如何使用drawImage（）方法在画布上绘制iframe？

Question

到目前为止，这是我的代码：

  function makeIt() {
      var v = document.getElementById('v');
      var canvas = document.getElementById('c');
      var context = canvas.getContext('2d');

      var cw = Math.floor(canvas.clientWidth / 100);
      var ch = Math.floor(canvas.clientHeight / 100);
      canvas.width = cw;
      canvas.height = ch;
      draw(this,context,cw,ch);
  }

  function draw(v,c,w,h) {
      if(v.paused || v.ended) return false;
      c.drawImage(v,0,0,w,h);
      setTimeout(draw,20,v,c,w,h);
  }

但是我得到了错误

TypeError: Argument 1 of CanvasRenderingContext2D.drawImage could not be converted to any of: HTMLImageElement, SVGImageElement, HTMLCanvasElement, HTMLVideoElement, ImageBitmap.[Learn More]

如何将iframe中显示的内容复制到单独的画布上？