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1.5.5 • Public • Published

Gapless 5  

A gapless JavaScript audio player using HTML5 and WebAudio.

PROBLEM: There are 2 modern APIs for playing audio through the web, and both of them have problems:

  • HTML5 Audio: the last chunk of audio gets cut off, making gapless transitions impossible
  • WebAudio: can't play a file until it's fully loaded

SOLUTION: Use both!

  • If WebAudio hasn't fully loaded yet, it begins playback with HTML5 Audio, then seamlessly switches to WebAudio once loaded.

1. Demos

The following sites utilize Gapless 5. If you'd like to be featured here, please contact the repo owner or start a new issue!

2. Features

  • Players can have multiple tracks
  • Pages can have multiple players
  • Memory management (see loadLimit under Options)
  • Seamless transitions between tracks
    • Pre-loading of subsequent tracks
    • Files don't need to be fully loaded to start playback
  • Cross-fade support
  • Track shuffling during playback
  • Optional built-in UI

2.1. Browser Support

  • Safari (including iOS)
  • Chrome (including Android)
  • Firefox
  • Other browers (UI untested, but they probably work as well)

NOTE for Boostrap users: Bootstrap's CSS will mess up the optional built-in UI. If you don't need Bootstrap in its entirety, try using Twitter customize to get just the subset of rules you need.

3. Installation

3.1. Using npm

  1. Install the npm package:
$ npm install @regosen/gapless-5
  1. Import Gapless5 from the module:
const { Gapless5 } = require('@regosen/gapless-5');

3.2. Using direct HTML

A. If not using built-in UI, just add and reference Gapless5.js from your HTML head.

<script src="gapless5.js" language="JavaScript" type="text/javascript"></script>

B. If using the built-in UI, add and reference Gapless5.js and Gapless5.css. Also, create a <div> or <span> element where you want the player to appear. Give it a particular id.

<link href="gapless5.css" rel="stylesheet" type="text/css" />
<script src="gapless5.js" language="JavaScript" type="text/javascript"></script>

<!-- then in body: -->
<div id="gapless5-player-id" />

4. Usage

  1. Create a Gapless5 object with an optional parameter object
    • If you want the built-in UI, pass in the element ID as guiId under options.
  2. Add tracks via options in constructor or addTrack()
  3. Optional stuff:
    • Add a cross-fade between tracks using crossfade under options.
      • TIP: try setting this between 25 and 50 ms if you still hear gaps between your tracks. Gap sizes depend on the audio format, browser, etc.
    • Manipulate tracklist with insertTrack(), removeTrack(), and more.
    • Register your own callbacks.
    • Connect key presses to actions using mapKeys() or options in constructor.
const player = new Gapless5({ guiId: 'gapless5-player-id' });

// You can add tracks by relative or absolute URL:

// You can also let the user upload tracks from a file loader like this:
const files = document.getElementById('my-file-input').files;
files.forEach(file => {
  player.addTrack(URL.createObjectURL(file)); // this creates a 'blob://' URL

If you want the user to upload tracks from a file loader, here's an example of that:

  <input type="file" id="my-file-input" accept="audio/*">

4.1. Options

These can be passed into a Gapless5 constructor, or (with the exception of tracks and guiId) set later on the object.

  • guiId
    • id of existing element (i.e. div or span) where you want the player to appear.
    • if empty or not provided, Gapless5 won't use built-in UI.
  • tracks
    • path to audio file(s) or blob URL(s), see examples above
    • can be a single track as a string, an array, or a JSON object containing an array of JSON objects
  • loop
    • default = false
    • loops after end of list/track
  • singleMode
    • default = false
    • plays/loops single track only
  • exclusive
    • default = false
    • stops other Gapless5 players when this one is playing
  • startingTrack
    • default: 0
    • either an array index into the tracks array, or the string random for a random index
  • shuffleButton
    • default = true
    • adds shuffle button to the player UI
  • shuffle
    • default = false
    • enables shuffle mode immediately after playlist load
  • useHTML5Audio
    • default = true
    • if you don't care about immediate playback, set useHTML5Audio to false for lower memory usage
  • useWebAudio
    • default = true
    • if you don't care about gapless playback, set useWebAudio to false for better performance
    • see NOTE below
  • loadLimit
    • default = no limit
    • limits how many tracks can be loaded at once. If you have a large playlist, set to a low number (like 2-5) to save on memory
    • caveat: you will hear gaps/loading delays if you skip tracks quickly enough or jump to arbitrary tracks
    • see NOTE below
  • volume
    • default = 1.0 (0 = silent, 1.0 = loudest)
  • crossfade
    • crossfade duration in milliseconds
    • note: crossfades happen only when transitioning between tracks, not when you start playback
  • crossfadeShape
    • CrossfadeShape.None (default, overlaps both tracks at full volume)
    • CrossfadeShape.Linear
    • CrossfadeShape.EqualPower (curved, louder than linear)
  • playbackRate
    • default = 1.0
    • multiplier for the playback speed, higher = plays faster, lower = plays slower
  • mapKeys
    • pressing specified key (case-insensitive) will trigger any Action function listed above.
  • logLevel
    • minimum logging level (default = LogLevel.Info)
    • set this to LogLevel.Debug for more verbose logging


const player = new Gapless5({
  tracks: ['loop1.mp3', 'loop2.mp3'],
  loop: true,
  loadLimit: 2,
  mapKeys: {prev: 'a', playpause: 's', stop: 'd', next: 'f'},

NOTE 1: if you need audio to keep playing on iOS with Safari in the background, set useWebAudio to false.

NOTE 2: if you use loadLimit with useWebAudio set to false, Safari on iOS may fail to play subsequent tracks. This is due to user interaction requirements, and JS console will show a warning if this happens.

4.2. Functions

You can call these functions on Gapless5 objects.

4.2.1. Parameterized Functions

  • addTrack(audioPath)
    • adds track to end of playlist
    • audioPath: path to audio file(s) or blob URL(s), see examples above
  • insertTrack(index, audioPath)
    • inserts track at location index
    • audioPath: same as in addTrack
  • replaceTrack(index, audioPath)
    • replaces track at location index
    • audioPath: same as in addTrack
  • gotoTrack(indexOrPath)
    • jumps to specified track
    • indexOrPath can be the numerical index, or audio path
  • queueTrack(indexOrPath)
    • similar to gotoPath, but waits for current track to finish first
  • removeTrack(indexOrPath)
    • removes specified track from playlist
    • indexOrPath can be the numerical index, or audio path
  • setPosition(position)
    • updates the current position (in milliseconds)
  • setVolume(volume)
    • updates the volume in real time (between 0 and 1)
  • setCrossfade(duration)
    • sets the crossfade duration in milliseconds
  • setCrossfadeShape(shape)
    • sets the crossfade curve shape
  • setPlaybackRate(playbackRate)
    • updates the playback speed in real time (see playbackRate option)
  • mapKeys(jsonMapping)
    • pressing specified key (case-insensitive) will trigger any Action function listed below.
    • jsonMapping maps an action to a key, see example code below

4.2.2. Accessors

  • isShuffled()
    • returns true if shuffled
  • getTracks()
    • returns list of audioPaths in play order
    • if shuffled, the shuffled order will be reflected here
  • getTrack()
    • returns current track's audioPath ('' if unavailable)
  • getIndex()
    • returns current index in the playlist (-1 if unavailable)
  • getPosition()
    • returns current play position in milliseconds
  • getSeekablePercent()
    • returns percent of current track that's seekable (0-1)
  • findTrack(audioPath)
    • returns index of track in playlist

4.2.3. Actions

All actions can be mapped to keys via mapKeys.

These correspond to built-in UI buttons

  • prev(): matches behavior of "prev" button (scrubs to start if you've progressed into a track)
  • playpause(): matches behavior of "play/pause" button
  • stop(): matches behavior of "stop" button
  • toggleShuffle(): switches between shuffled and un-shuffled
    • subsequent shuffles will be different each time
  • next(): matches behavior of "next" button

These do not correspond to built-in UI buttons

  • prevtrack(): unlike "prev" button, this will always jump to the previous track
  • cue(): play from start
  • play(): non-togglable "play"
  • pause(): non-togglable "pause"
  • shuffle(preserveCurrent = true): non-togglable shuffle, re-shuffles if previously shuffled
    • if preserveCurrent is false, it will shuffle all tracks (without preserving current track)
  • removeAllTracks(): clears entire playlist


player.mapKeys({cue: '7', stop: '8', next: '9'});


// indexes start at 0
player.replaceTrack(0, 'audio/song1_alt.flac');
player.insertTrack(1, 'audio/transition.wav');

player.gotoTrack('audio/song1_alt.flac'); // can also goto track by path

player.removeTrack('audio/transition.wav'); // can also remove track by path

4.3. Callbacks

You can set these on a Gapless5 object. All callbacks include the affected track's audio path except where indicated.

// audio position has changed
ontimeupdate = (current_track_time: number, current_track_index: number) => void

// play requested by user
onplayrequest = (track_path: string) => void

// play actually starts
onplay = (track_path: string) => void 

// play is paused
onpause = (track_path: string) => void

// play is stopped
onstop = (track_path: string) => void

// prev track, where:
//   from_track = track that we're switching from
//   to_track = track that we're switching to
onprev = (from_track: string, to_track: string) => void

// next track, where:
//   from_track = track that we're switching from
//   to_track = track that we're switching to
onnext = (from_track: string, to_track: string) => void

// loading started
onloadstart = (track_path: string) => void 

// loading completed
//   fully_loaded = true for WebAudio data, false for HTML5 Audio data
//   NOTE: this triggers twice per track when both WebAudio and HTML5 are enabled
onload = (track_path: string, fully_loaded: boolean) => void

// track unloaded (to save memory)
onunload = (track_path: string) => void

// track failed to load or play
onerror = (track_path: string, error?: Error | string) => void

// track finished playing
onfinishedtrack = (track_path: string) => void

// entire playlist finished playing
onfinishedall = () => void


function nextCallback(from_track, to_track) {
  console.log(`User skipped to next track (from ${from_track} to ${to_track})`);

const player = new Gapless5({guiId: 'gapless5-player-id', tracks: ['track1.mp3', 'track2.mp3']});
player.onnext = nextCallback;
player.onplay = function (track_path) { console.log(`Now playing ${track_path}`); };

4.4. GUI Customization

While Gapless provides its own GUI, you can also customize it in CSS, or even create your own spans of text controlled by Gapless5.

  • .g5positionbar by class will affect the entire text above all Gapless5 players on your page
  • #g5positionbar-[ID] by id (where [ID] of the guiId you provided) will also customize the entire text for the current player
  • a span with #g5position-[ID] will be set to the current position (e.g. "04:04.95")
  • a span with #g5duration-[ID] will be set to the track's duration
  • a span with #g5index-[ID] will be set to the track's index in the playlist
  • a span with #g5numtracks-[ID] will be set to the number of tracks in the playlist
  • a span with #g5trackname-[ID] will be set to the current track name (filename without extension)

Example: in CSS, hide the built-in gapless5 text:

  #g5positionbar-MyID {
    display: none;

and then create your own elements to be controlled by Gapless5:

  Now Playing: <span id="#g5trackname-MyID"><span> 
  (<span id="#g5position-MyID"><span>)

See an example of customized player text here.

5. License

Licensed under the MIT License.

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