Use this skill for sound and music in melonJS — loading audio, playing effects, background tracks, audio sprites, volume and muting, spatial audio, procedural tone/noise generation, and effects such a
1---2name: melonjs-audio3description: Use this skill for sound and music in melonJS — loading audio, playing effects, background tracks, audio…4---56# packages/melonjs/skills/melonjs-audio/SKILL.md
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1npx skills add melonjs/melonJS --skill melonjs-audio -a cursor -y
Paste the copied command in a terminal. It installs this SKILL.md into that agent.
Use this skill for sound and music in melonJS — loading audio, playing effects, background tracks, audio sprites, volume and muting, spatial audio, procedural tone/noise generation, and effects such as reverb or a compressor on the whole mix. Covers the mandatory audio.init format list, the directory-not-file src convention, playTrack versus play, the fixed listener and pixel-scale distances of positional sound, and browser autoplay unlocking. Triggers on: audio, sound, audio.init, audio.play, playTrack, stopTrack, audio.load, sfx, music, volume, mute, fade, rate, pitch, sprite audio, stereo, panner, position, listener, refDistance, reverb, echo, delay, compressor, distortion, filter, audio effect, audio.tone, audio.noise, getAudioContext, getMasterGain, hasAudio, hasFormat, autoplay, no sound, sound stopped working, context suspended, silent after idle, clips silent but tones play.
Download packages/melonjs/skills/melonjs-audio/SKILL.md from the publisher, or copy the path and open the repository. PlugMCP lists the skill and does not host the file.
Where does melonjs-audio live?
The publisher keeps it at https://github.com/melonjs/melonJS.
Which agents can use melonjs-audio?
Claude, Cursor, Codex, and Grok Build can read a SKILL.md you add from the publisher's repository. Grok Bot installs it when you send the skill's GitHub folder link in a chat.
From the publisher
SKILL.md
name
melonjs-audio
description
Use this skill for sound and music in melonJS — loading audio, playing effects, background tracks, audio sprites, volume and muting, spatial audio, procedural tone/noise generation, and effects such as reverb or a compressor on the whole mix. Covers the mandatory audio.init format list, the directory-not-file src convention, playTrack versus play, the fixed listener and pixel-scale distances of positional sound, and browser autoplay unlocking. Triggers on: audio, sound, audio.init, audio.play, playTrack, stopTrack, audio.load, sfx, music, volume, mute, fade, rate, pitch, sprite audio, stereo, panner, position, listener, refDistance, reverb, echo, delay, compressor, distortion, filter, audio effect, audio.tone, audio.noise, getAudioContext, getMasterGain, hasAudio, hasFormat, autoplay, no sound, sound stopped working, context suspended, silent after idle, clips silent but tones play.
license
MIT
Audio
Two setup rules
import { audio, loader } from "melonjs";
audio.init("mp3,ogg"); // 1. BEFORE preloading any audio
await loader.preload([
{ name: "cling", type: "audio", src: "data/sfx/" }, // 2. a PREFIX, not a file
]);
audio.init(format) must run before any audio asset is preloaded, and
lists the formats you actually ship. Preloading first throws
target audio extension(s) should be set through me.audio.init() before calling the preloader. It returns false when no audio backend is
available, so it is worth checking. The format list defaults to "mp3".
src is a prefix, not a file. The loader appends the asset name plus
each configured extension and uses the first that loads — so
data/sfx/ + cling + mp3 → data/sfx/cling.mp3. Passing a full filename
gives you a 404. A data:audio/... URL is the one exception: it is used
verbatim, prefix and extension skipped.
audio.hasAudio() says whether the browser can play audio at all, and
audio.hasFormat("ogg") whether it can play one codec — useful for choosing
the init list or hiding a sound toggle on a device with no audio.
Order matters — melonJS tries the listed formats left to right, so put the
preferred one first. Two formats ("webm,mp3" or "mp3,ogg") is the usual
belt-and-braces for codec coverage. Accepted tokens: mp3, mpeg, opus,
ogg, oga, wav, aac, caf, m4a, m4b, mp4, weba, webm, dolby,
flac.
Effects versus music
audio.play("cling"); // fire and forget
audio.play("cling", false, null, 0.5); // loop, onend, volume
const id = audio.play("engine", true); // looping; keep the id to stop it
audio.playTrack("theme"); // background music
audio.stopTrack();
Use playTrack for music, not . always
loops, and it records the name as the current track — which is what
/ / act on, via
→ . , ,
and all read that same single slot, so there
is only ever one current .
play
playTrack(name, volume?)
app.pauseOnBlur
resumeOnFocus
stopOnBlur
state.pause(true)
pauseTrack()
stopTrack()
pauseTrack()
resumeTrack()
getCurrentTrack()
track name
playTrack stops the track it replaces (20.9.0 and later; before that it
only assigned the slot, and the previous bed kept looping underneath where
stopTrack() could no longer reach it). So a scene just states its own music
and nothing cancels anything:
Calling it with the track already playing restarts it, the same as play()
on any other clip. A scene that wants the bed to carry on across a screen
change should not call it again, rather than rely on it doing nothing.
stopTrack() is for where nothing follows: a scene whose successor has no
music of its own, or a game going quiet. state.change destroys the outgoing
stage before it resets the incoming one, so a stopTrack() in
onDestroyEvent and a playTrack() in the next onResetEvent are in that
order and never cancel each other.
To end a track on an event rather than on a screen change, say a run ending
while the player stays on the same screen, audio.fade(name, from, 0, ms)
takes it down gently. A fade to zero is silence, not a stop, so the voice is
still live until something stops it or replaces it.
Every per-clip function throws audio clip <name> does not exist if the clip was
never loaded, and play additionally throws when a named sprite region is
missing.
Audio sprites
One file carrying many effects, with named regions in milliseconds:
An MP3 encoder pads the end of its file. Chrome and Firefox trim the padding when
they decode it, Safari keeps it, so a looping MP3 has a short silence at every
loop there (27 ms on a 12 s clip at 22 kHz, measured). Declare a region of the
loop's exact length and loop on that: the voice never reaches the padding.
The optional third element marks a region as looping: it loops unless play() is
told loop: false (before 20.11 it only looped when loop: true was passed as
well). play()'s second argument
takes either the original loop boolean or a PlayOptions object
(sprite, loop, onend, volume, plus the spatial follow, at and
stopWithTarget) — both forms work. Object fields win over the positional
onend / volume arguments when both are supplied.
Clip state
audio.duration("theme"); // seconds — 0 while still loading
audio.duration("sfx", id); // duration of the region THAT instance plays
audio.playing("theme"); // is anything playing?
audio.playing("theme", id); // is that instance playing?
audio.state("theme"); // "unloaded" | "loading" | "loaded"
stop(), pause() and resume() take an optional instance id too; omit it
and the whole group is affected. audio.stop() with no arguments at all stops
every sound. audio.seek(name) reads the position, audio.seek(name, s, id?)
writes it; audio.rate(name, r, id?) changes speed and pitch together
(0.5..4.0, 1 is normal) and audio.fade(name, from, to, ms, id?) ramps
the volume (0..1, over milliseconds).
Volume and muting
audio.setVolume(0.5); // global, 0..1
audio.getVolume(); // read it back
audio.mute("cling"); // one clip — mute(name, id?, shouldMute = true)
audio.unmute("cling");
audio.muteAll(); // everything (audio.disable() is an alias)
audio.unmuteAll(); // (audio.enable() is an alias)
audio.muted(); // global mute state
audio.unload(name) / audio.unloadAll() free the decoded buffers; unload
also clears the current-track pointer if it named that clip.
Losing focus mutes everything
When the window loses focus the engine mutes all audio, and unmutes it on
focus. That covers sound effects, procedural tone / noise and the mixer
effects, not just the music track that state.pause() pauses. Set
pauseOnBlur: false in the application settings if a clip has to keep playing
in the background.
Spatial audio
audio.position("engine", x, y, z);
audio.orientation("engine", x, y, z);
audio.stereo("engine", -1); // -1 left … 1 right
audio.panner("engine", { coneInnerAngle: 90, /* … */ });
position(name, x, y = 0, z = -0.5, id?) and
orientation(name, x, y, z, id?) both default id to "the whole group".
Called with just the clip name, each of the four returns the current value —
stereo gives 0 and position gives [0, 0, 0] before they have ever been
set.
Let the engine place the sound: follow and at
The shortest path to positional audio is a play option. Both take world
pixels, the same numbers as pos.x / pos.y, and the engine converts to
audio space for you:
// tracks the renderable every frame, and stops when it is destroyed
audio.play("ufo", { follow: this, stopWithTarget: true });
// pinned to a fixed world point
audio.play("portal", { at: { x: 1200, y: 480 } });
follow and at are mutually exclusive: passing both throws, rather than
quietly picking one. follow re-reads the target's absolute position each
frame, so a renderable nested in a moving container is placed correctly. stopWithTarget is what you
want for a sound that belongs to an entity: without it a looping clip on a
destroyed renderable keeps playing from wherever it last was. audio.unfollow(id)
detaches a sound and leaves it playing where it is.
Move the listener, don't do the subtraction yourself
audio.setListener(player); // tracked every frame
audio.listener(x, y, z); // or place it by hand
audio.listener(); // → [x, y, z] in world pixels
audio.listenerOrientation(fx, fy, fz, ux, uy, uz);
audio.setListener(null); // stop tracking
With a listener in the world, source positions are absolute world
coordinates, not offsets. The older idiom — passing source.pos.x - player.pos.x every frame with the ear stuck at the origin — still works, but
only if you leave the listener at (0, 0, 0); mixing the two double-counts the
player's position.
setListener places the ear at the target's absolute position after the world
updates. A plain renderable contributes position only, so a side-scroller keeps
the default "facing into the screen" and gets left-right panning plus distance
falloff from the one call.
A Camera3d target also contributes its orientation, taken from its own
basis, so turning the camera swings the stereo image with it. That is the whole
of what a posed 3D scene needs:
audio.setListener(app.viewport); // in a 3D scene this is a Camera3d
audio.play("drone", { follow: saucer }); // scene coordinates, directly
Y is down. Every one of these calls takes and returns melonJS world
coordinates, where y grows downward; the Y-up flip Web Audio wants happens
inside the engine. Pass pos.y as it is.
The defaults are tuned for pixels
audio.setSpatialDefaults() / getSpatialDefaults() set the panner attributes
a sound placed through follow or at starts from, and the shipped values
assume a 2D game measured in pixels:
attribute
default
refDistance
240
maxDistance
10000
panningModel
"equalpower"
distanceModel
"inverse"
With those, a placed sound is at full volume out to 240 px and then halves
each time the distance doubles: about half at 480, a quarter at 960, roughly
an eighth at 2000. maxDistance is where it stops getting quieter.
They apply to placed sounds only. A plain audio.play() followed by a
bare audio.position() keeps WebAudio's own defaults, where refDistance is
1 METRE and a source 100 px out is already near silent. That path is
unchanged, which is what keeps old code working.
audio.panner(name, attrs, id?) still overrides per clip or per voice, and it
merges over the current values rather than replacing them, so writing one field
no longer resets the rest. Called without an id it writes the group
defaults, which is what a clip-wide tuning call looks like.
For a 3D scene where front-to-back matters, panningModel: "HRTF" is worth the
cost; for a 2D one it mostly muddies the stereo image.
stereo and position: last writer wins
Both drive the same per-instance panner node, and the engine swaps the node to
match whichever you called last: stereo() after position() gives you
plain left-right panning, and position() after stereo() gives you 3D
falloff. Neither silently does nothing any more, and the order you call them in
no longer matters.
Still pick one per voice and stay with it. A 2D game usually wants stereo()
alone; reach for position() (or follow / at) when distance falloff
matters.
Spatial audio is WebAudio-only. On a clip loaded with stream: true (or
html5: true, or preload: false) stereo / position / orientation return early and do
nothing — which is exactly the case for the long music tracks people reach for
first. follow and at are equally inert on a streamed clip.
Procedural sound
For beeps, blips and noise without shipping files. Both take one options
object, and duration (in seconds) is required:
tone also takes wave (default "sine"), attack (0.005) and pitchSlide
(1). noise takes type ("white" | "pink" | "brown", default
"white"), attack, pan, filter and filterSweep. gain defaults to 0.1
on both.
Sequencing: delay, not setTimeout
Both take delay — seconds before the sound starts, scheduled on the audio
clock. That is what builds a multi-part sound: a stinger's second note, an
explosion's double-tap.
Do not reach for setTimeout here. A timer fires on the main thread, so a busy
frame slips the note late and the sequence audibly loses time — the fault is
easy to blame on the sound design rather than the scheduling. delay is
sample-accurate because the whole envelope is scheduled up front.
Both are silent no-ops when there is no WebAudio context — they bail on
getAudioContext() === null rather than throwing. Neither needs the clip to be
loaded; neither goes through the file-playback path at all.
audio.getAudioContext() and audio.getMasterGain() are the escape hatches for
custom Web Audio work; both return null when audio is unavailable, so guard.
Connect a custom graph to the master gain rather than ctx.destination if you
want it to respect setVolume / muteAll.
Effects on all game audio: reverb, echo, compressor
There is no built-in reverb, delay, distortion or compressor, and no per-clip
filter on file playback. There does not need to be one for the common case:
every buffered clip and every tone / noise passes through the master gain
on its way to the speakers, so an effect inserted after it applies to the
whole mix.
const ctx = audio.getAudioContext(); // creates the context if needed
const master = audio.getMasterGain();
if (ctx && master) { // null when audio is unavailable
const comp = ctx.createDynamicsCompressor();
master.disconnect(); // master -> speakers becomes
master.connect(comp); // master -> compressor -> speakers
comp.connect(ctx.destination);
}
Any Web Audio node or chain works the same way: a ConvolverNode with an
impulse response for reverb, a DelayNode with a feedback gain for echo, a
BiquadFilterNode for an underwater low-pass, a WaveShaperNode for
distortion. Do it once, at startup; the master gain lives as long as the
context.
setVolume / muteAll still work, because they act on the master gain,
which is now upstream of the effect.
Streamed clips are not affected. A stream: true (html5: true) clip
plays through an <audio> element and never reaches the master gain — which
is usually the music. Preload the music buffered if it must go through the
effect.
It is all or nothing. The per-instance nodes are not public, so an effect
on one clip only (muffling one sound behind a wall) is not possible through
this route; noise has its own filter for generated sounds.
To remove it, reverse the wiring: master.disconnect(); master.connect(ctx.destination);.
Autoplay: sound is silent until the first gesture
Browsers create the audio context in the suspended state and keep it there
until a user interaction. Nothing errors — audio simply does not play, which
reads as a bug. melonJS installs one-shot touchstart / touchend / click /
keydown unlock listeners on document, so the first real gesture anywhere
unlocks it and fires the clip's on.unlock callback. Design for it: start music
on the first click or key press, not on load. The usual way to guarantee one is
a gate screen — a splash, a "press any key", or a health/photosensitivity notice
— whose dismissal is the gesture, so the menu behind it can start its music
unconditionally. Note the unlock listens for keydown too, so a keyboard-only
player is covered.
The context can stop again, long after it was unlocked
Unlocking is only the first half. A context that has been running can be
stopped later: melonJS suspends it itself after thirty idle seconds to save
power, and browsers stop it for their own reasons, a backgrounded tab among
them. Recovery is automatic and you do not have to write it: a user gesture
or the tab coming back to the front revives it, and a deliberate idle
suspension is left alone so the power saving still works.
The symptom worth memorising, because it points straight at the cause:
if tone and noise are audible while loaded clips are silent, the context
is healthy and the engine's playback state is wrong. The generators only need
a live context, where a clip goes through the engine's state machine and can
be parked waiting for a resume. It is never "the context died".
Both routes ask the same owner to resume, so hearing a tone tells you the
hardware is back; it tells you nothing about whether the clips waiting on the
engine's state have been let go.
That asymmetry was a real Safari-only bug: thirty idle seconds before the
first click left the engine waiting on a suspend the browser never confirmed,
so every clip queued for the life of the page while generated sound played
normally. Fixed in 20.9, and the lesson generalises: a clip that will not play
is a state question, not a hardware one.
Playback also starts asynchronously: play() returns an id while the
instance is still starting, so playing() can legitimately be false on the
very next line.
Load-time options
{ name: "sfx", type: "audio", src: "data/sfx/",
sprite: { jump: [0, 450] },
pool: 5, // finished instances kept for reuse — NOT a concurrency cap
rate: 1.0, // initial playback rate, 0.5..4.0
mute: false,
loop: false,
autoplay: false,
preload: true, // false: fetched on first play, then streamed; or "metadata"
format: "mp3", // explicit hint when the URL has no usable extension
stream: true, // long music: stream rather than decode into memory
on: { play() {}, end() {}, stop() {}, unlock() {} },
}
pool (default 5) is a reuse cap on finished voices, not a limit on
simultaneous playback: when the number of ended voices exceeds it, the surplus
are disconnected and dropped. Raise it for a clip triggered in rapid bursts, not
to allow more overlap.
Use stream: true for long music tracks — it plays through an HTML5 <audio>
element instead of decoding the whole file into memory. (html5: true is the
same switch under its backend name.) on accepts the full lifecycle set:
play, pause, stop, end, fade, seek, rate, volume, mute,
unlock.
preload: false keeps a clip out of the preload. Nothing is downloaded for
it until it is first played (audio.play, audio.playTrack, or autoplay).
That play fetches it and streams it, as stream: true does, so the sound starts
as soon as enough of the file has arrived, not once all of it has; a clip never
played is never downloaded. Use it for music a player may never reach (a boss
theme, the ending) to shorten the wait before the game starts.
The loader reports such a clip done at once: audio.state(name) is
"unloaded" until its first play, then "loading", then "loaded".
It starts with the short delay of a stream on its first play. Keep a sound
effect that must sound the instant it is triggered preloaded.
Being streamed, it has the limits of stream: true: positional sound does
not apply to it, and it ignores withCredentials (see below).
Before 20.12.0 such a clip was never fetched at all, and stayed silent.
stream: true alone still fetches the clip during the preload; combine it with
preload: false to defer that too. preload: "metadata" only matters for a
streamed clip: the preload fetches just enough to know its duration.
Outside a preload, audio.load(asset, onload?, onerror?) takes the same
descriptor and loads one clip at runtime — for a level's sounds fetched when
the level starts. The loader calls the same function, so the same rules apply.
Re-preloading a manifest that already contains a loaded clip is a no-op —
audio.unload(name) first if you genuinely want to reload it.
Credentials work as for every other asset type. Buffered audio on the
game's own origin carries its cookies and HTTP auth with no option; a clip on
another origin behind a login needs loader.setOptions({ withCredentials: true }),
not an audio-specific option, and that server must allow credentials. Buffered
audio fetches through the shared loader path, so it behaves exactly as an image
or a JSON file does. A streamed clip (stream: true, or
preload: false) does not: it plays
through an <audio> element, which needs a crossorigin attribute rather than
fetch credentials. Preload a clip buffered if it sits behind a login.
Failing clips and setStopOnAudioError(false). The default is to fail the
preload when a clip cannot be loaded after its retries: the error reaches the
loader, so await loader.preload(...) rejects and your catch runs, and the
reason is logged. Turn the flag off and the engine mutes audio, warns
(failed loading <name>, disabling audio) and lets the load continue — the
preload finishes and the game reaches the next scene without sound.
Before 20.4 both halves were broken: with the flag off it disabled audio and
failed the preload anyway, and a clip whose bytes arrived but would not decode
(a missing file served as HTML by an SPA rewrite, say) reported nothing at all
either way — blank screen, empty console.
Symptom → cause
symptom
cause
audio assets 404
src given as a full filename instead of a directory prefix
target audio extension(s) should be set... thrown at preload
audio.init() not called before preloading
audio clip X does not exist
the clip was never preloaded, or the name is mis-cased — every per-clip call throws this
nothing plays until the user clicks
browser autoplay policy — expected, design around it
playing() is false right after play()
playback starts asynchronously
music keeps playing after leaving a scene
used play instead of playTrack, or no stopTrack in teardown
two music tracks playing at once, and stopTrack() only silences one
melonJS before 20.9.0: playTrack did not stop the previous track, so the scene that started it had to stopTrack() on the way out
the music restarts when returning to a screen
playTrack with the track already playing restarts it; don't call it again if the bed should carry on
stereo / position do nothing
the clip was loaded with stream: true or preload: false — spatial is WebAudio-only
a preload: false clip never plays, and audio.state() stays "unloaded"
melonJS before 20.12.0 never fetched such a clip; preload it, or update
one format works, another does not
that codec is not in the audio.init() list
audio on another origin behind a login fails, or the preload hangs
loader.setOptions({ withCredentials: true }) — the same switch every asset type uses. Audio on the game's own origin needs nothing (before 20.13 it needed it too)
a streamed clip ignores withCredentials
stream: true plays through an <audio> element; preload it buffered instead
audio.tone(440, {...}) does nothing / errors
tone takes a single options object with a required duration
tone / noise are silent with no error
no WebAudio context — getAudioContext() returned null
a positioned sound is silent, or only audible right next to the player
placed by hand with audio.position(), which keeps WebAudio's metre defaults (refDistance: 1) — use follow / at, or set refDistance in pixels with audio.panner()
a positioned sound does not follow the player
nothing is placing it — audio.play(name, { follow: entity }), and audio.setListener(player) once
a followed sound pans to the wrong side as the player moves
the listener was moved and positions are still relative to the player — with a listener in the world, pass absolute world coordinates
a looping sound outlives the entity that owns it
follow without stopWithTarget: true
a voice panned with stereo() loses its 3D placement, or the reverse
one panner node per voice and last writer wins — pick one per voice and stay with it
a reverb / compressor on the master gain does not affect the music
the music is stream: true, which bypasses the master gain — preload it buffered
a looping MP3 drops out for a moment at every loop, in Safari only
Safari keeps the encoder's padding at the end of the file: loop a sprite region of the clip's exact length (see "A loop with no gap")
sound effects keep playing after the window loses focus
pauseOnBlur and stopOnBlur are both off, so the engine is deliberately leaving the game running in the background
Related skills
melonjs-getting-started — preloading and asset ordering