title: Cannot join mp3 file and avi file with ffmpeg
body: <p>I am using this code to join an mp3 file and video file with ffmpeg</p>
  
  <pre><code>ffmpeg -i /file1.mp3 -ab 128k -i /file2.avi  -vcodec copy -f avi /file3.avi
  </code></pre>
  
  <p>But this code gives that error</p>
  
  <pre><code>Option ab (audio bitrate (please use -b:a)) cannot be applied to input file /file1.mp3 -- you are trying to apply an input option to an output file or vice versa. Move this option before the file it belongs to.
  Error parsing options for input file /file1.mp3.
  Error opening input files: Invalid argument
  </code></pre>
  
  <p>How can i do this job ?</p>