From c1ec23a75e81a7f1e4ca36e37074991b71516b85 Mon Sep 17 00:00:00 2001
From: Edward Hervey <edward@centricular.com>
Date: Mon, 10 Jun 2024 14:56:00 +0200
Subject: [PATCH] decodebin3: Always ensure we end up with parsebin or identity

This fixes a regression introduced by 6c4f52ea20ce27730501348c6e575b8d35580239

There are cases where the input stream will be push-based, time-segment and not
have a collection nor caps. This means the event-based checks are not sufficient
to decide when/where to plug in a identity or parsebin to process the input.

For those corner cases we setup a buffer probe to ensure we always end up with
at least a parsebin

Fixes #3609

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/7018>
---
 .../gst/playback/gstdecodebin3.c              | 46 +++++++++++++++++++
 1 file changed, 46 insertions(+)

diff --git a/subprojects/gst-plugins-base/gst/playback/gstdecodebin3.c b/subprojects/gst-plugins-base/gst/playback/gstdecodebin3.c
index be27a6cc45..9cc2f9f9d1 100644
--- a/subprojects/gst-plugins-base/gst/playback/gstdecodebin3.c
+++ b/subprojects/gst-plugins-base/gst/playback/gstdecodebin3.c
@@ -376,6 +376,9 @@ struct _DecodebinInput
   /* List of events that need to be pushed once we get the first
    * GST_EVENT_STREAM_COLLECTION */
   GList *events_waiting_for_collection;
+
+  /* input buffer probe for detecting whether input has caps or not */
+  gulong input_probe;
 };
 
 /* Streams that come from parsebin or identity */
@@ -1627,6 +1630,23 @@ no_parsebin:
   }
 }
 
+static GstPadProbeReturn
+input_pad_buffer_probe (GstPad * pad, GstPadProbeInfo * info,
+    gpointer user_data)
+{
+  DecodebinInput *input = user_data;
+
+  INPUT_LOCK (input->dbin);
+  if (!input->parsebin && !input->identity) {
+    GST_DEBUG_OBJECT (pad, "Push-stream without caps, setting up identity");
+    gst_decodebin_input_ensure_parsebin (input);
+  }
+  input->input_probe = 0;
+  INPUT_UNLOCK (input->dbin);
+
+  return GST_PAD_PROBE_REMOVE;
+};
+
 static GstPadLinkReturn
 gst_decodebin3_input_pad_link (GstPad * pad, GstObject * parent, GstPad * peer)
 {
@@ -1662,6 +1682,15 @@ gst_decodebin3_input_pad_link (GstPad * pad, GstObject * parent, GstPad * peer)
           "Can't reconfigure input from push-based to pull-based");
       res = GST_PAD_LINK_REFUSED;
     }
+  } else if (input->input_probe == 0) {
+    /* We setup a buffer probe to handle the corner case of push-based
+     * time-based inputs without CAPS/COLLECTION. If we get a buffer without
+     * having figured out if we need identity or parsebin, we will plug in
+     * parsebin */
+    GST_DEBUG_OBJECT (pad, "Setting up buffer probe");
+    input->input_probe =
+        gst_pad_add_probe (pad, GST_PAD_PROBE_TYPE_BUFFER,
+        input_pad_buffer_probe, input, NULL);
   }
 
   /* Clear stream-collection corresponding to current INPUT.  We do not
@@ -1880,6 +1909,11 @@ gst_decodebin_input_reset (DecodebinInput * input)
   if (input->collection)
     gst_clear_object (&input->collection);
 
+  if (input->input_probe) {
+    gst_pad_remove_probe (input->ghost_sink, input->input_probe);
+    input->input_probe = 0;
+  }
+
   g_list_free_full (input->events_waiting_for_collection,
       (GDestroyNotify) gst_event_unref);
   input->events_waiting_for_collection = NULL;
@@ -2090,6 +2124,12 @@ sink_event_function (GstPad * sinkpad, GstDecodebin3 * dbin, GstEvent * event)
       if (!input->parsebin && !input->identity)
         gst_decodebin_input_setup_identity (input);
 
+      /* Remove buffer probe for caps/collection detection */
+      if (input->input_probe) {
+        gst_pad_remove_probe (sinkpad, input->input_probe);
+        input->input_probe = 0;
+      }
+
       /* Drain all pending events */
       if (input->events_waiting_for_collection) {
         GList *tmp;
@@ -2109,6 +2149,12 @@ sink_event_function (GstPad * sinkpad, GstDecodebin3 * dbin, GstEvent * event)
         break;
       GST_DEBUG_OBJECT (sinkpad, "new caps %" GST_PTR_FORMAT, newcaps);
 
+      /* Remove buffer probe for caps/collection detection */
+      if (input->input_probe) {
+        gst_pad_remove_probe (sinkpad, input->input_probe);
+        input->input_probe = 0;
+      }
+
       /* No parsebin or identity present, check if we can avoid creating one */
       if (!input->parsebin && !input->identity) {
         if (gst_decodebin_input_requires_parsebin (input, newcaps)) {