title: recording sound from webcam using ffmpeg
body: <p>Using <code>ffmpeg arecord -L</code>, I am able to identify my Logitech usb webcam as:</p>
  
  <pre><code>hw:CARD=U0x46d0x821,DEV=0
      USB Device 0x46d:0x821, USB Audio
      Direct hardware device without any conversions
  plughw:CARD=U0x46d0x821,DEV=0
      USB Device 0x46d:0x821, USB Audio
      Hardware device with all software conversions
  </code></pre>
  
  <p>when I go into <code>/dev/snd/by-id</code>, the webcam is described as:</p>
  
  <pre><code>usb-046d_0821_6813BFD0-00 -&gt; ../controlC1
  </code></pre>
  
  <p>I know that the command to use a sound device in ffmpeg is</p>
  
  <pre><code>ffmpeg -f alsa -i $ALSA_DEVICE_NAME..
  </code></pre>
  
  <p>I have tried</p>
  
  <pre><code>ffmpeg -f alsa -i "hw:CARD=U0x46d0x821,DEV=0"
  </code></pre>
  
  <p>and</p>
  
  <pre><code>ffmpeg -f alsa  -i "plughw:CARD=U0x46d0x821,DEV=0"
  </code></pre>
  
  <p>and in both cases I receive the same error message:</p>
  
  <pre><code>ALSA lib pcm.c:2208:(snd_pcm_open_noupdate) Unknown PCM hw=CARD=U0x46d0x821,DEV=0
  [alsa @ 0x9c96580] cannot open audio device hw=CARD=U0x46d0x821,DEV=0 (No such file or directory)
  hw:CARD=U0x46d0x821,DEV=0: Input/output error
  </code></pre>
  
  <p>I have also tried:</p>
  
  <pre><code>ffmpeg -f alsa -i "usb-046d_0821_6813BFD0-00"
  </code></pre>
  
  <p>and</p>
  
  <pre><code>ffmpeg -f alsa -i "usb-046d_0821_6813BFD0-00,DEV=0"
  </code></pre>
  
  <p>and have still received error message</p>
  
  <p>Could you please help in formulating the correct format of the command</p>