edit

lib/Store/Core.php

@@ -668,6 +668,7 @@ class Core
 			'application/vnd.android.package-archive' => 'apk',
 			'audio/webm' => 'webm',
 			'video/webm' => 'webm',
+			'audio/x-m4a' => 'm4a',
 		);
 
 		if (isset($config[$mine])) {