<button class="btn btn-primary" id="button">Display Webcam feed in Picture-in-Picture mode</button>

body {
  padding: 20px;
}

const button = document.getElementById('button');

button.addEventListener('click', async () => {
  const video= document.createElement('video');
  video.muted = true;
  video.srcObject = await navigator.mediaDevices.getUserMedia({ video: true });
  video.play();
  video.addEventListener('loadedmetadata', () => {
    video.requestPictureInPicture()
    .catch(console.error)
  });
});