title: Difference between YUV420 and YUV422
body: <p>Can you please help me understand what are the differences between YUV420 and YUV422 format?
  I read this, <a href="http://www.fourcc.org/yuv.php">http://www.fourcc.org/yuv.php</a>, but I can't find the difference.</p>
  
  <p>And does "YUV420" and "YUV420 SP" mean the same thing?
  And does "YUV422" and "YUV422 I" mean the samet thing?</p>
  
  <p>Thank you.</p>