title: How can I convert mp4 video file to mp3 in objective c?
body: <p>I 'm recording a video with AVFoundation framework and save this. I want get the audio file of this video because in avfoundation I record all in the same file, but I don't know how to do this and I don't find never ask about this.</p>
  
  <p>I have find a source code that merge video and audio, but not explain hoe to extract this.</p>
  
  <p>how can I do this? I could change mp4 to mov if this is impossible to convert or more easy..</p>
  
  <p>Thanks!</p>