It seems that Score does not work well with the VideoJS player. When the TimedMediaHandler extension is enabled and there is another media element on a page, TMH tries to apply VideoJS to Score elements that have sound="1"
but results in a disabled player with sound source File:Undefined. See phabricator:T245377. For the time being I'm forcing the Kaltura player which plays nicely in all circumstances ($wgTmhWebPlayer = "mwembed";
).
Topic on Extension talk:Score
phab:T306836 and phab:T306836 have been fixed, and I think with phab:T248418 VideoJS is now the default player on all wikis.