options: hide encoding AO/VO in help output

These can't be used manually. Encoding is enabled with -o instead, and
the encoding AO/VO is selected using internal mechanisms.

audio/out/ao.c

@@ -107,6 +107,7 @@ static bool get_desc(struct m_obj_desc *dst, int index)
         .priv_size = ao->priv_size,
         .priv_defaults = ao->priv_defaults,
         .options = ao->options,
+        .hidden = ao->encode,
         .p = ao,
     };
     return true;

core/m_option.c

@@ -2283,8 +2283,10 @@ static int parse_obj_settings_list(const m_option_t *opt, struct bstr name,
             struct m_obj_desc desc;
             if (!ol->get_desc(&desc, n))
                 break;
-            mp_msg(MSGT_CFGPARSER, MSGL_INFO, "  %-15s: %s\n",
-                   desc.name, desc.description);
+            if (!desc.hidden) {
+                mp_msg(MSGT_CFGPARSER, MSGL_INFO, "  %-15s: %s\n",
+                       desc.name, desc.description);
+            }
         }
         mp_msg(MSGT_CFGPARSER, MSGL_INFO, "\n");
         return M_OPT_EXIT - 1;

core/m_option.h

@@ -110,6 +110,8 @@ struct m_obj_desc {
     // This member is usually set my m_obj_list_find() only.
     // Only works if options is not NULL.
     const char *init_options;
+    // Don't list entries with "help"
+    bool hidden;
 };
 
 // Extra definition needed for \ref m_option_type_obj_settings_list options.

video/out/vo.c

@@ -115,6 +115,7 @@ static bool get_desc(struct m_obj_desc *dst, int index)
         .priv_defaults = vo->priv_defaults,
         .options = vo->options,
         .init_options = vo->init_option_string,
+        .hidden = vo->encode,
         .p = vo,
     };
     return true;