es_out: add auto es selection policy

No real way to handle declared alternate video streams
such as with live stream.

Refactors selection stuff and leaves room
for more improvement.

Policy change does not alter previous es selection.
Demuxers must make changes then before creating es.

include/vlc_es_out.h

@@ -46,6 +46,9 @@ enum es_out_query_e
     ES_OUT_SET_ES_STATE,/* arg1= es_out_id_t* arg2=bool   */
     ES_OUT_GET_ES_STATE,/* arg1= es_out_id_t* arg2=bool*  */
 
+    /* sets es selection policy when in auto mode */
+    ES_OUT_SET_ES_CAT_POLICY, /* arg1=es_format_category_e arg2=es_out_policy_e */
+
     /* */
     ES_OUT_SET_GROUP,   /* arg1= int                            */
 
@@ -92,6 +95,12 @@ enum es_out_query_e
     ES_OUT_PRIVATE_START = 0x10000,
 };
 
+enum es_out_policy_e
+{
+    ES_OUT_ES_POLICY_EXCLUSIVE = 0,/* Enforces single ES selection only */
+    ES_OUT_ES_POLICY_SIMULTANEOUS, /* Allows multiple ES per cat */
+};
+
 struct es_out_t
 {
     es_out_id_t *(*pf_add)    ( es_out_t *, const es_format_t * );