command: add filename/ext property

This will return only the text after the last '.', if any present.
Otherwise, return an empty string.

DOCS/man/input.rst

@@ -1861,12 +1861,16 @@ Property list
     looks better for display purposes. Use the ``path`` property to get an
     unmodified filename.)
 
-    This has a sub-property:
+    This has two sub-properties:
 
     ``filename/no-ext``
         Like the ``filename`` property, but if the text contains a ``.``, strip
         all text after the last ``.``. Usually this removes the file extension.
 
+    ``filename/ext``
+        Returns the text after the final ``.``, if the text contains any.
+        Otherwise, returns an empty string.
+
 ``file-size``
     Length in bytes of the source file/stream. (This is the same as
     ``${stream-end}``. For segmented/multi-part files, this will return the

player/command.c

@@ -464,13 +464,21 @@ static int mp_property_filename(void *ctx, struct m_property *prop,
         f = filename;
     if (action == M_PROPERTY_KEY_ACTION) {
         struct m_property_action_arg *ka = arg;
-        if (strcmp(ka->key, "no-ext") == 0) {
+        bstr key = bstr0(ka->key);
+        if (bstr_equals0(key, "no-ext")) {
             action = ka->action;
             arg = ka->arg;
             bstr root;
             if (mp_splitext(f, &root))
                 f = bstrto0(filename, root);
+        } else if (bstr_equals0(key, "ext")) {
+            action = ka->action;
+            arg = ka->arg;
+            f = mp_splitext(f, NULL);
+            if (!f)
+                f = talloc_strdup(NULL, "");;
         }
+
     }
     int r = m_property_strdup_ro(action, arg, f);
     talloc_free(filename);