Some mediaselectors may be parseable but have no formats (eg captions only), eg https://www.bbc.co.uk/iplayer/episode/b0b3px4q.
This revision tries all possible mediaselectors and assembles the formats and subtitles found.
If any formats are found, the known exceptions ('notukerror', 'geolocation', 'selectionunavailable') are not propagated.