title: ffmpeg error: cur_dts is invalid
body: <p>I'm trying to record video and audio from my webcam with the following command:</p>
  
  <pre><code>ffmpeg -f v4l2 -input_format mjpeg -s uhd2160 -i /dev/video0 -f pulse -channels 1 -i default video.mpg
  </code></pre>
  
  <p>but it seems to get stuck in some endless loop at the bottom of the output that looks like this:</p>
  
  <pre><code>cur_dts is invalid (this is harmless if it occurs once at the start per stream)
  cur_dts is invalid (this is harmless if it occurs once at the start per stream)
  cur_dts is invalid (this is harmless if it occurs once at the start per stream)
  ...
  </code></pre>
  
  <p>Full output with <code>-report</code> flag enabled: <a href="https://pastebin.com/bV1ePJ2u" rel="noreferrer">https://pastebin.com/bV1ePJ2u</a></p>
  
  <p>I can record video and audio separately just fine:</p>
  
  <pre><code>ffmpeg -f v4l2 -input_format mjpeg -s uhd2160 -i /dev/video0 video.mpg
  ffmpeg -f pulse -channels 1 -i default audio.wav
  </code></pre>
  
  <p>So what could be the problem here? I'm on Ubuntu 16.04 kernel 4.14.1</p>