title: fps is too low when ffmpeg grab video
body: <p>I use ffmpeg with the following options:</p>
  
  <pre><code>ffmpeg -f video4linux2 -s 640x480 -r 25 -i /dev/video0 http://localhost:8090/feed1.ffm
  </code></pre>
  
  <p>All I want to do is to watch the web live video in my chrome browser. This is relevant part in my ffserver.conf file :</p>
  
  <pre><code>&lt;Stream test.webm&gt;              # Output stream URL definition
     Feed feed1.ffm              # Feed from which to receive video
     Format webm
     NoAudio
      #Audio settings
     #AudioCodec vorbis
     #AudioBitRate 64             # Audio bitrate
  
     # Video settings
     VideoCodec libvpx            
     VideoSize 720*576           # Video resolution 
     VideoFrameRate 25           # Video FPS
     AVOptionVideo flags +global_header  # Parameters passed to encoder
                                         # (same as ffmpeg command-line parameters)
     AVOptionVideo cpu-used 0
     AVOptionVideo qmin 10
     AVOptionVideo qmax 42
     AVOptionVideo quality good
     AVOptionAudio flags +global_header
     PreRoll 15
     StartSendOnKey
     VideoBitRate 400            # Video bitrate
  &lt;/Stream&gt;
  </code></pre>
  
  <p>When I open chrome to the following location:</p>
  
  <pre><code>http://localhost:8090/test.webm
  </code></pre>
  
  <p>I can successfully watch the live video, but due to a low fps, I just doesn't produce a fluent video. I found out that the fps is only around 6. Sometimes it goes up to around 10 or 15. When that is the case, the becomes video a bit more fluent.</p>
  
  <p>I have set the fps to 25, so I wonder why it actually gets to the low fps reate.</p>