REGRESSION(r249428): [GStreamer] VP9 video rendered green

https://bugs.webkit.org/show_bug.cgi?id=201422
<rdar://problem/55945741>

Patch by Philippe Normand <philn@igalia.com> on 2019-11-06
Reviewed by Carlos Garcia Campos.

Enable the texture upload GStreamer meta code path. Until
GStreamer 1.16.2 this workaround is needed to fix VP9 (vp9dec)
rendering. For downstream users cherry-picking the corresponding
GStreamer patch[0], an environment variable can be set to bypass
the reintroduced slow color conversion: $WEBKIT_GST_NO_RGBA_CONVERSION.

[0] https://gitlab.freedesktop.org/gstreamer/gst-plugins-base/commit/8d32de090554cf29fe359f83aa46000ba658a693

* platform/graphics/gstreamer/MediaPlayerPrivateGStreamerBase.cpp:
(WebCore::MediaPlayerPrivateGStreamerBase::createVideoSinkGL):

Canonical link: https://commits.webkit.org/217243@main
git-svn-id: https://svn.webkit.org/repository/webkit/trunk@252134 268f45cc-cd09-0410-ab3c-d52691b4dbfc

Source/WebCore/ChangeLog

@@ -1,3 +1,22 @@
+2019-11-06  Philippe Normand  <philn@igalia.com>
+
+        REGRESSION(r249428): [GStreamer] VP9 video rendered green
+        https://bugs.webkit.org/show_bug.cgi?id=201422
+        <rdar://problem/55945741>
+
+        Reviewed by Carlos Garcia Campos.
+
+        Enable the texture upload GStreamer meta code path. Until
+        GStreamer 1.16.2 this workaround is needed to fix VP9 (vp9dec)
+        rendering. For downstream users cherry-picking the corresponding
+        GStreamer patch[0], an environment variable can be set to bypass
+        the reintroduced slow color conversion: $WEBKIT_GST_NO_RGBA_CONVERSION.
+
+        [0] https://gitlab.freedesktop.org/gstreamer/gst-plugins-base/commit/8d32de090554cf29fe359f83aa46000ba658a693
+
+        * platform/graphics/gstreamer/MediaPlayerPrivateGStreamerBase.cpp:
+        (WebCore::MediaPlayerPrivateGStreamerBase::createVideoSinkGL):
+
 2019-11-06  youenn fablet  <youenn@apple.com>
 
         There is no need to clean the content type header of a request if it is null

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

@@ -1206,8 +1206,33 @@ GstElement* MediaPlayerPrivateGStreamerBase::createVideoSinkGL()
 
     result &= gst_element_link_many(upload, colorconvert, appsink, nullptr);
 
-    GRefPtr<GstPad> pad = adoptGRef(gst_element_get_static_pad(upload, "sink"));
-    gst_element_add_pad(videoSink, gst_ghost_pad_new("sink", pad.get()));
+    // Workaround until we can depend on GStreamer 1.16.2.
+    // https://gitlab.freedesktop.org/gstreamer/gst-plugins-base/commit/8d32de090554cf29fe359f83aa46000ba658a693
+    // Forcing a color conversion to RGBA here allows glupload to internally use
+    // an uploader that adds a VideoMeta, through the TextureUploadMeta caps
+    // feature, without needing the patch above. However this specific caps
+    // feature is going to be removed from GStreamer so it is considered a
+    // short-term workaround. This code path most likely will have a negative
+    // performance impact on embedded platforms as well. Downstream embedders
+    // are highly encouraged to cherry-pick the patch linked above in their BSP
+    // and set the WEBKIT_GST_NO_RGBA_CONVERSION environment variable until
+    // GStreamer 1.16.2 is released.
+    // See also https://bugs.webkit.org/show_bug.cgi?id=201422
+    if (webkitGstCheckVersion(1, 16, 2) || getenv("WEBKIT_GST_NO_RGBA_CONVERSION")) {
+        GRefPtr<GstPad> pad = adoptGRef(gst_element_get_static_pad(upload, "sink"));
+        gst_element_add_pad(videoSink, gst_ghost_pad_new("sink", pad.get()));
+    } else {
+        GstElement* capsFilter = gst_element_factory_make("capsfilter", nullptr);
+        GRefPtr<GstCaps> caps = adoptGRef(gst_caps_from_string("video/x-raw, format=RGBA"));
+        g_object_set(capsFilter, "caps", caps.get(), nullptr);
+
+        GstElement* videoconvert = gst_element_factory_make("videoconvert", nullptr);
+        gst_bin_add_many(GST_BIN_CAST(videoSink), capsFilter, videoconvert, nullptr);
+        result &= gst_element_link_many(capsFilter, videoconvert, upload, nullptr);
+
+        GRefPtr<GstPad> pad = adoptGRef(gst_element_get_static_pad(capsFilter, "sink"));
+        gst_element_add_pad(videoSink, gst_ghost_pad_new("sink", pad.get()));
+    }
 
     if (!result) {
         GST_WARNING("Failed to link GstGL elements");