examples: Add a compositor mosaic example.

Add an example of configuring compositor to display 2 videos
side-by-side in a mosaic, and additionally configure some
video-converter properties to demonstrate how that works..

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-base/-/merge_requests/919>

tests/examples/compositor/meson.build

@@ -4,6 +4,12 @@ executable('crossfade', 'crossfade.c',
   dependencies: [gst_controller_dep, gst_dep],
   install: false)
 
+executable('mosaic', 'mosaic.c',
+  include_directories: [configinc],
+  c_args: ['-DHAVE_CONFIG_H'],
+  dependencies: [video_dep, gst_dep],
+  install: false)
+
 executable('signals', 'signals.c',
   include_directories: [configinc],
   c_args: ['-DHAVE_CONFIG_H'],

tests/examples/compositor/mosaic.c

@@ -0,0 +1,141 @@
+/*
+ * GStreamer
+ * Copyright (C) 2017 Thibault Saunier <thibault.saunier@osg-samsung.com>
+ * Copyright (C) 2020 Jan Schmidt <jan@centricular.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.
+ */
+
+/**
+ * Simple example using the compositor element.
+ *
+ * Takes two video files and display them side-by-side as a mosaic
+ */
+
+#include <stdlib.h>
+#include <gst/gst.h>
+#include <gst/video/video.h>
+
+typedef struct
+{
+  GstElement *compositor;
+  gint x, y, w, h;
+  gint zorder;
+} VideoInfo;
+
+static gchar *
+ensure_uri (const gchar * location)
+{
+  if (gst_uri_is_valid (location))
+    return g_strdup (location);
+  else
+    return gst_filename_to_uri (location, NULL);
+}
+
+static void
+_pad_added_cb (GstElement * decodebin, GstPad * pad, VideoInfo * info)
+{
+  GstStructure *converter_config;
+  GstPad *sinkpad =
+      gst_element_get_request_pad (GST_ELEMENT (info->compositor), "sink_%u");
+
+  converter_config = gst_structure_new ("GstVideoConverter",
+      GST_VIDEO_CONVERTER_OPT_THREADS, G_TYPE_UINT, 0,
+      GST_VIDEO_CONVERTER_OPT_RESAMPLER_METHOD, GST_TYPE_VIDEO_RESAMPLER_METHOD,
+      GST_VIDEO_RESAMPLER_METHOD_NEAREST, GST_VIDEO_CONVERTER_OPT_DEST_X,
+      G_TYPE_INT, 0, GST_VIDEO_CONVERTER_OPT_DEST_Y, G_TYPE_INT, 0,
+      GST_VIDEO_CONVERTER_OPT_DEST_WIDTH, G_TYPE_INT, info->w,
+      GST_VIDEO_CONVERTER_OPT_DEST_HEIGHT, G_TYPE_INT, info->h, NULL);
+
+  g_object_set (sinkpad, "xpos", info->x, "ypos", info->y, "width", info->w,
+      "height", info->h, "converter-config", converter_config, NULL);
+
+  gst_structure_free (converter_config);
+
+  gst_pad_link (pad, sinkpad);
+
+  g_free (info);
+}
+
+int
+main (int argc, char *argv[])
+{
+  gint i;
+  GstMessage *message;
+  GstElement *compositor, *pipeline;
+  GstBus *bus;
+
+  if (argc != 3) {
+    g_error ("Need to provide 2 input videos");
+    return -1;
+  }
+
+  gst_init (&argc, &argv);
+  pipeline =
+      gst_parse_launch
+      ("videotestsrc pattern=black is-live=true !  video/x-raw,width=1,height=1,format=AYUV ! compositor name=comp start-time-selection=first ! video/x-raw,format=AYUV,width=1275,height=833,framerate=25/1 ! videoconvert ! autovideosink",
+      NULL);
+
+  g_assert (pipeline != NULL);
+  compositor = gst_bin_get_by_name (GST_BIN (pipeline), "comp");
+
+  gst_util_set_object_arg (G_OBJECT (compositor), "background", "black");
+
+  for (i = 1; i < 3; i++) {
+    gchar *uri = ensure_uri (argv[i]);
+    VideoInfo *info = g_malloc0 (sizeof (VideoInfo));
+    GstElement *uridecodebin = gst_element_factory_make ("uridecodebin", NULL);
+
+    g_object_set (uridecodebin, "uri", uri, "expose-all-streams", FALSE,
+        "caps", gst_caps_from_string ("video/x-raw(ANY)"), NULL);
+
+    info->compositor = compositor;
+    if (i == 1) {
+      info->x = 326;
+      info->y = 155;
+      info->w = 930;
+      info->h = 523;
+      info->zorder = 2;
+    } else {
+      info->x = 19;
+      info->y = 155;
+      info->w = 288;
+      info->h = 162;
+      info->zorder = 3;
+    }
+    g_signal_connect (uridecodebin, "pad-added", (GCallback) _pad_added_cb,
+        info);
+
+    gst_bin_add (GST_BIN (pipeline), uridecodebin);
+  }
+
+  bus = gst_element_get_bus (pipeline);
+  gst_element_set_state (pipeline, GST_STATE_PLAYING);
+
+  message =
+      gst_bus_timed_pop_filtered (bus, 60 * GST_SECOND,
+      GST_MESSAGE_EOS | GST_MESSAGE_ERROR);
+  GST_DEBUG_BIN_TO_DOT_FILE_WITH_TS (GST_BIN (pipeline),
+      GST_DEBUG_GRAPH_SHOW_ALL | GST_DEBUG_GRAPH_SHOW_VERBOSE, "go");
+  if (message)
+    gst_print ("%" GST_PTR_FORMAT "\n", message);
+  else
+    gst_print ("Timeout\n");
+  gst_element_set_state (pipeline, GST_STATE_NULL);
+  gst_object_unref (pipeline);
+
+  return 0;
+}