why is gstreamer caps is blocking pipeline - gstreamer

Question

I am trying a basic pipeline below. If I run the pipeline without the caps function it passes straight through (assuming same I/O format). Once I add the caps the pre-roll starts but the video does not continue through to the sink output.
Am I coding this wrong?
thx
Art
#include <gst/gst.h>
#include <glib.h>
static void
on_pad_added (GstElement *element,
GstPad *pad,
gpointer data)
{
GstPad *sinkpad;
GstElement *decoder = (GstElement *) data;
g_print ("Dynamic pad created, linking out/in \n");
sinkpad = gst_element_get_static_pad (decoder, "sink");
gst_pad_link (pad, sinkpad);
gst_object_unref (sinkpad);
}
int
main (int argc,
char *argv[])
{
GMainLoop *loop;
gboolean link_ok;
GstElement *pipeline, *source, *decoder, *ffcs, *vidsc, *capsfout, *sink;
GstBus *bus;
GstCaps *caps;
/* Initialisation */
gst_init (&argc, &argv);
loop = g_main_loop_new (NULL, FALSE);
/* Create gstreamer elements */
pipeline = gst_pipeline_new ("video-player");
source = gst_element_factory_make ("filesrc", "file-source");
decoder = gst_element_factory_make ("decodebin2", "dec-bin2");
ffcs = gst_element_factory_make ("ffmpegcolorspace", "ffcs");
vidsc = gst_element_factory_make ("videoscale", "vidsc");
capsfout = gst_element_factory_make ("capsfilter", "capsfout");
sink = gst_element_factory_make ("filesink", "vidout");
if (!pipeline || !source || !decoder || !ffcs || !vidsc || !capsfout || !sink) {
g_printerr ("One element could not be created. Exiting.\n");
return -1;
}
/* we set the input/output filename to the source element */
g_object_set (G_OBJECT (source), "location", argv[1], NULL);
g_object_set (G_OBJECT (sink), "location", argv[2], NULL);
bus = gst_pipeline_get_bus (GST_PIPELINE (pipeline));
gst_bin_add_many (GST_BIN (pipeline),
source, decoder, ffcs, vidsc, capsfout, sink, NULL);
/* we link the elements together */
gst_element_link (source, decoder);
gst_element_link (decoder, ffcs);
gst_element_link (ffcs, vidsc);
caps = gst_caps_new_simple("video/x-raw-yuv",
"format", GST_TYPE_FOURCC, GST_MAKE_FOURCC ('I', '4', '2', '0'),
"width", G_TYPE_INT, 384,
"height", G_TYPE_INT, 216,
"framerate", GST_TYPE_FRACTION, 25, 1,
NULL);
link_ok = gst_element_link_filtered(vidsc,sink,caps);
gst_caps_unref (caps);
if (!link_ok) {
g_warning ("Failed to link vidsc to sink!");
}else{
g_print("seems ok, no error reported?\n");
}
/* Set the pipeline to "playing" state*/
g_print ("Now playing: %s\n", argv[1]);
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;
}

Answer 1

It may be late to answer but you maybe forgot to do the dynamic pad link between some elements and you never call the on_pad_added function. I had the same problem.
Have you tried to add it since then? For example this line to dynamically link two elements instead of the gst_element_link:
g_signal_connect (decoder, "pad-added", G_CALLBACK (on_pad_added), ffcs);

Answer 2

For what reasons do you need the capsfilter? Only constrain the properties you need. E.g. you set a framerate, but don't have a videorate element before the capsfilter. If you don't care about the framerate (e.g. just want to force a size) remove the framerate from the caps you set on capsfilter..