<div class="wrapper">
    <video class="flex" width="765" height="430" src="../" loop controls></video>
    <div class="speed">
      <div class="speed-bar">1×</div>
    </div>
  </div>

			
	

			
	
			

		
	

			
					  const speed = document.querySelector('.speed');
  const bar = speed.querySelector('.speed-bar');
  const video = document.querySelector('.flex');

  function handleMove(e) {
      const y = e.pageY - this.offsetTop;
      const percent = y / this.offsetHeight;
      const min = 0.4;
      const max = 4;
      const height = Math.round(percent * 100) + '%';
      const playbackRate = percent * (max - min) + min;
      bar.style.height = height;
      bar.textContent = playbackRate.toFixed(2) + '×';
      video.playbackRate = playbackRate;
    }

  speed.addEventListener('mousemove', handleMove);