Upstream ticket: https://secure.phabricator.com/T6916 (merged from https://secure.phabricator.com/T6674 )
The screencast on T62541#649353 (from https://old-bugzilla.wikimedia.org/show_bug.cgi?id=60541#c1) doesn't work for me on Firefox or Chrome.
The source code shows it is an <audio> tag, but since the attachment is a screencast (containing only video), this doesn't look right.