Added Opus stream support, added volume interface (#1102)

* Added opus stream support, added volume interface

* Remove setImmediate

* Fix weird syntax error

* Most useless commit ever

You're welcome, @PgBiel

* Fix potential memory leak with OpusScript

Emscripten has the tendency to not free resources even when the Opus engine instance has been garbage collected. Thanks to @abalabahaha for pointing this out.

* Typo

* VoiceReceiver.destroy: destroy opus encoder

src/client/voice/util/VolumeInterface.js

@@ -0,0 +1,57 @@
+const EventEmitter = require('events');
+
+class VolumeInterface extends EventEmitter {
+  constructor({ volume = 0 } = {}) {
+    super();
+    this.setVolume(volume || 1);
+  }
+
+  applyVolume(buffer, volume) {
+    volume = volume || this._volume;
+    if (volume === 1) return buffer;
+
+    const out = new Buffer(buffer.length);
+    for (let i = 0; i < buffer.length; i += 2) {
+      if (i >= buffer.length - 1) break;
+      const uint = Math.min(32767, Math.max(-32767, Math.floor(volume * buffer.readInt16LE(i))));
+      out.writeInt16LE(uint, i);
+    }
+
+    return out;
+  }
+
+  /**
+   * Sets the volume relative to the input stream - i.e. 1 is normal, 0.5 is half, 2 is double.
+   * @param {number} volume The volume that you want to set
+   */
+  setVolume(volume) {
+    this._volume = volume;
+  }
+
+  /**
+   * Set the volume in decibels
+   * @param {number} db The decibels
+   */
+  setVolumeDecibels(db) {
+    this.setVolume(Math.pow(10, db / 20));
+  }
+
+  /**
+   * Set the volume so that a perceived value of 0.5 is half the perceived volume etc.
+   * @param {number} value The value for the volume
+   */
+  setVolumeLogarithmic(value) {
+    this.setVolume(Math.pow(value, 1.660964));
+  }
+
+  /**
+   * The current volume of the broadcast
+   * @readonly
+   * @type {number}
+   */
+  get volume() {
+    return this._volume;
+  }
+}
+
+module.exports = VolumeInterface;