Solution #1

My solution here is to create an iframe

<iframe src="https://stackoverflow.com/questions/50490304/audio/source.mp3" allow="autoplay" style="display:none" id="iframeAudio">
</iframe> 

and audio tag aswell for non-chrome browsers

<audio autoplay loop  id="playAudio">
    <source src="https://stackoverflow.com/questions/50490304/audio/source.mp3">
</audio>

and in my script

  var isChrome = /Chrome/.test(navigator.userAgent) && /Google Inc/.test(navigator.vendor);
  if (!isChrome){
      $('#iframeAudio').remove()
  }
  else {
      $('#playAudio').remove() // just to make sure that it will not have 2x audio in the background 
  }

Solution #2:

There is also another workaround for this according to @Leonard

Create an iframe that doesn’t play anything just to trigger the autoplay in the first load.

<iframe src="https://stackoverflow.com/questions/50490304/silence.mp3" allow="autoplay" id="audio" style="display: none"></iframe>

good source for the mp3 file silence.mp3

Then play your real audio file at ease.

<audio id="player" autoplay loop>
    <source src="https://stackoverflow.com/questions/50490304/audio/source.mp3" type="audio/mp3">
</audio>

Personally I prefer solution #2 because it is cleaner approach for not relying so much in JavaScript.

Update August 2019

Solution #3

As an alternative we can use <embed>

For Firefox
It seems that audio auto-play is working so we don’t need the <embed> element because it will create double audio running.

// index.js
let audioPlaying = true,
    backgroundAudio, browser;
browser = navigator.userAgent.toLowerCase();
$('<audio class="audio1" src="https://stackoverflow.com/questions/50490304/audio.mp3" loop></audio>').prependTo('body');
if (!browser.indexOf('firefox') > -1) {
    $('<embed id="background-audio" src="https://stackoverflow.com/questions/50490304/audio.mp3" autostart="1"></embed>').prependTo('body');
    backgroundAudio = setInterval(function() {
        $("#background-audio").remove();
        $('<embed id="background-audio" src="https://stackoverflow.com/questions/50490304/audio.mp3"></embed>').prependTo('body');
    }, 120000); // 120000 is the duration of your audio which in this case 2 mins.
}

Also if you have a toggle event for your audio make sure to remove the created <embed> element for audio.

Note: After your toggle, it will restart from the beginning because the <embed> is already deleted and the <audio> element will play as normal now.

$(".toggle-audio").on('click', function(event) {
    audioPlaying = !audioPlaying;
    $("#background-audio").remove();

    clearInterval(backgroundAudio);
    if (audioPlaying){
        $(".audio1").play();
        // play audio 
    }
    else {
        $(".audio1").pause();
    }

And now make sure to hide these <audio> and <embed> elements

audio, embed {
    position: absolute;
    z-index: -9999;
}

Note: diplay: none and visibility: hidden will make the <embed> element not work.