How to program videomixer using Gstreamer C API

[Dejan Tolj]

I am trying to simulate the following gstreamer pipeline using the C API:

gst-launch -e videomixer name=mix ! ffmpegcolorspace ! xvimagesink \
  videotestsrc pattern=1  ! video/x-raw-yuv,width=100,height=100 !
videobox border-alpha=0 top=0 left=0 ! mix. \
  videotestsrc pattern=0  ! video/x-raw-yuv,width=100,height=100 !
videobox border-alpha=0 top=0 left=-100 ! mix.

So far I have:

#include <gst/gst.h>
#include <glib.h>


static gboolean
bus_call (GstBus     *bus,
         GstMessage *msg,
         gpointer    data)
{
 GMainLoop *loop = (GMainLoop *) data;

 switch (GST_MESSAGE_TYPE (msg)) {

   case GST_MESSAGE_EOS:
     g_print ("End of stream\n");
     g_main_loop_quit (loop);
     break;

   case GST_MESSAGE_ERROR: {
     gchar  *debug;
     GError *error;

     gst_message_parse_error (msg, &error, &debug);
     g_free (debug);

     g_printerr ("Error: %s\n", error->message);
     g_error_free (error);

     g_main_loop_quit (loop);
     break;
   }
   default:
     break;
 }

 return TRUE;
}


int
main (int   argc,
     char *argv[])
{
 GMainLoop *loop;

 GstElement *pipeline;
 GstElement *source1,*source2;
 GstElement *scale,*filter;
 GstElement *videobox1,*videobox2; //just one.
 GstElement *mixer,*clrspace,*sink;
 GstCaps *filtercaps;
 GstBus *bus;

 /* Initialisation */
 gst_init (&argc, &argv);

 loop = g_main_loop_new (NULL, FALSE);


 /* Check input arguments */
 /*if (argc != 2) {
   g_printerr ("Usage: %s <Ogg/Vorbis filename>\n", argv[0]);
   return -1;
 }*/

 //gst-launch videotestsrc pattern=snow ! ximagesink

 /* Create gstreamer elements */
 pipeline = gst_pipeline_new ("player");
 source1   = gst_element_factory_make ("videotestsrc",       "source1");
 source2   = gst_element_factory_make ("videotestsrc",       "source2");
//  source2   = gst_element_factory_make ("uridecodebin",       "file-source2");
 scale   = gst_element_factory_make ("videoscale",       "scale");
 filter = gst_element_factory_make("capsfilter","filter");
 videobox1 = gst_element_factory_make ("videobox",       "videobox1");
 videobox2 = gst_element_factory_make ("videobox",       "videobox2");
 mixer = gst_element_factory_make ("videomixer",       "mixer");
 clrspace  = gst_element_factory_make ("ffmpegcolorspace",       "clrspace");

//  demuxer  = gst_element_factory_make ("oggdemux",      "ogg-demuxer");
//  decoder  = gst_element_factory_make ("vorbisdec",     "vorbis-decoder");
//  conv     = gst_element_factory_make ("audioconvert",  "converter");
 sink     = gst_element_factory_make ("xvimagesink", "sink");

 /*if (!pipeline || !source || !demuxer || !decoder || !conv || !sink) {
   g_printerr ("One element could not be created. Exiting.\n");
   return -1;
 }*/
 if (!pipeline || !source1 || !source2 || !sink) {
   g_printerr ("One element could not be created. Exiting.\n");
   return -1;
 }

 filtercaps = gst_caps_new_simple ("video/x-raw-yuv",
         "width", G_TYPE_INT, 200,
         "height", G_TYPE_INT, 100,
         NULL);
 g_object_set (G_OBJECT (filter), "caps", filtercaps, NULL);
 //gst_caps_unref (filtercaps);

 g_object_set(videobox1,"border-alpha",0,"top",0,"left",0,NULL);
 g_object_set(videobox2,"border-alpha",0,"top",0,"left",-200,NULL);


 /* Set up the pipeline */

 /* we set the input filename to the source element */
   g_object_set (G_OBJECT (source1), "pattern", 0, NULL);
   g_object_set (G_OBJECT (source2), "pattern", 1, NULL);

 /* we add a message handler */
 bus = gst_pipeline_get_bus (GST_PIPELINE (pipeline));
 gst_bus_add_watch (bus, bus_call, loop);
 gst_object_unref (bus);

 /* we add all elements into the pipeline */
 gst_bin_add_many (GST_BIN (pipeline),
                   source1,filter,videobox1,mixer,clrspace, sink,
source2,videobox2, NULL);

 /* we link the elements together */
   //gst_element_link_many (source1, scale, filter, videobox1, mixer,
clrspace, sink);
   //gst_element_link_many (source2, scale, filter, videobox2, mixer,
clrspace, sink);
   gst_element_link_many (source1, filter, videobox1, mixer, clrspace, sink);
   gst_element_link_many (source2, filter, videobox2, mixer, clrspace, sink);


 /* Set the pipeline to "playing" state*/
 gst_element_set_state (pipeline, GST_STATE_PLAYING);

 /* Iterate */
 g_print ("Running...\n");
 g_main_loop_run (loop);

 /* Out of the main loop, clean up nicely */
 g_print ("Returned, stopping playback\n");
 gst_element_set_state (pipeline, GST_STATE_NULL);

 g_print ("Deleting pipeline\n");
 gst_object_unref (GST_OBJECT (pipeline));

 return 0;
}


I have also set debugging on: export GST_DEBUG=3

When I run my program I get the following error:

Running...
0:00:00.178663884  4797  0x8937020 WARN                 basesrc
gstbasesrc.c:2582:gst_base_src_loop:<source2> error: Internal data
flow error.
0:00:00.178766444  4797  0x8937020 WARN                 basesrc
gstbasesrc.c:2582:gst_base_src_loop:<source2> error: streaming task
paused, reason not-linked (-1)
Error: Internal data flow error.
Returned, stopping playback
0:00:00.202571746  4797  0x893ae00 WARN           basetransform
gstbasetransform.c:1627:gst_base_transform_prepare_output_buffer:<clrspace>
pad-alloc failed: wrong-state
0:00:00.202645907  4797  0x893ae00 WARN           basetransform
gstbasetransform.c:2335:gst_base_transform_handle_buffer:<clrspace>
could not get buffer from pool: wrong-state
Deleting pipeline


Why is it complaining about source2 not-linked?