Introduce CODEC Alpha plugin

This plugin contains a set of utility elements allowing to extract,
decode and combine CODEC (typically VP8/VP9) alpha stream.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/2199>

gst/codecalpha/gstcodecalphademux.c

@@ -0,0 +1,106 @@
+/* GStreamer
+ * Copyright (C) <2021> Collabora Ltd.
+ *   Author: Nicolas Dufresne <nicolas.dufresne@collabora.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Library General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public
+ * License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
+ * Boston, MA 02110-1301, USA.
+ */
+
+/**
+ * SECTION:element-codecalphademux
+ * @title: CODEC Alpha Demuxer
+ *
+ * Extract the CODEC (typically VP8/VP9) alpha stream stored at meta and
+ * expose it as a stream. This element allow using single stream VP9 decoders
+ * in order to decode both streams.
+ *
+ * ## Example launch line
+ * |[
+ * gst-launch-1.0 -v filesrc location=transparency.webm ! matroskademux ! 
+ *     codecalphademux name=d
+ *     d.video ! queue ! vp9dec ! autovideosink
+ *     d.alpha ! queue ! vp9dec ! autovideosink
+ * ]| This pipeline splits and decode the video and the alpha stream, showing
+ *    the result on seperate window.
+ *
+ */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <gst/video/video.h>
+#include "gstcodecalphademux.h"
+
+GST_DEBUG_CATEGORY_STATIC (codecalphademux_debug);
+#define GST_CAT_DEFAULT (codecalphademux_debug)
+
+struct _GstCodecAlphaDemux
+{
+  GstElement parent;
+};
+
+#define gst_codec_alpha_demux_parent_class parent_class
+G_DEFINE_TYPE_WITH_CODE (GstCodecAlphaDemux, gst_codec_alpha_demux, 
+    GST_TYPE_ELEMENT,
+    GST_DEBUG_CATEGORY_INIT (codecalphademux_debug, "codecalphademux", 0,
+        "codecalphademux"));
+
+GST_ELEMENT_REGISTER_DEFINE (codec_alpha_demux, "codecalphademux",
+    GST_RANK_NONE, GST_TYPE_CODEC_ALPHA_DEMUX);
+
+static GstStaticPadTemplate gst_codec_alpha_demux_sink_template =
+GST_STATIC_PAD_TEMPLATE ("sink",
+    GST_PAD_SINK,
+    GST_PAD_ALWAYS,
+    GST_STATIC_CAPS ("ANY")
+    );
+
+static GstStaticPadTemplate gst_codec_alpha_demux_src_template =
+GST_STATIC_PAD_TEMPLATE ("src",
+    GST_PAD_SRC,
+    GST_PAD_ALWAYS,
+    GST_STATIC_CAPS ("ANY")
+    );
+
+static GstStaticPadTemplate gst_codec_alpha_demux_alpha_template =
+GST_STATIC_PAD_TEMPLATE ("alpha",
+    GST_PAD_SRC,
+    GST_PAD_ALWAYS,
+    GST_STATIC_CAPS ("ANY")
+    );
+
+static void
+gst_codec_alpha_demux_class_init (GstCodecAlphaDemuxClass * klass)
+{
+  GstElementClass *element_class = (GstElementClass *) klass;
+
+  gst_element_class_set_static_metadata (element_class,
+      "CODEC Alpha Demuxer", "Codec/Demuxer",
+      "Extract and expose as a stream the CODEC alpha.",
+      "Nicolas Dufresne <nicolas.dufresne@collabora.com>");
+
+  gst_element_class_add_static_pad_template (element_class,
+      &gst_codec_alpha_demux_sink_template);
+  gst_element_class_add_static_pad_template (element_class,
+      &gst_codec_alpha_demux_src_template);
+  gst_element_class_add_static_pad_template (element_class,
+      &gst_codec_alpha_demux_alpha_template);
+}
+
+static void
+gst_codec_alpha_demux_init (GstCodecAlphaDemux * demux)
+{
+}

gst/codecalpha/gstcodecalphademux.h

@@ -0,0 +1,35 @@
+/* GStreamer
+ * Copyright (C) <2021> Collabora Ltd.
+ *   Author: Nicolas Dufresne <nicolas.dufresne@collabora.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Library General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public
+ * License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
+ * Boston, MA 02110-1301, USA.
+ */
+
+#ifndef __GST_CODEC_ALPHA_DEMUX_H__
+#define __GST_CODEC_ALPHA_DEMUX_H__
+
+#include <gst/gst.h>
+
+G_BEGIN_DECLS
+
+#define GST_TYPE_CODEC_ALPHA_DEMUX (gst_codec_alpha_demux_get_type())
+G_DECLARE_FINAL_TYPE (GstCodecAlphaDemux,
+    gst_codec_alpha_demux, GST, CODEC_ALPHA_DEMUX, GstElement);
+
+GST_ELEMENT_REGISTER_DECLARE (codec_alpha_demux);
+
+G_END_DECLS
+#endif

gst/codecalpha/gstplugin.c

@@ -0,0 +1,43 @@
+/* GStreamer
+ * Copyright (C) <2021> Collabora Ltd.
+ *   Author: Nicolas Dufresne <nicolas.dufresne@collabora.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Library General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public
+ * License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
+ * Boston, MA 02110-1301, USA.
+ */
+
+#ifdef HAVE_CONFIG_H
+#  include <config.h>
+#endif
+
+#include <gst/gst.h>
+
+#include "gstcodecalphademux.h"
+
+static gboolean
+plugin_init (GstPlugin * plugin)
+{
+  gboolean ret = FALSE;
+
+  ret |= GST_ELEMENT_REGISTER (codec_alpha_demux, plugin);
+
+  return ret;
+}
+
+GST_PLUGIN_DEFINE (GST_VERSION_MAJOR,
+    GST_VERSION_MINOR,
+    codecalpha,
+    "CODEC Alpha Utilities",
+    plugin_init, VERSION, "LGPL", GST_PACKAGE_NAME, GST_PACKAGE_ORIGIN)

gst/codecalpha/meson.build

@@ -0,0 +1,15 @@
+codecalpha_sources = [
+  'gstplugin.c',
+  'gstcodecalphademux.c',
+]
+
+gstcodecalpha = library('gstcodecalpha',
+  codecalpha_sources,
+  c_args : gst_plugins_bad_args,
+  include_directories : [configinc],
+  dependencies : [gstvideo_dep],
+  install : true,
+  install_dir : plugins_install_dir,
+)
+pkgconfig.generate(gstcodecalpha, install_dir : plugins_pkgconfig_install_dir)
+plugins += [gstcodecalpha]

gst/meson.build

@@ -1,7 +1,7 @@
 foreach plugin : ['accurip', 'adpcmdec', 'adpcmenc', 'aiff', 'asfmux',
                   'audiobuffersplit', 'audiofxbad', 'audiomixmatrix',
                   'audiolatency', 'audiovisualizers', 'autoconvert', 'bayer',
-                  'camerabin2', 'coloreffects', 'debugutils', 'dvbsubenc',
+                  'camerabin2', 'codecalpha', 'coloreffects', 'debugutils', 'dvbsubenc',
                   'dvbsuboverlay', 'dvdspu', 'faceoverlay', 'festival',
                   'fieldanalysis', 'freeverb', 'frei0r', 'gaudieffects', 'gdp',
                   'geometrictransform', 'id3tag', 'inter', 'interlace',

meson_options.txt

@@ -15,6 +15,7 @@ option('audiovisualizers', type : 'feature', value : 'auto')
 option('autoconvert', type : 'feature', value : 'auto')
 option('bayer', type : 'feature', value : 'auto')
 option('camerabin2', type : 'feature', value : 'auto')
+option('codecalpha', type : 'feature', value : 'auto')
 option('coloreffects', type : 'feature', value : 'auto')
 option('debugutils', type : 'feature', value : 'auto')
 option('dvbsubenc', type : 'feature', value : 'auto')