Currently the WebM handling seems to assume there will be a video stream; however .webm files may be audio-only as well (in which case it's a Vorbis, or potentially maybe Opus audio track with no video).

Currently I can upload such a file, but I get some bad behavior as a result.

Compare audio-only .webm:

http://ogvjs-testing.wmflabs.org/wiki/File:Bach.webm

versus audio-only .ogg:

http://ogvjs-testing.wmflabs.org/wiki/File:Bach_-_Brandenburg_Concerto_No._3_-_1._Allegro.ogg

• Nasty warnings visible during display of the file page, and parsing of a page that embeds:
  
  Notice: Undefined index: video in /srv/vagrant/mediawiki/extensions/TimedMediaHandler/handlers/WebMHandler/WebMHandler.php on line <i>123</i>

• File page's info marks it as 'audio/video file' and gives empty dimensions where it should be 'audio file' with no dimensions
  
  "(WebM audio/video file, Vorbis, length 5 min 19 s, 0 × 0 pixels, 256 kbps overall)"

• Embedded player is marked as video, has a tiny audio icon thumbnail, and seems to be not initialized properly

• Media type returned from API is 'VIDEO', not 'AUDIO':

http://ogvjs-testing.wmflabs.org/w/api.php?format=jsonfm&action=query&titles=File:Bach.webm&prop=imageinfo&iiprop=mediatype

• No .ogg transcode is made (not sure if that's really necessary; I can extend ogv.js to support webm containers for the browsers that don't do WebM natively)

Version: unspecified
Severity: normal
URL: http://ogvjs-testing.wmflabs.org/wiki/File:Bach.webm