title: FFmpeg multicast packet filtering with UDP
body: <p><strong>Problem Scenario:</strong><br>
  I am trying to capture <em>multiple</em> multicast cameras on a network with FFmpeg. Upon receiving the streams, I find that each FFmpeg instance running is receiving and decoding the packets destined for the other instances. This causes the video of each instance to flicker between the correct image and the images of all the other cameras. Each camera uses the same destination UDP port and I believe this is the reason its happening.</p>
  
  <p><strong>Example</strong><br>
  Process 1</p>
  
  <pre><code>ffmpeg -rtsp_transport udp_multicast -i "rtsp://192.168.1.1/stream1m" test1.mp4
  </code></pre>
  
  <p>Process 2</p>
  
  <pre><code>ffmpeg -rtsp_transport udp_multicast -i "rtsp://192.168.1.2/stream1m" test2.mp4
  </code></pre>
  
  <p><strong>Expected Output</strong><br>
  Each MP4 contains only one, non-interrupted stream</p>
  
  <p><strong>Actual Output</strong><br>
  As described above</p>
  
  <p>I've trawled through FFmpeg's docs, as well as extensive 'googling' however I can only see a way to filter incoming packets when using an rtp:// or udp:// input. This isn't possible in this application as I want to use RTSP for the SDP it provides.</p>
  
  <p>Any help is greatly appreciated!</p>