title: About youtube-dl
body: <p>As you all know, youtube-dl can download videos from youtube.com. Usually we use the directive e.g. <code>youtube-dl -f 266+140 www.youtube.com/xxxxxx</code>. Then youtube-dl will download the 266(only video) and 140(only audio) individually and then merge them with a wink. </p>
  
  <p>However, recently when I download a 4K HD video, the quality of the analyised audio only have 128kps. But I have the same audio at 320kps. I've tried only download the video without audio and use the ffmpeg to merge them. But the speed was so slow far less than the normal download ways.(266+140) So here comes the question, how can I use the youtube-dl and the ffmpeg to merge my video and 320kps audio quickly just like youtube-dl did?</p>