v4l2codecs: vp9: Add alpha decodebin wrapper

This will allow HW accelerated decoding of WebM alpha videos.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/1439>

subprojects/gst-plugins-bad/sys/v4l2codecs/gstv4l2codecvp9dec.c

@@ -23,6 +23,7 @@
 #endif
 
 #include "gstv4l2codecallocator.h"
+#include "gstv4l2codecalphadecodebin.h"
 #include "gstv4l2codecpool.h"
 #include "gstv4l2codecvp9dec.h"
 #include "linux/v4l2-controls.h"
@@ -46,6 +47,13 @@ GST_STATIC_PAD_TEMPLATE (GST_VIDEO_DECODER_SINK_NAME,
     GST_STATIC_CAPS ("video/x-vp9, " "alignment=(string) frame")
     );
 
+static GstStaticPadTemplate alpha_template =
+GST_STATIC_PAD_TEMPLATE (GST_VIDEO_DECODER_SINK_NAME,
+    GST_PAD_SINK, GST_PAD_ALWAYS,
+    GST_STATIC_CAPS ("video/x-vp9, codec-alpha = (boolean) true, "
+        "alignment = frame")
+    );
+
 static GstStaticPadTemplate src_template =
 GST_STATIC_PAD_TEMPLATE (GST_VIDEO_DECODER_SRC_NAME,
     GST_PAD_SRC, GST_PAD_ALWAYS,
@@ -1100,13 +1108,58 @@ gst_v4l2_codec_vp9_dec_subclass_init (GstV4l2CodecVp9DecClass * klass,
   gst_v4l2_decoder_install_properties (gobject_class, PROP_LAST, device);
 }
 
+static void gst_v4l2_codec_vp9_alpha_decode_bin_subclass_init
+    (GstV4l2CodecAlphaDecodeBinClass * klass, gchar * decoder_name)
+{
+  GstV4l2CodecAlphaDecodeBinClass *adbin_class =
+      (GstV4l2CodecAlphaDecodeBinClass *) klass;
+  GstElementClass *element_class = (GstElementClass *) klass;
+
+  adbin_class->decoder_name = decoder_name;
+  gst_element_class_add_static_pad_template (element_class, &alpha_template);
+
+  gst_element_class_set_static_metadata (element_class,
+      "VP9 Alpha Decoder", "Codec/Decoder/Video",
+      "Wrapper bin to decode VP9 with alpha stream.",
+      "Nicolas Dufresne <nicolas.dufresne@collabora.com>");
+}
+
 void
-gst_v4l2_codec_vp9_dec_register (GstPlugin * plugin,
+gst_v4l2_codec_vp9_dec_register (GstPlugin * plugin, GstV4l2Decoder * decoder,
     GstV4l2CodecDevice * device, guint rank)
 {
+  gchar *element_name;
+  GstCaps *src_caps, *alpha_caps;
+
+  if (!gst_v4l2_decoder_set_sink_fmt (decoder, V4L2_PIX_FMT_VP9_FRAME,
+          320, 240, 8))
+    return;
+  src_caps = gst_v4l2_decoder_enum_src_formats (decoder);
+
+  if (gst_caps_is_empty (src_caps)) {
+    GST_WARNING ("Not registering VP9 decoder since it produces no "
+        "supported format");
+    goto done;
+  }
+
   gst_v4l2_decoder_register (plugin, GST_TYPE_V4L2_CODEC_VP9_DEC,
       (GClassInitFunc) gst_v4l2_codec_vp9_dec_subclass_init,
       gst_mini_object_ref (GST_MINI_OBJECT (device)),
       (GInstanceInitFunc) gst_v4l2_codec_vp9_dec_subinit,
-      "v4l2sl%svp9dec", device, rank, NULL);
+      "v4l2sl%svp9dec", device, rank, &element_name);
+
+  if (!element_name)
+    goto done;
+
+  alpha_caps = gst_caps_from_string ("video/x-raw,format={I420, NV12}");
+
+  if (gst_caps_can_intersect (src_caps, alpha_caps))
+    gst_v4l2_codec_alpha_decode_bin_register (plugin,
+        (GClassInitFunc) gst_v4l2_codec_vp9_alpha_decode_bin_subclass_init,
+        element_name, "v4l2slvp9%salphadecodebin", device, rank);
+
+  gst_caps_unref (alpha_caps);
+
+done:
+  gst_caps_unref (src_caps);
 }

subprojects/gst-plugins-bad/sys/v4l2codecs/gstv4l2codecvp9dec.h

@@ -46,6 +46,7 @@ struct _GstV4l2CodecVp9DecClass
 
 GType gst_v4l2_codec_vp9_dec_get_type (void);
 void  gst_v4l2_codec_vp9_dec_register (GstPlugin * plugin,
+                                       GstV4l2Decoder * decoder,
                                        GstV4l2CodecDevice * device,
                                        guint rank);
 

subprojects/gst-plugins-bad/sys/v4l2codecs/plugin.c

@@ -69,7 +69,8 @@ register_video_decoder (GstPlugin * plugin, GstV4l2CodecDevice * device)
       case V4L2_PIX_FMT_VP9_FRAME:
         GST_INFO_OBJECT (decoder, "Registering %s as VP9 Decoder",
             device->name);
-        gst_v4l2_codec_vp9_dec_register (plugin, device, GST_RANK_PRIMARY + 1);
+        gst_v4l2_codec_vp9_dec_register (plugin, decoder, device,
+            GST_RANK_PRIMARY + 1);
         break;
 
       default: