title: How to monitor volume level during ffmpeg capture
body: <p>I capture sound from soundcard, convert it to mp3 and stream to multicast IP. 
  Command looks like: </p>
  
  <pre><code>ffmpeg -f alsa -i hw:0 -async 1 -vn -acodec libmp3lame -ac 1 -ar 44100 -b:a 128k -flush_packets 0 -f mpegts -pes_payload_size 426 -mpegts_start_pid 0x44 udp://233.21.215.101:1234?pkt_size=1316
  </code></pre>
  
  <p>But I need to monitor volume level of capturing. If there is no sound (or noise only) I need to switch to another (reserve) channel. </p>
  
  <p>Can I get volume level in ffmpeg output? How I can do it?</p>
  
  <p>P.S: I can get volume level by "volumedetect" filter but it's not in realtime. I need realtime monitoring.</p>
  
  <p>P.P.S: I run ffmpeg programmatically from my application and can't monitor additional windows (like video frame when I use showvolume filter).</p>