title: FFmpeg using complex filter amerge doesn't play on iOS
body: <p>I am using 2 different FFmpeg commands to add audio to a video:
  This adds audio and replace video's existing audio: </p>
  
  <p>ffmpeg -i "inputVideo.wmv" -i "inputAudio.mp3" -map 0:v -map 1:a -shortest -vcodec libx264 -preset ultrafast -crf 22 -pix_fmt yuv420p -r 30 "outputVideo.mp4"</p>
  
  <p>It works fine.</p>
  
  <p>The problem comes when I try to mix the new audio with the video's existing audio:</p>
  
  <p>ffmpeg -i "inputVideo.wmv" -i "inputAudio.mp3" -filter_complex "[0:a][1:a]amerge=inputs=2[a]" -map 0:v -map "[a]" -shortest -vcodec libx264 -preset ultrafast -crf 22 -pix_fmt yuv420p -r 30 "outputVideo.mp4"</p>
  
  <p>The video plays fine everywhere but on iOS.  I've tried adding -profile:v main -level 3.1  and -profile:v baseline -level 3.1 but no luck either.</p>
  
  <p>ffmpeg -i "inputVideo.wmv" -i "inputAudio.mp3" -filter_complex "[0:a][1:a]amerge=inputs=2[a]" -map 0:v -map "[a]" -shortest -vcodec libx264 -profile:v baseline -level 3.1 -preset ultrafast -crf 22 -pix_fmt yuv420p -r 30 "outputVideo.mp4"</p>
  
  <p>WHat do I need to do to make the output video play on iOS?</p>