In WP 3.4.x and earlier, it was possible to add a button to the media manager by messing around in an
attachment_fields_to_edit filter. For example, a plugin could, when it figured out that an item was an audio file, append some HTML for an extra button to the url field, like so.
$playertag = "[audio $url]"; $fields['url']['html'] .= "<button type='button' class='button data-link-url='$playertag' urlaudioplayer audio-player-$postid'>Audio Player</button>";
The new media manager has changed the set of buttons that were in that html tag into a pulldown menu -- a
<select .../> item. The html code is emitted in media-template.php. The new code still calls
attachment_fields_to_edit filters, but doesn't pass in any fields.
Is there a way to extend this select item without hacking the core (which I won't do). Is it conceivable to write a bit of js which will use jQuery to add an item to it?