diff --git a/lib/upipe-modules/upipe_aggregate.c b/lib/upipe-modules/upipe_aggregate.c
index 696e8395e..525e02eb0 100644
--- a/lib/upipe-modules/upipe_aggregate.c
+++ b/lib/upipe-modules/upipe_aggregate.c
@@ -1,5 +1,6 @@
 /*
  * Copyright (C) 2013-2015 OpenHeadend S.A.R.L.
+ * Copyright (C) 2024 EasyTools
  *
  * Authors: Benjamin Cohen
  *
@@ -111,6 +112,61 @@ static struct upipe *upipe_agg_alloc(struct upipe_mgr *mgr,
     return upipe;
 }
 
+/** @internal @This flushes the aggregated buffer.
+ *
+ * @param upipe description structure of the pipe
+ * @param upump_p reference to pump that generated the buffer
+ */
+static void upipe_agg_flush(struct upipe *upipe, struct upump **upump_p)
+{
+    struct upipe_agg *upipe_agg = upipe_agg_from_upipe(upipe);
+    struct uref *uref = upipe_agg->aggregated;
+    upipe_agg->aggregated = NULL;
+    if (uref)
+        upipe_agg_output(upipe, uref, upump_p);
+}
+
+/** @internal @This sets the input flow definition for real.
+ *
+ * @param upipe description structure of the pipe
+ * @param flow_def flow definition packet
+ * @return an error code
+ */
+static int upipe_agg_set_flow_def_real(struct upipe *upipe,
+                                       struct uref *flow_def)
+{
+    struct upipe_agg *upipe_agg = upipe_agg_from_upipe(upipe);
+    uint64_t size = 0;
+    uint64_t octetrate = 0;
+    uint64_t latency = 0;
+
+    uref_block_flow_get_size(flow_def, &size);
+    uref_block_flow_get_octetrate(flow_def, &octetrate);
+    uref_clock_get_latency(flow_def, &latency);
+
+    upipe_agg->input_size = size;
+
+    int err = uref_block_flow_set_size(flow_def, upipe_agg->output_size);
+    if (unlikely(!ubase_check(err))) {
+        uref_free(flow_def);
+        upipe_throw_fatal(upipe, err);
+        return err;
+    }
+
+    if (octetrate) {
+        latency += (uint64_t)upipe_agg->output_size * UCLOCK_FREQ / octetrate;
+        err = uref_clock_set_latency(flow_def, latency);
+        if (unlikely(!ubase_check(err))) {
+            uref_free(flow_def);
+            upipe_throw_fatal(upipe, err);
+            return err;
+        }
+    }
+    upipe_agg_store_flow_def(upipe, flow_def);
+    return UBASE_ERR_NONE;
+}
+
+
 /** @internal @This receives data.
  *
  * @param upipe description structure of the pipe
@@ -124,6 +180,12 @@ static void upipe_agg_input(struct upipe *upipe, struct uref *uref,
     size_t size = 0;
     const size_t output_size = upipe_agg->output_size;
 
+    if (unlikely(ubase_check(uref_flow_get_def(uref, NULL)))) {
+        upipe_agg_flush(upipe, upump_p);
+        upipe_agg_set_flow_def_real(upipe, uref);
+        return;
+    }
+
     uref_block_size(uref, &size);
 
     /* check for invalid or too large size */
@@ -135,10 +197,8 @@ static void upipe_agg_input(struct upipe *upipe, struct uref *uref,
     }
 
     /* flush if incoming packet makes aggregated overflow */
-    if (upipe_agg->size + size > output_size) {
-        upipe_agg_output(upipe, upipe_agg->aggregated, upump_p);
-        upipe_agg->aggregated = NULL;
-    }
+    if (upipe_agg->size + size > output_size)
+        upipe_agg_flush(upipe, upump_p);
 
     /* keep or attach incoming packet */
     if (unlikely(!upipe_agg->aggregated)) {
@@ -159,11 +219,8 @@ static void upipe_agg_input(struct upipe *upipe, struct uref *uref,
     /* anticipate next packet size and flush now if necessary */
     if (upipe_agg->input_size)
         size = upipe_agg->input_size;
-    if (unlikely(upipe_agg->size + size > output_size)) {
-        upipe_agg_output(upipe, upipe_agg->aggregated, upump_p);
-        upipe_agg->aggregated = NULL;
-        upipe_agg->size = 0;
-    }
+    if (unlikely(upipe_agg->size + size > output_size))
+        upipe_agg_flush(upipe, upump_p);
 }
 
 /** @internal @This sets the input flow definition.
@@ -178,26 +235,10 @@ static int upipe_agg_set_flow_def(struct upipe *upipe, struct uref *flow_def)
         return UBASE_ERR_INVALID;
     UBASE_RETURN(uref_flow_match_def(flow_def, EXPECTED_FLOW_DEF))
 
-    struct upipe_agg *upipe_agg = upipe_agg_from_upipe(upipe);
-    uint64_t size = 0;
-    uref_block_flow_get_size(flow_def, &size);
-    upipe_agg->input_size = size;
-
-    uint64_t octetrate = 0;
-    uref_block_flow_get_octetrate(flow_def, &octetrate);
-    uint64_t latency = 0;
-    uref_clock_get_latency(flow_def, &latency);
-
     struct uref *flow_def_dup;
     if ((flow_def_dup = uref_dup(flow_def)) == NULL)
         return UBASE_ERR_ALLOC;
-    UBASE_RETURN(uref_block_flow_set_size(flow_def_dup, upipe_agg->output_size))
-
-    if (octetrate) {
-        UBASE_RETURN(uref_clock_set_latency(flow_def_dup, latency +
-                    (uint64_t)upipe_agg->output_size * UCLOCK_FREQ / octetrate))
-    }
-    upipe_agg_store_flow_def(upipe, flow_def_dup);
+    upipe_agg_input(upipe, flow_def_dup, NULL);
     return UBASE_ERR_NONE;
 }