audio-analysis

name

audio-analysis

description

Read real-time amplitude and 8-band frequency data from any AudioSource, AudioStream, or VideoPlayer entity in a Decentraland SDK7 scene with the AudioAnalysis component. Renderer fills the component each frame; scenes copy values into a plain JS view via readIntoView/tryReadIntoView and drive entity scale, color, lights, materials, particles, or UI from amplitude (overall loudness) and bands[0..7] (low→high frequency bins). Use when the user asks for music visualizers, beat reactivity, audio-reactive scenes, equalizers, dancing lights, scaling cubes that pulse to music, audio-driven materials, or anything that should react to sound. Do NOT use to play sound (see audio-video) or to detect player-emitted audio (this reads only entity-attached AudioSource/AudioStream/VideoPlayer audio).

AudioAnalysis

Real-time audio signal analysis attached to any entity that already has an AudioSource, AudioStream, or VideoPlayer. The renderer analyzes the audio frame buffer and writes results back into the component each tick. Scenes read those results to drive visualizers, beat-reactive geometry, audio-driven lights, etc.

RULE: Requires an audio-emitting component on the same entity

AudioAnalysis does nothing on its own. The entity MUST also have one of: AudioSource, AudioStream, or VideoPlayer. The renderer taps that component's audio frame buffer to compute amplitude/bands. An entity with only AudioAnalysis produces no data.

RULE: Audio must be playing for non-zero output

Values are derived from live audio frames. If the source is paused, muted, or not yet loaded, amplitude and all bands[] stay at 0. There is no "ready" event — start your reactive systems unconditionally, they will simply animate toward 0 while silent.

RULE: Only the Unity explorer implements this

Bevy and the mobile Godot explorer ignore the component (no analysis written). Treat AudioAnalysis as a Unity-explorer-only enhancement and design fallbacks (e.g. a base scale that doesn't depend on amplitude) so the scene still looks reasonable elsewhere.

RULE: Read via readIntoView into a pre-allocated view

readIntoView / tryReadIntoView write into a caller-owned AudioAnalysisView = { amplitude: number, bands: number[] }. Allocate the view once at scene init and reuse it every frame — do not new it inside the system. The bands array MUST be pre-sized to 8.

RULE: Use createAudioAnalysis, not create

Use the helper AudioAnalysis.createAudioAnalysis(entity, mode?, amplitudeGain?, bandsGain?). It pre-fills all required protobuf fields (8 bands + amplitude + mode) with safe defaults. Calling the raw AudioAnalysis.create(entity, {...}) requires you to provide every band/amplitude field manually. Use createOrReplaceAudioAnalysis to overwrite an existing one without throwing.

Import

import {
  AudioAnalysis,
  AudioAnalysisView,
  PBAudioAnalysisMode,
  AudioSource, // or AudioStream / VideoPlayer
  engine,
  Transform,
} from "@dcl/sdk/ecs";
import { Vector3 } from "@dcl/sdk/math";

AudioAnalysisView is a TypeScript type alias (not a component), exported from @dcl/sdk/ecs.

Component fields

Output (filled by the renderer; read in your systems):

Field	Type	Range	Notes
amplitude	number	0..~1 (mode-dep.)	Aggregate signal strength of the current audio frame.
band0	number	0..~1 (mode-dep.)	Lowest frequency bin (sub-bass).
band1..6	number	0..~1 (mode-dep.)	Increasing frequency bins, log-spaced under MODE_LOGARITHMIC.
band7	number	0..~1 (mode-dep.)	Highest frequency bin (treble/air).

Inputs (configure once at create time):

Field	Type	Default	Notes
mode	PBAudioAnalysisMode	MODE_LOGARITHMIC	MODE_RAW = 0 (raw FFT magnitudes) | MODE_LOGARITHMIC = 1 (perceptual log mapping, recommended for visualizers).
amplitudeGain	number? (optional)	5.0 when omitted	Multiplier applied to amplitude. Only used in MODE_LOGARITHMIC.
bandsGain	number? (optional)	0.05 when omitted	Multiplier applied to all 8 bands. Only used in MODE_LOGARITHMIC.

Values are unbounded floats — gains can push them above 1. Clamp or scale in your system if the visual you drive needs 0..1. For typical music at default gains, expect peaks roughly in 0..1 with normal content sitting 0..0.5.

AudioAnalysisView

Read-only convenience shape used by readIntoView / tryReadIntoView:

type AudioAnalysisView = {
  amplitude: number;
  bands: number[]; // length 8 — bands[0] = lowest freq, bands[7] = highest
};

Reading the data

const view: AudioAnalysisView = { amplitude: 0, bands: new Array<number>(8) };

engine.addSystem(() => {
  // Throws if the entity has no AudioAnalysis
  AudioAnalysis.readIntoView(audioEntity, view);

  // Or, defensive variant — returns false if missing, no throw
  // if (!AudioAnalysis.tryReadIntoView(audioEntity, view)) return

  // view.amplitude and view.bands[0..7] are now populated
});

readIntoView(entity, out) — populates out from the latest analysis. Throws if the entity has no AudioAnalysis. tryReadIntoView(entity, out): boolean — same, but returns false instead of throwing when the component is missing.

Common patterns

// 1. Pulse an entity's scale to overall amplitude
const view: AudioAnalysisView = { amplitude: 0, bands: new Array<number>(8) };
engine.addSystem(() => {
  AudioAnalysis.readIntoView(audioEntity, view);
  const t = Transform.getMutable(pulseEntity);
  const s = 1 + view.amplitude * 10; // base 1, gain to taste
  t.scale = Vector3.create(s, s, s);
});

// 2. 8-bar equalizer (one entity per band, scale Y by bands[i])
for (const [entity, _] of engine.getEntitiesWith(VisualBar, Transform)) {
  const i = VisualBar.get(entity).index; // 0..7
  Transform.getMutable(entity).scale = Vector3.create(
    1,
    view.bands[i] * BAR_HEIGHT,
    1
  );
}

// 3. Bass-only kick — react to the lowest band
const bass = view.bands[0] + view.bands[1]; // sub + low
if (bass > 0.7) {
  /* trigger flash */
}

// 4. Custom gains (less sensitive amplitude, punchier bands)
AudioAnalysis.createAudioAnalysis(
  audioEntity,
  PBAudioAnalysisMode.MODE_LOGARITHMIC,
  2.0,
  0.1
);

For a complete music visualizer (audio source + amplitude sphere + 8-band equalizer bars), see {baseDir}/references/audio-analysis-example.md.

Mode selection

• MODE_LOGARITHMIC (default) — bands are log-spaced and gain-scaled to roughly fit 0..1 for typical music. Use this for visualizers, scaling, color reactivity. amplitudeGain and bandsGain apply.
• MODE_RAW — raw FFT-derived magnitudes, linearly spaced. Lower bands dominate visually because most musical energy is there. amplitudeGain / bandsGain are ignored. Use only if you intend to do your own normalization.

Gotchas

• **Component ID is 1212
• amplitudeGain and bandsGain are no-ops in MODE_RAW. Setting them won't error, but the renderer ignores them outside MODE_LOGARITHMIC.
• Output values can exceed 1.0 with high gains or loud source material. Clamp downstream if you feed UI bars or alpha channels expecting 0..1.
• Throttled updates. The renderer runs analysis under a frame-time budget — values update each frame in normal conditions but can skip frames under heavy load. Drive smooth animations with dt interpolation rather than assuming a fixed update cadence.
• Multi-source scenes. Each audio-emitting entity needs its own AudioAnalysis if you want to react to that specific source. There is no global mix-down; you pick the entity to analyze.
• Works on VideoPlayer audio too. The renderer's MediaPlayerComponent (which backs both AudioStream and VideoPlayer) implements the same audio frame buffer interface as AudioSource, so you can drive visuals from a video's soundtrack.
• No pitch interaction. AudioSource.pitch changes playback speed; the analysis runs on the actual played audio frames, so a higher pitch shifts perceived band energy upward. This is expected, not a bug.
• Don't call readIntoView before createAudioAnalysis. Reading without the component throws. Use tryReadIntoView if the component may not be attached yet (e.g. analysis added at runtime).

Permissions

No special scene permission is needed beyond what the underlying AudioSource / AudioStream / VideoPlayer already requires. Streamed audio still needs ALLOW_MEDIA_HOSTNAMES in scene.json for its hostname (see audio-video skill).

Example scenes

• audio-visualization — engine-team test scene: AudioSource + AudioAnalysis.createAudioAnalysis() (defaults) on one entity, one readIntoView system feeding a shared view, then separate consumer systems driving 8 equalizer bars from bands[i] and a sphere from amplitude. Matches the canonical pattern documented above.

Resources

• {baseDir}/references/audio-analysis-example.md — full music visualizer scene from the SDK examples (audio source + amplitude pulse + 8-bar equalizer).
• Source PRs: protocol #328, js-sdk-toolchain #1256, unity-explorer #6361.
• Reference scene: sdk7-goerli-plaza/audio-visualization.