WebM transcodes created with the configuration in MediaWiki-Vagrant and Labs-Vagrant are much lower quality, and at a lower total bitrate, than expected.
Example... This Ogg transcode is correct bitrate:
while its WebM sibling is much lower bitrate and visibly much poorer quality:
Disabling the "'twopass' => true" setting in the transcode options in WebVideoTranscode.php fixes it for me, but it seems like this should work with two-pass encoding, especially as I assume that's what's being used in production...