title: What is a 'VOP' in MPEG-4 (RTP)?
body: <p>I am reading through the MPEG-4 RTP Packet RFC (<a href="http://www.rfc-editor.org/rfc/rfc3016.txt" rel="nofollow">http://www.rfc-editor.org/rfc/rfc3016.txt</a>) and finding very often the word</p>
  
  <p>VOP</p>
  
  <p>I have not found any definition in the net or RFC, does anyone can tell me what this VOP is?</p>