I am experiencing a 100% reproducible error playing a .webm video, with Safari 10.1.1 on Mac OS 10.12.5. Because my browser does not support wemb it uses the Javascript media player, and it is that that is failing.
The video is https://commons.wikimedia.org/wiki/File:Editing_basics_-_Uploading_and_adding_images.webm. Whether I play it on the page it was first noticed, https://en.wikipedia.org/wiki/Wikipedia:Tutorial/Editing, or its page on en.wp or commons, I see the same problem, a spinning white 'loading' icon, no video, and an error in the browser’s console:
[Error] TypeError: undefined is not an object (evaluating 'mimeType.split')
getMIMETypePlayers (mw.MediaPlayers.js:95)
defaultPlayer (mw.MediaPlayers.js:118)
isPlayableType (mw.MediaElement.js:430)
getPlayableSources (mw.MediaElement.js:476)
autoSelectSource (mw.MediaElement.js:165)
setupSourcePlayer (mw.EmbedPlayer.js:688)
(anonymous function) (mw.EmbedPlayer.js:615)
doCallbackCheck (load.php:329)
(anonymous function) (mw.MediaWikiPlayerSupport.js:334)
(anonymous function) (load.php:337)
each (load.php:384)
triggerQueueCallback (load.php:336)
checkPlayerSources (mw.EmbedPlayer.js:614)
(anonymous function) (mw.processEmbedPlayers.js:115)
triggerQueueCallback (load.php:307)
runPlayerSwap (mw.processEmbedPlayers.js:112)
addPlayerElement (mw.processEmbedPlayers.js:131)
(anonymous function) (mw.processEmbedPlayers.js:343)
each (load.php:384)
each (load.php:136)
processEmbedPlayers (mw.processEmbedPlayers.js:335)
(anonymous function) (jquery.embedPlayer.js:43)
It only seems to be with this video: other .webm videos I have tried on commons worked fine. If I download the video and play it in VLC it plays fine too.