Writing a streamer application which generates UYVY frames.

[Nick.Adamson at gdlsuk.com]

Hi All.
I'm new to this list and GStreamer and would like some advice please.
I've been reading the GStreamer guide from http://gstreamer.freedesktop.org/data/doc/gstreamer/head/manual/html/index.html and have written a couple of basic applications which have worked OK.

What I'd like to do is update my application, which currently reads a file and plays it, to give me access to a UYVY frame for each frame of the video.

See below for code snippets I'm using, which is mostly based on the playsink example given in chapter 20 of the guide, http://gstreamer.freedesktop.org/data/doc/gstreamer/head/manual/html/section-components-playsink.html.

I've come across the video converter element which is able to output UYVY formatted video however I'm unsure how to link this in to my pipeline as it's using a dynamic sink. The documentation for the videoconverter is here: http://gstreamer.freedesktop.org/data/doc/gstreamer/head/gst-plugins-base-plugins/html/gst-plugins-base-plugins-videoconvert.html
I've read this a number of times but am unsure how to link the extra element in and how to set the sink pad to be a UYVY format.

Once I've converted the video how do I get access to the frames? Is there a sink I can use to send the frames in to the application space or do I need to get access to the buffer? If so how?

Not that it should matter but I'm developing in c++ on windows.
Code:
... snip ...
// Globals
GstElement *pipeline, *sink;

static void cb_pad_added (GstElement *dec,      GstPad *pad,     gpointer data)
{
  GstCaps *caps;
  GstStructure *str;
  const gchar *name;
  GstPadTemplate *templ;
  GstElementClass *klass;

  // check media type
  caps = gst_pad_query_caps (pad, NULL);
  str = gst_caps_get_structure (caps, 0);
  name = gst_structure_get_name (str);
  klass = GST_ELEMENT_GET_CLASS (sink);
  if (g_str_has_prefix (name, "audio"))
  {
    templ = gst_element_class_get_pad_template (klass, "audio_sink");
  }
  else if (g_str_has_prefix (name, "video"))
  {
    templ = gst_element_class_get_pad_template (klass, "video_sink");
  }
  else if (g_str_has_prefix (name, "text"))
  {
    templ = gst_element_class_get_pad_template (klass, "text_sink");
  }
  else
  {
    templ = NULL;
  }
  if (templ)
  {
    GstPad *sinkpad;
    sinkpad = gst_element_request_pad (sink, templ, NULL, NULL);
    if (!gst_pad_is_linked (sinkpad))
    {
      gst_pad_link (pad, sinkpad);
    }
    gst_object_unref (sinkpad);
  }
}

int main(int argc, char** argv)
{
.... snipped ....

  // initialise gstreamer and get version information.
  const gchar *nano_str;
  guint major, minor, micro, nano;
  gst_init(&argc, &argv);

  // get the version of gstreamer.
  gst_version(&major, &minor, &micro, &nano);
  if (nano == 1)
  {
    nano_str = "(CVS)";
  }
  else if (nano == 2)
  {
    nano_str = "(Prerelease)";
  }
  else
  { nano_str = "";
  }
  char cVersion[256];
  sprintf(cVersion, "This program is linked against GStreamer %d.%d.%d %s",
    major, minor, micro, nano_str);
  print( cVersion );

  GMainLoop *loop;
  GstElement *dec;
  GstBus *bus;
  loop = g_main_loop_new (NULL, FALSE);

  // setup
  pipeline = gst_pipeline_new ("pipeline");
  bus = gst_pipeline_get_bus (GST_PIPELINE (pipeline));
  gst_bus_add_watch (bus, bus_call, loop);
  gst_object_unref (bus);

  dec = gst_element_factory_make ("uridecodebin", "source");
  g_object_set (G_OBJECT (dec), "uri", argv[1],
    NULL);
  g_signal_connect (dec, "pad-added", G_CALLBACK (cb_pad_added), NULL);

  // create audio output
  sink = gst_element_factory_make ("playsink", "sink");
  gst_util_set_object_arg (G_OBJECT (sink), "flags",
    "soft-colorbalance+soft-volume+vis+text+audio+video");
  gst_bin_add_many (GST_BIN (pipeline), dec, sink, NULL);

  // run
  gst_element_set_state (pipeline, GST_STATE_PLAYING);
  g_main_loop_run (loop);

  // cleanup
  gst_element_set_state (pipeline, GST_STATE_NULL);
  gst_object_unref (GST_OBJECT (pipeline));

  print("all done.");
  fclose( gLogFile );
  gLogFile = NULL;
  return 0;
}
... end of code. ...

Thanks for any ideas and sorry for all the noddy questions.
Nick.
Nick Adamson
Software Engineer

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