add rining to outgoing call, convert souds to much smaller m4a

src/views/incoming-call-view.jsx

@@ -12,7 +12,7 @@ import { CALL_STATE_INCOMING_RECEIVED } from '../constants.js';
 import { makeImageUrl } from '../lib/blob-helpers.js';
 import { clipStr } from '../lib/utils.js'
 
-const RING_SOUND = new Audio('audio/call-in.mp3');
+const RING_SOUND = new Audio('audio/call-in.m4a');
 
 export default class IncomingCallView extends React.Component {
   constructor(props) {

src/views/tinode-web.jsx

@@ -31,7 +31,7 @@ import { secondsToTime } from '../lib/strformat.js'
 import { updateFavicon } from '../lib/utils.js';
 
 // Sound to play on message received.
-const POP_SOUND = new Audio('audio/msg.mp3');
+const POP_SOUND = new Audio('audio/msg.m4a');
 
 const messages = defineMessages({
   reconnect_countdown: {