video2.js

var pipWindow;
video.addEventListener('enterpictureinpicture', function(event) {
  pipWindow = event.pictureInPictureWindow;
  console.log(`> Window size is ${pipWindow.width}x${pipWindow.height}`);
  pipWindow.addEventListener('resize', onPipWindowResize);
});

video.addEventListener('leavepictureinpicture', function(event) {
  pipWindow.removeEventListener('resize', onPipWindowResize);
});

function onPipWindowResize(event) {
  console.log(`> Window size changed to ${pipWindow.width}x${pipWindow.height}`);
  // Change video quality based on Picture-in-Picture window size.
}