I want to save a meta data to post parent when the media-form on gallery tab is saved( The submission button is “Save All Changes”). Which action hook can I use?
For updates it is
'edit_attachment' and for new attachments
There is no action dedicated to images coming from the gallery tab, but you could check the global array
$_FILES. If there is a
$_FILES['async-upload'] it is probably a request from the media popup.