Is there any way to save a dirty canvas?

Question

I am making screenshots of videos with HTML5 canvas, the video is hosted elsewhere, everything works except toDataURL() because the canvas is dirty. So, I am wondering, is ther

Answer 1

What about, I haven't tried it yet, if you redraw the original canvas on another canvas which you then save to an image. (and use css or position the canvases over each other to "hide" the second canvas).

Will the second canvas be dirty?

(thinking about a technique like thisone)