zero to produce a plain zero instead of a small faction
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// (audio would not be recognized as silent otherwise)
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return 0;
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} else {
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// scale 0…1 to minus something × 10 dB
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input = (input - 1) * dynamicRange;
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// compute power of 10
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return Math.pow(10, input);
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}
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}
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/**
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* Internal: Logarithmic scaler with dynamic range limit.
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*
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* @param {Number} input - exponential input level to be compressed (float, 0…1)
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* @param {Number} dynamicRange - coerced input range, in multiples of 10 dB (float, 0…∞)
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* @return {Number} - compressed level (float, 0…1)
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*/
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logarithmicScaler(input, dynamicRange) {
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// special case: make zero (or any falsy input) return zero
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if (input == 0) {
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// logarithm of zero would be -∞, which would map to zero anyway
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return 0;
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} else {
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// compute base-10 logarithm
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input = Math.log10(input);
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// scale minus something × 10 dB to 0…1 (clipping at 0)
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return Math.max(1 + input / dynamicRange, 0);
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}
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}
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}
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// export class to root scope
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root.VolumeFader = VolumeFader;
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})(window);
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