I want to support the upload of a new standardized audio format (AMR), and after some initial looking around, noticed that functions.php contains a function called wp_check_filetype that seems to validate the type based on the file extension. So great, I thought; I just need to add "'amr' => 'audio/amr'" to the list, and that should fix it. Only that still doesn't work - I continue to get the "security" alert when I try to upload it, despite the file name having the amr extension.
There must be something obvious I'm missing. Any idea what it might be?