Simple add following script on your page and create app_id from google console and replace it with hash symbol.
<div id="placeholder-div"></div>
<script>
window.___gcfg = {
lang: 'en-US'
};
(function() {
var po = document.createElement('script'); po.type = 'text/javascript'; po.async = true;
po.src = 'https://apis.google.com/js/platform.js?onload=renderButton';
var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(po, s);
})();
function renderButton(){
gapi.hangout.render('placeholder-div', {
'render': 'createhangout',
'hangout_type' :'onair',
'initial_apps': [
{ app_id : '############', start_data : 'dQw4w9WgXcQ', 'app_type' : 'ROOM_APP' }
]
});
}
</script>