title: Can't get MLT Framework to process audio in Docker container
body: <p>I am using Docker to create a container for video processing using the <code>melt</code> command. All videos output at the moment do not include any audio.</p>
  
  <p>Here's the Dockerfile:</p>
  
  <pre><code>FROM ubuntu
  RUN apt-get update
  RUN apt-get install -y melt swh-plugins
  WORKDIR /input
  CMD [ "melt", "input.mp4", "-consumer", "avformat:/output/output.mp4" ]
  </code></pre>
  
  <p>When I run the container, I get the following error:</p>
  
  <pre><code>consumer_avformat.c: Unable to encode audio - disabling audio output.
  </code></pre>
  
  <p>I suspect this tells you a lot. However, I have tried running the command as:</p>
  
  <pre><code>melt input.mp4 -consumer avformat:/output/output.mp4 acodec=libmp3lame
  </code></pre>
  
  <p>... when I do, I do not get the error, but there is still no audio in the output file.</p>
  
  <p>Because I don't really understand audio processing, I'm not sure if I'm missing plugins or somehow otherwise not specifying a requirement. Should be a relatively easy fix for someone who knows their way around Docker and multimedia.</p>