From 892bea99cdbcd47a7c61528e04dda67413b61cae Mon Sep 17 00:00:00 2001
From: Philippe Normand <philn@igalia.com>
Date: Tue, 15 Oct 2024 15:58:53 +0100
Subject: [PATCH] encodebasebin: Fix parser selection

If an encoder supports multiple codecs (a bin wrapping/auto-plugging encoders)
then its src pad template caps might list the supported codecs. Without this
patch the selected parser would be the one corresponding to the first codec,
leading to caps negotiation error later on. The proposed fix is to check the
media type on the parser candidates sink pad templates according to the
requested encoded format.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/7756>
---
 .../gst/encoding/gstencodebasebin.c           | 52 +++++++++++++++----
 1 file changed, 42 insertions(+), 10 deletions(-)

diff --git a/subprojects/gst-plugins-base/gst/encoding/gstencodebasebin.c b/subprojects/gst-plugins-base/gst/encoding/gstencodebasebin.c
index 1d64d4d34c..488a26dd17 100644
--- a/subprojects/gst-plugins-base/gst/encoding/gstencodebasebin.c
+++ b/subprojects/gst-plugins-base/gst/encoding/gstencodebasebin.c
@@ -831,8 +831,18 @@ _create_compatible_processor (GList * all_processors,
 {
   GList *processors1, *processors, *tmp;
   GstElement *processor = NULL;
-  GstElementFactory *factory = NULL;
   GstCaps *format = NULL;
+  GstCaps *encoding_format = NULL;
+  GstStructure *s;
+  const gchar *encoding_media_type;
+
+  encoding_format = gst_encoding_profile_get_format (sprof);
+  if (G_UNLIKELY (gst_caps_is_empty (encoding_format))) {
+    return NULL;
+  }
+
+  s = gst_caps_get_structure (encoding_format, 0);
+  encoding_media_type = gst_structure_get_name (s);
 
   if (encoder) {
     GstPadTemplate *template = gst_element_get_pad_template (encoder, "src");
@@ -843,7 +853,7 @@ _create_compatible_processor (GList * all_processors,
 
   if (!format || gst_caps_is_any (format)) {
     gst_clear_caps (&format);
-    format = gst_encoding_profile_get_format (sprof);
+    format = gst_caps_ref (encoding_format);
   }
 
   GST_DEBUG ("Getting list of processors for format %" GST_PTR_FORMAT, format);
@@ -864,20 +874,42 @@ _create_compatible_processor (GList * all_processors,
   }
 
   for (tmp = processors; tmp; tmp = tmp->next) {
-    /* FIXME : We're only picking the first one so far */
-    /* FIXME : signal the user if he wants this */
-    factory = (GstElementFactory *) tmp->data;
+    GstElementFactory *candidate_factory = GST_ELEMENT_FACTORY_CAST (tmp->data);
+    GstPadTemplate *tmpl;
+    GstCaps *processor_caps;
+    gboolean is_compatible = FALSE;
+
+    processor = gst_element_factory_create (candidate_factory, NULL);
+    tmpl = gst_element_get_pad_template (processor, "sink");
+    processor_caps = gst_pad_template_get_caps (tmpl);
+
+    if (gst_caps_is_any (processor_caps)) {
+      is_compatible = TRUE;
+    } else if (!gst_caps_is_empty (processor_caps)) {
+      GstStructure *structure = gst_caps_get_structure (processor_caps, 0);
+      if (!strcmp (encoding_media_type, gst_structure_get_name (structure))) {
+        is_compatible = TRUE;
+      }
+    }
+
+    gst_clear_caps (&processor_caps);
+
+    if (!is_compatible) {
+      GST_DEBUG ("Processor %" GST_PTR_FORMAT " is not compatible with format %"
+          GST_PTR_FORMAT, processor, encoding_format);
+      gst_clear_object (&processor);
+      continue;
+    }
+
+    /* FIXME : signal the user if he wants this parser */
     break;
   }
 
-  if (factory)
-    processor = gst_element_factory_create (factory, NULL);
-
   gst_plugin_feature_list_free (processors);
 
 beach:
-  if (format)
-    gst_caps_unref (format);
+  gst_clear_caps (&format);
+  gst_clear_caps (&encoding_format);
 
   return processor;
 }