Add ability to set input stream

lib/twilio/audiohelper.ts

@@ -317,6 +317,15 @@ class AudioHelper extends EventEmitter {
         'Related BugZilla thread: https://bugzilla.mozilla.org/show_bug.cgi?id=1299324'));
   }
 
+  /**
+   * Replace the current input steamd with a new MediaStream.
+   * @param stream - A media stream to use as input
+   * @param device - A device to use as input
+   */
+  setInputStream(stream: MediaStream, device: MediaDeviceInfo | null): Promise<void> {
+    return this._setInputStream(stream, device);
+  }
+
   /**
    * Unset the MediaTrackConstraints to be applied on every getUserMedia call for new input
    * device audio. The returned Promise resolves when the media is successfully reacquired,
@@ -487,14 +496,23 @@ class AudioHelper extends EventEmitter {
 
     const constraints = { audio: Object.assign({ deviceId: { exact: deviceId } }, this.audioConstraints) };
     return this._getUserMedia(constraints).then((stream: MediaStream) => {
-      return this._onActiveInputChanged(stream).then(() => {
-        this._replaceStream(stream);
-        this._inputDevice = device;
-        this._maybeStartPollingVolume();
-      });
+      return this._setInputStream(stream, device);
     });
   }
 
+  /**
+   * Replace the current input steamd with a new MediaStream.
+   * @param stream - A media stream to use as input
+   * @param device - A device to use as input
+   */
+   private _setInputStream(stream: MediaStream, device: MediaDeviceInfo | null): Promise<void> {
+    return this._onActiveInputChanged(stream).then(() => {
+      this._replaceStream(stream);
+      this._inputDevice = device;
+      this._maybeStartPollingVolume();
+    });
+ }
+
   /**
    * Update the available input and output devices
    */