Value from ajaxified form field not passed to ajax callback
$form_state['values']['field_video_reference']['und'][0]['target_id'] looks wrong to me.

I would expect the value to be in $form_state['values']['field_video_reference'].

If you haven't already then install the Devel module and then use can use dpm($form_state); to output the array to the message area and inspect it to find the correct path.

Sometimes for ajax requests Devel Debug Log is also useful as it allows you to send a dump of a variable to a log so you can inspect it even if it is not possible to send content to the message area.