title: Combining an audio file with a video file
body: <p>I have two files: one audio and one video (mp4).</p>
  
  <p>I want to create from those two files, one video file that will contain both the audio and video output. The main issue is the synchronization between both of those recorded files. There's a man speaking, and the movement and sound need to line up.</p>
  
  <p>I heard about the FFmpeg library for iOS but didn't found any good information about it.</p>