audio-mixer/src/input.ts

Allows mixing of PCM audio streams.

import { Writable, WritableOptions } from 'stream';
import { Mixer } from './mixer';

import * as _ from 'underscore';

export interface InputArguments extends WritableOptions {
    channels?: number;
    bitDepth?: number;
    sampleRate?: number;
    volume?: number;
    clearInterval?: number;
}

export class Input extends Writable {

    private mixer: Mixer;
    private args: InputArguments;

    private buffer: Buffer;
    private sampleByteLength: number;

    private readSample;
    private writeSample;

    public hasData: boolean;

    public lastDataTime: number;
    public lastClearTime: number;

    constructor(args: InputArguments) {
        super(args);

        if (args.channels !== 1 && args.channels !== 2) {
            args.channels = 2;
        }

        if (args.sampleRate < 1) {
            args.sampleRate = 44100;
        }

        if (args.volume < 0 || args.volume > 100) {
            args.volume = 100;
        }

        if (args.channels === 1) {
            this.readMono = this.read;
        }

        if (args.channels === 2) {
            this.readStereo = this.read;
        }

        this.buffer = new Buffer(0);

        if (args.bitDepth === 8) {
            this.readSample = this.buffer.readInt8;
            this.writeSample = this.buffer.writeInt8;

            this.sampleByteLength = 1;
        } else if (args.bitDepth === 32) {
            this.readSample = this.buffer.readInt32LE;
            this.writeSample = this.buffer.writeInt32LE;

            this.sampleByteLength = 4;
        } else {
            args.bitDepth = 16;

            this.readSample = this.buffer.readInt16LE;
            this.writeSample = this.buffer.writeInt16LE;

            this.sampleByteLength = 2;
        }

        this.args = args;
        this.hasData = false;

        this.lastClearTime = new Date().getTime();
    }

    public setMixer(mixer: Mixer) {
        this.mixer = mixer;
    }

    /**
     * Reads the specified number of samples into a buffer
     * @param samples The number of samples to read
     */
    public read(samples) {
        let bytes = samples * (this.args.bitDepth / 8) * this.args.channels;
        if (this.buffer.length < bytes) {
            bytes = this.buffer.length;
        }

        let sample = this.buffer.slice(0, bytes);
        this.buffer = this.buffer.slice(bytes);

        for (let i = 0; i < sample.length; i += 2) {
            sample.writeInt16LE(Math.floor(this.args.volume * sample.readInt16LE(i) / 100), i);
        }

        return sample;
    }

    /**
     * Reads the specified number of samples into a mono buffer
     * This function will be overridden by this.read, if input already is mono.
     * @param samples The number of samples to read
     */
    public readMono(samples) {
        let stereoBuffer = this.read(samples);
        let monoBuffer = new Buffer(stereoBuffer.length / 2);

        let availableSamples = this.availableSamples(stereoBuffer.length);

        for (let i = 0; i < availableSamples; i++) {
            let l = this.readSample.call(stereoBuffer, i * this.sampleByteLength * 2);
            let r = this.readSample.call(stereoBuffer, (i * this.sampleByteLength * 2) + this.sampleByteLength);

            this.writeSample.call(monoBuffer, Math.floor((l + r) / 2), i * this.sampleByteLength);
        }

        return monoBuffer;
    }

    /**
     * Reads the specified number of samples into a stereo buffer
     * This function will be overridden by this.read, if input already is stereo.
     * @param samples The number of samples to read
     */
    public readStereo(samples) {
        let monoBuffer = this.read(samples);
        let stereoBuffer = new Buffer(monoBuffer.length * 2);

        let availableSamples = this.availableSamples(monoBuffer.length);

        for (let i = 0; i < availableSamples; i++) {
            let m = this.readSample.call(monoBuffer, i * this.sampleByteLength);

            this.writeSample.call(stereoBuffer, m, i * this.sampleByteLength * 2);
            this.writeSample.call(stereoBuffer, m, (i * this.sampleByteLength * 2) + this.sampleByteLength);
        }

        return stereoBuffer;
    }

    /**
     * Gets the number of available samples in the buffer
     * @param length The length to get the number of samples for
     */
    public availableSamples(length?: number) {
        length = length || this.buffer.length;

        return Math.floor(length / ((this.args.bitDepth / 8) * this.args.channels));
    }

    /**
     * The method that gets called when this stream is being written to
     */
    public _write(chunk, encoding, next) {
        if (!this.hasData) {
            this.hasData = true;
        }

        this.buffer = Buffer.concat([this.buffer, chunk]);
        next();
    }

    /**
     * Sets the volume of this input
     * @param volume The volume
     */
    public setVolume(volume: number) {
        this.args.volume = Math.max(Math.min(volume, 100), 0);
    }

    /**
     * Gets the current volume for this input
     */
    public getVolume() {
        return this.args.volume;
    }

    /**
     * Clears the buffer but keeps 1024 samples still in the buffer to avoid a possible empty buffer
     */
    public clear(force?: boolean) {
        let now = new Date().getTime();

        if (force || (this.args.clearInterval && now - this.lastClearTime >= this.args.clearInterval)) {
            let length = 1024 * (this.args.bitDepth / 8) * this.args.channels;
            this.buffer = this.buffer.slice(0, length);

            this.lastClearTime = now;
        }
    }

    /**
     * Clears the buffer
     */
    public destroy() {
        this.buffer = new Buffer(0);
    }
}