There is a bug with the cloak url function when using mp3 on Safari on Mac and IOS.

Safari can play audio/video that is cloaked using download.php but it loads it as a playlist file (m3u8) despite the MIME type being set as mpeg audio. The result is that the mp3 is not seekable and video metadata cannot be extracted. ... ekable-php

I think that couch/download.php needs to implement some of the suggestions in the link above