I don't think old requests are properly cleaned up when changing sources, i.e. I can see in the Chrome Dev Tools that they continue downloading...

In _updateSource, instead of just doing:

// Remove the old media
_remove(plyr.media);

I think the following is required:

plyr.media.pause();
plyr.media.src = '';
plyr.media.load();
// Remove the old media
_remove(plyr.media);