From 93e432bccb09e480059039df62695adeb71e3787 Mon Sep 17 00:00:00 2001
From: Edward Hervey <edward@centricular.com>
Date: Mon, 25 Nov 2024 10:50:34 +0100
Subject: [PATCH] urisourcebin: Fix issue re-using outputs

When checking whether a no-longer used output could be re-used for another slot,
we only want to do that for streams which are not still used.

Otherwise we end up potentially re-assigning a demuxer stream to a completely
different one

Furthermore, if we *are* re-using an output slot, indicate what the replacement
GstStream will be so slot matching can work properly (which can happen in the
case of demuxers which add/remove all pads even if only a single one changed)

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/7949>
---
 .../gst/playback/gsturisourcebin.c            | 36 +++++++++++++++----
 1 file changed, 29 insertions(+), 7 deletions(-)

diff --git a/subprojects/gst-plugins-base/gst/playback/gsturisourcebin.c b/subprojects/gst-plugins-base/gst/playback/gsturisourcebin.c
index 7e1b9910a0..b1978c4068 100644
--- a/subprojects/gst-plugins-base/gst/playback/gsturisourcebin.c
+++ b/subprojects/gst-plugins-base/gst/playback/gsturisourcebin.c
@@ -2892,6 +2892,7 @@ handle_parsebin_collection (ChildSrcPadInfo * info,
 {
   GList *unused_slots = NULL, *iter;
   GList *streams = NULL;
+  GList *unused_streams = NULL;
   guint i, nb_streams;
 
   nb_streams = gst_stream_collection_get_size (collection);
@@ -2900,33 +2901,54 @@ handle_parsebin_collection (ChildSrcPadInfo * info,
         g_list_append (streams, gst_stream_collection_get_stream (collection,
             i));
 
+  unused_streams = g_list_copy (streams);
+
   /* Get list of output info slots not present in the collection */
   for (iter = info->outputs; iter; iter = iter->next) {
     OutputSlotInfo *output = iter->data;
 
-    if (output->stream
-        && !gst_playback_utils_stream_in_list (streams, output->stream)) {
+    if (!output->stream)
+      continue;
+
+    if (!gst_playback_utils_stream_in_list (streams, output->stream)) {
       GST_DEBUG_OBJECT (output->originating_pad,
           "No longer used in new collection");
       unused_slots = g_list_append (unused_slots, output);
+    } else {
+      GList *iter2 = unused_streams;
+      /* Stream is re-used, remove it from unused streams we will try to
+       * re-assign further down */
+      for (iter2 = unused_streams; iter2; iter2 = iter2->next) {
+        GstStream *stream = iter2->data;
+        if (!g_strcmp0 (output->stream->stream_id, stream->stream_id)) {
+          /* Replace the pending stream by the incoming stream */
+          gst_object_replace ((GstObject **) & output->pending_stream,
+              (GstObject *) stream);
+          unused_streams = g_list_remove (unused_streams, stream);
+          break;
+        }
+      }
     }
   }
 
-  /* For each of those slots, check if there is a compatible stream from the
-   * collection that could be assigned to it */
+  /* For each of those slots, check if there is a unused compatible stream from
+   * the collection that could be assigned to it */
   for (iter = unused_slots; iter; iter = iter->next) {
     OutputSlotInfo *output = iter->data;
-    GstStream *replacement = find_compatible_stream (streams, output->stream);
+    GstStream *replacement =
+        find_compatible_stream (unused_streams, output->stream);
     if (replacement) {
       GST_DEBUG_OBJECT (output->originating_pad, "Assigning stream %s",
           gst_stream_get_stream_id (replacement));
-      output->pending_stream = gst_object_ref (replacement);
-      streams = g_list_remove (streams, replacement);
+      gst_object_replace ((GstObject **) & output->pending_stream,
+          (GstObject *) replacement);
+      unused_streams = g_list_remove (unused_streams, replacement);
     }
   }
 
   g_list_free (unused_slots);
   g_list_free (streams);
+  g_list_free (unused_streams);
 
   /* Store the collection */
   gst_object_replace ((GstObject **) & info->collection,