upipe_avfilter: factorize main and sub pipe code

Author: quarium

include/upipe-av/uref_avfilter_flow.h

@@ -36,8 +36,31 @@ extern "C" {
 
 #include "upipe/uref_attr.h"
 
+/** @This define the void flow def prefix. */
+#define UREF_AVFILT_FLOW_DEF  "avfilt."
+
 UREF_ATTR_STRING(avfilt_flow, name, "avfilt.name", avfilter name)
 
+/** @This allocates a new avfilt flow.
+ *
+ * @param mgr uref management structure
+ * @return pointer to uref void flow
+ */
+static inline struct uref *uref_avfilt_flow_alloc_def(struct uref_mgr *mgr,
+                                                      const char *name)
+{
+    struct uref *uref = uref_alloc_control(mgr);
+    if (unlikely(!uref))
+        return NULL;
+
+    if (unlikely(!ubase_check(uref_flow_set_def(uref, UREF_AVFILT_FLOW_DEF)) ||
+                 !ubase_check(uref_avfilt_flow_set_name(uref, name)))) {
+        uref_free(uref);
+        return NULL;
+    }
+    return uref;
+}
+
 #ifdef __cplusplus
 }
 #endif