title: Coding a certain MP4 GOP with FFMPEG
body: <p>I have a .y4m video file, and I want to convert it to .mp4 using FFmpeg. The problem is that I want a certain kind of GOP, this one: <code>IBBPBBPBBPBB</code>. But what I get, when I set the GOP size to 12 (<code>-g 12</code>) is <code>IPPPPPPPPPPP</code>. I've also tried using the <code>-bf 8</code> option, but I get results like IPBBB... and the video doesn't play right.</p>
  
  <p>Could you please tell me how to get the exact <code>IBBPBBPBBPBB</code> GOP using FFmpeg?</p>
  
  <p>Thanks for your help</p>