Decodes WAV audio to samples (plus image/video metadata probes) and derives deterministic analysis — beat markers, onsets, waveform — that scenes can sync to.

Install this directly when a scene needs decoded audio or beat/onset analysis. If you're starting a new project, start with the liteship package instead — it brings the whole stack.

Install

pnpm add @czap/assets effect@4.0.0-beta.32

effect v4 is a required peer and only ships as a beta — install the pin above (any >=4.0.0-beta.0 satisfies it).

30 seconds

import { readFile } from 'node:fs/promises';
import { defineAsset, audioDecoder, detectBeats } from '@czap/assets';

// Register the asset once — scenes reference it by id via AssetRef('intro-bed').
defineAsset({
  id: 'intro-bed',
  source: 'audio/intro-bed.wav',
  kind: 'audio',
  budgets: { decodeP95Ms: 50 }, // decode-time budget, in milliseconds
  invariants: [],
});

const file = await readFile('audio/intro-bed.wav');
const audio = await audioDecoder(new Uint8Array(file).buffer);
const { bpm, beats } = detectBeats(audio);
console.log(`${Math.round(bpm)} bpm, ${beats.length} beats`);

Logs the tempo estimate and beat count for the file. beats are sample indices, not milliseconds — @czap/scene provides resolveBeatProjectionToSceneBeats to convert them to timeline time. Same input, same output, every run: the analysis has no randomness, so results are cacheable by content.

Where it sits

A layered package: defineAsset wraps each declaration in a capsule (a declared unit carrying budgets and invariant checks) via @czap/core, and the analysis output shapes come from @czap/_spine so @czap/scene can consume them without depending on this package. The image and video decoders probe format/dimension metadata only — frame decoding belongs to the render pipeline, not here. Test-only registry helpers ship at the @czap/assets/testing subpath. See the package surfaces map for the full layout.