feat(IFrameApi): setAudioOnly command & event.

modules/API/API.js

@@ -14,6 +14,7 @@ import {
     requestEnableVideoModeration
 } from '../../react/features/av-moderation/actions';
 import { isEnabledFromState } from '../../react/features/av-moderation/functions';
+import { setAudioOnly } from '../../react/features/base/audio-only/actions';
 import {
     endConference,
     sendTones,
@@ -565,6 +566,10 @@ function initCommands() {
             sendAnalytics(createApiEvent('set.video.quality'));
             APP.store.dispatch(setVideoQuality(frameHeight));
         },
+        'set-audio-only': enable => {
+            sendAnalytics(createApiEvent('set.audio.only'));
+            APP.store.dispatch(setAudioOnly(enable));
+        },
         'start-share-video': url => {
             sendAnalytics(createApiEvent('share.video.start'));
             const id = extractYoutubeIdOrURL(url);
@@ -2218,6 +2223,19 @@ class API {
         });
     }
 
+    /**
+     * Notify the external application (if API is enabled) when the audio only enabled status changed.
+     *
+     * @param {boolean} enabled - Whether the audio only is enabled or not.
+     * @returns {void}
+     */
+    notifyAudioOnlyChanged(enabled) {
+        this._sendEvent({
+            name: 'audio-only-changed',
+            enabled
+        });
+    }
+
     /**
      * Disposes the allocated resources.
      *