title: Unable to use ffprobe in fluent-ffmpeg
body: <p>I was intended to use ffprobe function to extract video information and here is my code:</p>
  
  <pre><code>var FFmpeg = require('fluent-ffmpeg');
  //...
  var convert_using_ffmpeg = function (source, target) {
  
      var tempfile = path.join(config.tmproot, path.basename(target));
  
      new FFmpeg({ source: source })
          .withVideoCodec('libx264')
          .withVideoBitrate('512')
          .withAudioQuality(5)
          .withAudioCodec('libmp3lame')
          .withSize('360x288')
          //.ffprobe(function(err,data) {
          //  console.dir(data);
          //})
          .toFormat('flv')
          .on('error', function (err) {
              console.log('An error occurred: ' + err.message);
          })
          .saveToFile(tempfile, function () {
              fs.rename(tempfile, target);
          });
  };
  </code></pre>
  
  <p>The compiler simply said <code>Object #&lt;FfmpegCommand&gt; has no method 'ffprobe</code> when I execute the program. The fluent-ffmpeg API says I should add FFMPEG_PATH and FFPROBE_PATH environment variable before executing, but the fact is I could execute ffmpeg directly in command line even if it does not exist in PATH environment variable, and the node.js program runs successfully without evoking the ffprobe function. Plus the API also says ffprobe comes together with most distribution of ffmpeg, if so, how can I add ffprobe to the environment variable separately?</p>
  
  <p>I'm using fluent-ffmpeg 1.7.0 currently.</p>