[GStreamer] Block legacy VAAPI plugin

https://bugs.webkit.org/show_bug.cgi?id=240664

Patch by Philippe Normand <philn@igalia.com> on 2022-05-20
Reviewed by Xabier Rodriguez-Calvar.

The VAAPI plugin is not much maintained anymore and prone to rendering issues. In the
mid-term we will leverage the new stateless VA decoders. Disable the legacy plugin,
unless the WEBKIT_GST_ENABLE_LEGACY_VAAPI environment variable is set to 1.

* Source/WebCore/platform/graphics/gstreamer/GStreamerCommon.cpp:
(WebCore::registerWebKitGStreamerElements):

Canonical link: https://commits.webkit.org/250795@main
git-svn-id: https://svn.webkit.org/repository/webkit/trunk@294540 268f45cc-cd09-0410-ab3c-d52691b4dbfc

Source/WebCore/platform/graphics/gstreamer/GStreamerCommon.cpp

@@ -383,6 +383,16 @@ void registerWebKitGStreamerElements()
                     gst_plugin_feature_set_rank(GST_PLUGIN_FEATURE_CAST(factory.get()), GST_RANK_NONE);
             }
         }
+
+        // The VAAPI plugin is not much maintained anymore and prone to rendering issues. In the
+        // mid-term we will leverage the new stateless VA decoders. Disable the legacy plugin,
+        // unless the WEBKIT_GST_ENABLE_LEGACY_VAAPI environment variable is set to 1.
+        const char* enableLegacyVAAPIPlugin = getenv("WEBKIT_GST_ENABLE_LEGACY_VAAPI");
+        if (!enableLegacyVAAPIPlugin || !strcmp(enableLegacyVAAPIPlugin, "0")) {
+            auto* registry = gst_registry_get();
+            if (auto vaapiPlugin = adoptGRef(gst_registry_find_plugin(registry, "vaapi")))
+                gst_registry_remove_plugin(registry, vaapiPlugin.get());
+        }
     });
 }