From 12f082f7cf80c47f3b124976adbed8b4889d4c86 Mon Sep 17 00:00:00 2001
From: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Date: Fri, 4 Mar 2022 10:02:56 -0500
Subject: [PATCH] vp9parse: Fix auto-plugging of HW frame decoder

Decoders that required frame aligmment and didn't have an associated
alpha decoder were skipped. This is because the parser was constructing
caps based on the software alpha decoder, which specify super-frame
alignment.

Iterate over the caps to filter the one that have a matching codec-alpha, with
the semantic the no codec-alpha field means codec-alpha=false. Then if
everything was removed, callback to the original, so that the first non-alpha
decoder will be picked.

Fixes #820

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/1949>
---
 .../gst/videoparsers/gstvp9parse.c            | 39 ++++++++++++++++---
 1 file changed, 33 insertions(+), 6 deletions(-)

diff --git a/subprojects/gst-plugins-bad/gst/videoparsers/gstvp9parse.c b/subprojects/gst-plugins-bad/gst/videoparsers/gstvp9parse.c
index 81b2879842..4b73bc15ce 100644
--- a/subprojects/gst-plugins-bad/gst/videoparsers/gstvp9parse.c
+++ b/subprojects/gst-plugins-bad/gst/videoparsers/gstvp9parse.c
@@ -51,6 +51,7 @@ struct _GstVp9Parse
   GstVp9ColorRange color_range;
   GstVP9Profile profile;
   GstVp9BitDepth bit_depth;
+  gboolean codec_alpha;
 
   GstVp9ParseAligment in_align;
   GstVp9ParseAligment align;
@@ -133,6 +134,7 @@ gst_vp9_parse_reset (GstVp9Parse * self)
   self->color_range = GST_VP9_CR_LIMITED;
   self->profile = GST_VP9_PROFILE_UNDEFINED;
   self->bit_depth = (GstVp9BitDepth) 0;
+  self->codec_alpha = FALSE;
 }
 
 static gboolean
@@ -245,6 +247,18 @@ gst_vp9_parse_alignment_from_caps (GstCaps * caps, GstVp9ParseAligment * align)
   }
 }
 
+/* implement custom semantic for codec-alpha */
+static gboolean
+gst_vp9_parse_check_codec_alpha (GstStructure * s, gboolean codec_alpha)
+{
+  gboolean value;
+
+  if (gst_structure_get_boolean (s, "codec-alpha", &value))
+    return value == codec_alpha;
+
+  return codec_alpha == FALSE;
+}
+
 /* check downstream caps to configure format and alignment */
 static void
 gst_vp9_parse_negotiate (GstVp9Parse * self, GstVp9ParseAligment in_align,
@@ -259,6 +273,23 @@ gst_vp9_parse_negotiate (GstVp9Parse * self, GstVp9ParseAligment in_align,
   /* concentrate on leading structure, since decodebin parser
    * capsfilter always includes parser template caps */
   if (caps) {
+    while (gst_caps_get_size (caps) > 0) {
+      GstStructure *s = gst_caps_get_structure (caps, 0);
+
+      if (gst_vp9_parse_check_codec_alpha (s, self->codec_alpha))
+        break;
+
+      gst_caps_remove_structure (caps, 0);
+    }
+
+    /* this may happen if there is simply no codec alpha decoder in the
+     * gstreamer installation, in this case, pick the first non-alpha decoder.
+     */
+    if (gst_caps_is_empty (caps)) {
+      gst_caps_unref (caps);
+      caps = gst_pad_get_allowed_caps (GST_BASE_PARSE_SRC_PAD (self));
+    }
+
     caps = gst_caps_truncate (caps);
     GST_DEBUG_OBJECT (self, "negotiating with caps: %" GST_PTR_FORMAT, caps);
   }
@@ -503,7 +534,6 @@ gst_vp9_parse_update_src_caps (GstVp9Parse * self, GstCaps * caps)
   gchar *colorimetry = NULL;
   const gchar *chroma_format = NULL;
   const gchar *profile = NULL;
-  gboolean codec_alpha_allowed = FALSE;
 
   if (!self->update_caps)
     return;
@@ -548,10 +578,6 @@ gst_vp9_parse_update_src_caps (GstVp9Parse * self, GstCaps * caps)
     gst_structure_get_fraction (s, "framerate", &fps_n, &fps_d);
   }
 
-  if (s && gst_structure_has_field (s, "codec-alpha")) {
-    gst_structure_get_boolean (s, "codec-alpha", &codec_alpha_allowed);
-  }
-
   if (fps_n > 0 && fps_d > 0) {
     gst_caps_set_simple (final_caps, "framerate",
         GST_TYPE_FRACTION, fps_n, fps_d, NULL);
@@ -660,7 +686,7 @@ gst_vp9_parse_update_src_caps (GstVp9Parse * self, GstCaps * caps)
     gst_caps_set_simple (final_caps, "profile", G_TYPE_STRING, profile, NULL);
 
   gst_caps_set_simple (final_caps, "codec-alpha", G_TYPE_BOOLEAN,
-      codec_alpha_allowed, NULL);
+      self->codec_alpha, NULL);
 
   src_caps = gst_pad_get_current_caps (GST_BASE_PARSE_SRC_PAD (self));
 
@@ -723,6 +749,7 @@ gst_vp9_parse_set_sink_caps (GstBaseParse * parse, GstCaps * caps)
   profile = gst_structure_get_string (str, "profile");
   if (profile)
     self->profile = gst_vp9_parse_profile_from_string (profile);
+  gst_structure_get_boolean (str, "codec-alpha", &self->codec_alpha);
 
   /* get upstream align from caps */
   gst_vp9_parse_alignment_from_caps (caps, &align);