title: node.js : fluent-ffmpeg throws error when converting mp4 to mp3
body: <p>I'm trying to convert an mp4 video to mp3 with node's fluent-ffmpeg module. Here is my code:</p>
  
  <pre><code>ffmpeg = require 'fluent-ffmpeg'
  
  mp4 = '/Users/jashua/Desktop/video.mp4'
  mp3 = '/Users/jashua/Desktop/audio.mp3'
  
  proc = new ffmpeg({source:mp4})
      .toFormat('mp3')
      .setFfMpegPath('/Applications/ffmpeg')
      .saveToFile(mp3, (stdout, stderr)-&gt;
              return console.log stderr if err?
              return console.log 'done'
          )
  </code></pre>
  
  <p>On running it, I get the following error:</p>
  
  <pre><code>TypeError: Cannot call method 'saveToFile' of undefined
  at Object.&lt;anonymous&gt; (/Users/jashua/Desktop/ytdl.coffee:10:12, &lt;js&gt;:18:60)
    at Object.&lt;anonymous&gt; (/Users/jashua/Desktop/ytdl.coffee:1:1, &lt;js&gt;:25:4)
    at Module._compile (module.js:456:26)
  </code></pre>
  
  <p>Any ideas?</p>
  
  <p>Solution: </p>
  
  <pre><code>proc = new ffmpeg({source:mp4})
      proc.setFfMpegPath('/Applications/ffmpeg')
      proc.saveToFile(mp3, (stdout, stderr)-&gt;
                  return console.log stderr if err?
                  return console.log 'done'
              )
      enter code here
  </code></pre>