https://blog.wongcw.com/2020/11/20/%e4%ba%9e%e9%a6%ac%e9%81%9c%e5%ae%a3%e5%b8%83%e6%99%ba%e8%83%bd%e7%9c%bc%e9%8f%a1echo-frames%e5%8d%b3%e5%b0%87%e4%b8%8a%e5%b8%82%ef%bc%8cecho-loop%e5%b0%87%e5%81%9c%e7%94%a2/