How to program videomixer using Gstreamer C API - c

Question

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?

Answer 1

A little late, but may be helpful:
If you look at the documentation for the videomixer element, you'll see that videomixer's sink pads are request pads. You need to create these pads before linking them.
/* Manually link the mixer, which has "Request" pads */
mixer_sink_pad_template = gst_element_class_get_pad_template (GST_ELEMENT_GET_CLASS (mixer), "sink_%u");
mixer_sink_pad = gst_element_request_pad (mixer, mixer_sink_pad_template, NULL, NULL);
sink_pad = gst_element_get_static_pad (clrspace, "src");
gst_pad_link ( sink_pad,mixer_sink_pad);
Similarly request pads are created for as many streams as you want.

Answer 2

gst_element_link_many (source1, filter, videobox1, mixer, clrspace, sink, NULL);
gst_element_link_many (source2, filter, videobox2, mixer, NULL);
Please also learn about the x,y,z properties on videomixerpad, you can spare the videobox elements this way and gain performance