Accessibility/HTML5 captions v3

<video>
<source src="video.ogv" type="video/ogg">
<tracks>
 <track id='ogg_v' role='video' ref='serialno:1505760010'></track>
 <track id='ogg_a' role='audio' lang='en' ref='serialno:0821695999'></track>
 <track id='ogg_ad' role='auddesc' lang='en' ref='serialno:1421614520'></track>
 <track id='ogg_s' role='sign' lang='ase' ref='serialno:1413244634'></track>
 <track id='ogg_cc' role='caption' lang='en' ref='serialno:1421849818'></track>
</tracks>
<source src="video.mp4" type="video/mp4">
<tracks>
 <track id='mp4_v' role='video' ref='trackid:1'></track>
 <track id='mp4_a' role='audio' lang='en' ref='trackid:2'></track>
</tracks>
<textassoc role="caption" style="font-size:2em;padding:1em;text-align:center;display: block;">
  <source src="en-us.srt" lang="en-US">
  <source src="en.srt" lang="en">
  <source ref='serialno:1421849818' lang="en">
</textassoc>
<textassoc role="tad" style="z-index: -100; display: block;" aria-live="assertive">
  <source src="tad-en.srt" lang="en">
  <source src="tad-de.srt" lang="de">
</textassoc>
<textassoc role="subtitle" style="font-size:2em;padding:1em;text-align:center; display: block;">
  <source src="de.srt" lang="de">
  <source src="sv.srt" lang="sv">
  <source src="fi.srt" lang="fi">
</textassoc>
</video>