Add ability to set stream audio playing in background

src/node/StreamWindow.js

@@ -257,6 +257,10 @@ export default class StreamWindow extends EventEmitter {
     }
   }
 
+  setViewBackgroundListening(viewIdx, listening) {
+    this.sendViewEvent(viewIdx, listening ? 'BACKGROUND' : 'UNBACKGROUND')
+  }
+
   setViewBlurred(viewIdx, blurred) {
     this.sendViewEvent(viewIdx, blurred ? 'BLUR' : 'UNBLUR')
   }

src/node/index.js

@@ -270,6 +270,8 @@ async function main() {
   const onMessage = async (msg, respond) => {
     if (msg.type === 'set-listening-view') {
       streamWindow.setListeningView(msg.viewIdx)
+    } else if (msg.type === 'set-view-background-listening') {
+      streamWindow.setViewBackgroundListening(msg.viewIdx, msg.listening)
     } else if (msg.type === 'set-view-blurred') {
       streamWindow.setViewBlurred(msg.viewIdx, msg.blurred)
     } else if (msg.type === 'set-custom-streams') {

src/node/viewStateMachine.js

@@ -141,6 +141,8 @@ const viewStateMachine = Machine(
                 on: {
                   MUTE: '.muted',
                   UNMUTE: '.listening',
+                  BACKGROUND: '.background',
+                  UNBACKGROUND: '.muted',
                 },
                 states: {
                   muted: {
@@ -149,6 +151,13 @@ const viewStateMachine = Machine(
                   listening: {
                     entry: 'unmuteAudio',
                   },
+                  background: {
+                    on: {
+                      // Ignore normal audio swapping.
+                      MUTE: {},
+                    },
+                    entry: 'unmuteAudio',
+                  },
                 },
               },
               video: {