audio-mixer/src/mixer.ts

Allows mixing of PCM audio streams.

import { Input, InputArguments } from './input';
import { Readable, ReadableOptions } from 'stream';

import * as _ from 'underscore';

export interface MixerArguments extends ReadableOptions {
    channels: number;
    sampleRate: number;
    bitDepth?: number;
}

export class Mixer extends Readable {

    protected args: MixerArguments;
    protected inputs: Input[];

    protected sampleByteLength: number;

    protected readSample;
    protected writeSample;
    protected needReadable: boolean = true;

    private static INPUT_IDLE_TIMEOUT = 250;
    private _timer:any = null

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

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

        let buffer = new Buffer(0);

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

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

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

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

            this.sampleByteLength = 2;
        }

        this.args = args;
        this.inputs = [];
    }

    /**
     * Called when this stream is read from
     */
    public _read() {
        let samples = this.getMaxSamples();

        if (samples > 0 && samples !== Number.MAX_VALUE) {
            let mixedBuffer = new Buffer(samples * this.sampleByteLength * this.args.channels);

            mixedBuffer.fill(0);

            this.inputs.forEach((input) => {
                if (input.hasData) {
                    let inputBuffer = this.args.channels === 1 ? input.readMono(samples) : input.readStereo(samples);

                    for (let i = 0; i < samples * this.args.channels; i++) {
                        let sample = this.readSample.call(mixedBuffer, i * this.sampleByteLength) + Math.floor(this.readSample.call(inputBuffer, i * this.sampleByteLength) / this.inputs.length);
                        this.writeSample.call(mixedBuffer, sample, i * this.sampleByteLength);
                    }
                }
            });

            this.push(mixedBuffer);
        } else if(this.needReadable) {
            clearImmediate(this._timer)
            this._timer = setImmediate(this._read.bind(this));
        }

        this.clearBuffers();
    }

    /**
     * Adds an input to this mixer
     * @param args The input's arguments
     */
    public input(args: InputArguments, channel?: number) {
        let input = new Input({
            channels: args.channels || this.args.channels,
            bitDepth: args.bitDepth || this.args.bitDepth,
            sampleRate: args.sampleRate || this.args.sampleRate,
            volume: args.volume || 100,
            clearInterval: args.clearInterval
        });

        this.addInput(input, channel);

        return input;
    }

    /**
     * Removes the specified input
     * @param input The input
     */
    public removeInput(input: Input) {
        this.inputs = _.without(this.inputs, input);
    }

    /**
     * Adds the specified input to this mixer
     * @param input The input
     */
    public addInput(input: Input, channel?: number) {
        if (channel && (channel < 0 || channel >= this.args.channels)) {
            throw new Error("Channel number out of range");
        }

        input.setMixer(this);

        this.inputs[channel || this.inputs.length] = input;
    }

    /**
     * Removes all of the inputs
     */
    public destroy() {
        this.inputs = [];
    }

    public close(){
        this.needReadable = false
    }

    /**
     * Gets the max number of samples from all inputs
     */
    protected getMaxSamples() {
        let samples = Number.MAX_VALUE;

        this.inputs.forEach((input) => {
            let ias = input.availableSamples();

            if (ias > 0) {
                input.lastDataTime = new Date().getTime();
            } else if (ias <= 0 && new Date().getTime() - input.lastDataTime >= Mixer.INPUT_IDLE_TIMEOUT) {
                input.hasData = false;

                return;
            }

            if (input.hasData && ias < samples) {
                samples = ias;
            }
        });

        return samples;
    }

    /**
     * Clears all of the input's buffers
     */
    protected clearBuffers() {
        this.inputs.forEach((input) => {
            input.clear();
        });
    }
}