title: Why does calling ffmpeg from python block?
body: <p>I tried 3 methods to call ffmpeg from python, but it always blocks and doesn't return any result.</p>
  
  <p>However, if I execute it from shell, it works.</p>
  
  <p>For eg:</p>
  
  <pre><code>/usr/bin/ffmpeg -y  -i /tmp/uploadedfiles/movie8_15_10s.mpg -ar 1600 -ac 1  /tmp/uploadedfiles/movie8_15_10s.mpg.wav
  </code></pre>
  
  <p>this works.</p>
  
  <p>However,</p>
  
  <pre><code> ffmpeg_command = "/usr/bin/ffmpeg -y  -i test.wav testout.wav" 
   f_ffmpeg=os.popen(ffmpeg_command);
  </code></pre>
  
  <p>This makes the python hang.</p>