Brightcove videos info is usually found in an <object class="BrightcoveExperience"></object> node, this is passed to a new method of BrightcoveIE that builds a url to extract the video.
When a IE is added to the list, it's also added to a dictionary. When a IE is requested it first looks in the dictionary and if there's no instance it will create a new one.
That way _real_initialize is only called once for each IE, saving time if it needs to login for example.