This issue is almost 6 months old and still unanswered. This
should be a very easy question for you to answer. In fact, you
should have a compatibility chart somewhere on your site which
lists this information for much more than just iOS, but all
platforms/browsers/OSes you support. The only place you come close
to this is when you state 'Enter the URL of an Ogg, WebM, flv, mp4,
Youtube, Vimeo or Dailymotion video' on your http://www.universalsubtitles.org/en/videos/create/
page. This is not yet a very developer-friendly website.