aolsenjazz/feeder-node

import { create } from "@alexanderolsen/libsamplerate-js";

/** Port send data directly to audio thread */
let backendPort = undefined;
let resampler;

self.onmessage = async function (e) {
    if (e.data.command == "feed") {
        feed(e.data.data);
    } else if (e.data.command === "connect") {
        // if using AudioWorklet as well, send data directly from this thread to Audio thread
        backendPort = e.ports[0];
    } else if (e.data.command === "init") {
        // this should be called immediately after loading this Worker
        let converterType = e.data.converterType;
        let nChannels = e.data.nChannels;
        let inputSampleRate = e.data.inputSampleRate;
        let outputSampleRate = e.data.outputSampleRate;
        let pathToWasm = e.data.pathToWasm;

        await init(
            converterType,
            nChannels,
            inputSampleRate,
            outputSampleRate,
            pathToWasm
        );
        postMessage({ command: "postInit" });
    } else {
        throw "received unrecognized command";
    }
};

/**
 * Resamples data and sends it to the backend for propagation
 *
 * @param { Float32Array } data Mono or interleaved audio data
 */
function feed(data) {
    let interleaved = new Float32Array(data);
    let resampled = resampler.full(interleaved);

    if (backendPort == undefined) {
        postMessage(resampled, [resampled.buffer]);
    } else {
        backendPort.postMessage({ command: "feed", data: resampled }, [
            resampled.buffer,
        ]);
    }
}

/**
 * Load the sample rate converter WASM module and make it accessible module-wide
 *
 */
async function init(
    converterType,
    nChannels,
    inputSampleRate,
    outputSampleRate,
    wasmPath
) {
    resampler = await create(nChannels, inputSampleRate, outputSampleRate, {
        converterType: converterType,
        wasmPath: wasmPath,
    });
}