Newbie question: Basic Tutorial #3 (Dynamic Pipelines)

[Mike Grommet]

So, I've been walking through the tutorials and trying to work out the 
exercises for my own edification.

The exercise:

Dynamic pad linking has traditionally been a difficult topic for a lot 
of programmers. Prove that you have achieved its mastery by 
instantiating an autovideosink (probably with an ffmpegcolorspace in 
front) and link it to the demuxer when the right pad appears. Hint: You 
are already printing on screen the type of the video pads.

So, I've played around with this and am kind of stuck.  It sure seems 
like I need to add a tee to the pipeline, then attach the audio 
converter and video converter.

But the basic tutorial #3 doesn't really seem to mention tees (they 
aren't mentioned in the tutorial at all until basic tutorial 7).

Am I barking up the wrong tree here?  Anyone have the solved exercise 
that they can pass on?  It feels like cheating, but hey, I'd love to see 
'the right way'


Here's the original Tuturial code for v.10

#include <gst/gst.h>

/* Structure to contain all our information, so we can pass it to 
callbacks */
typedef struct _CustomData {
   GstElement *pipeline;
   GstElement *source;
   GstElement *convert;
   GstElement *sink;
} CustomData;

/* Handler for the pad-added signal */
static void pad_added_handler (GstElement *src, GstPad *pad, CustomData 
*data);

int main(int argc, char *argv[]) {
   CustomData data;
   GstBus *bus;
   GstMessage *msg;
   GstStateChangeReturn ret;
   gboolean terminate = FALSE;

   /* Initialize GStreamer */
   gst_init (&argc, &argv);

   /* Create the elements */
   data.source = gst_element_factory_make ("uridecodebin", "source");
   data.convert = gst_element_factory_make ("audioconvert", "convert");
   data.sink = gst_element_factory_make ("autoaudiosink", "sink");

   /* Create the empty pipeline */
   data.pipeline = gst_pipeline_new ("test-pipeline");

   if (!data.pipeline || !data.source || !data.convert || !data.sink) {
     g_printerr ("Not all elements could be created.\n");
     return -1;
   }

   /* Build the pipeline. Note that we are NOT linking the source at this
    * point. We will do it later. */
   gst_bin_add_many (GST_BIN (data.pipeline), data.source, data.convert 
, data.sink, NULL);
   if (!gst_element_link (data.convert, data.sink)) {
     g_printerr ("Elements could not be linked.\n");
     gst_object_unref (data.pipeline);
     return -1;
   }

   /* Set the URI to play */
   g_object_set (data.source, "uri", 
"http://docs.gstreamer.com/media/sintel_trailer-480p.webm", NULL);

   /* Connect to the pad-added signal */
   g_signal_connect (data.source, "pad-added", G_CALLBACK 
(pad_added_handler), &data);

   /* Start playing */
   ret = gst_element_set_state (data.pipeline, GST_STATE_PLAYING);
   if (ret == GST_STATE_CHANGE_FAILURE) {
     g_printerr ("Unable to set the pipeline to the playing state.\n");
     gst_object_unref (data.pipeline);
     return -1;
   }

   /* Listen to the bus */
   bus = gst_element_get_bus (data.pipeline);
   do {
     msg = gst_bus_timed_pop_filtered (bus, GST_CLOCK_TIME_NONE,
         GST_MESSAGE_STATE_CHANGED | GST_MESSAGE_ERROR | GST_MESSAGE_EOS);

     /* Parse message */
     if (msg != NULL) {
       GError *err;
       gchar *debug_info;

       switch (GST_MESSAGE_TYPE (msg)) {
         case GST_MESSAGE_ERROR:
           gst_message_parse_error (msg, &err, &debug_info);
           g_printerr ("Error received from element %s: %s\n", 
GST_OBJECT_NAME (msg->src), err->message);
           g_printerr ("Debugging information: %s\n", debug_info ? 
debug_info : "none");
           g_clear_error (&err);
           g_free (debug_info);
           terminate = TRUE;
           break;
         case GST_MESSAGE_EOS:
           g_print ("End-Of-Stream reached.\n");
           terminate = TRUE;
           break;
         case GST_MESSAGE_STATE_CHANGED:
           /* We are only interested in state-changed messages from the 
pipeline */
           if (GST_MESSAGE_SRC (msg) == GST_OBJECT (data.pipeline)) {
             GstState old_state, new_state, pending_state;
             gst_message_parse_state_changed (msg, &old_state, 
&new_state, &pending_state);
             g_print ("Pipeline state changed from %s to %s:\n",
                 gst_element_state_get_name (old_state), 
gst_element_state_get_name (new_state));
           }
           break;
         default:
           /* We should not reach here */
           g_printerr ("Unexpected message received.\n");
           break;
       }
       gst_message_unref (msg);
     }
   } while (!terminate);

   /* Free resources */
   gst_object_unref (bus);
   gst_element_set_state (data.pipeline, GST_STATE_NULL);
   gst_object_unref (data.pipeline);
   return 0;
}

/* This function will be called by the pad-added signal */
static void pad_added_handler (GstElement *src, GstPad *new_pad, 
CustomData *data) {
   GstPad *sink_pad = gst_element_get_static_pad (data->convert, "sink");
   GstPadLinkReturn ret;
   GstCaps *new_pad_caps = NULL;
   GstStructure *new_pad_struct = NULL;
   const gchar *new_pad_type = NULL;

   g_print ("Received new pad '%s' from '%s':\n", GST_PAD_NAME 
(new_pad), GST_ELEMENT_NAME (src));

   /* If our converter is already linked, we have nothing to do here */
   if (gst_pad_is_linked (sink_pad)) {
     g_print ("  We are already linked. Ignoring.\n");
     goto exit;
   }

   /* Check the new pad's type */
   new_pad_caps = gst_pad_get_caps (new_pad);
   new_pad_struct = gst_caps_get_structure (new_pad_caps, 0);
   new_pad_type = gst_structure_get_name (new_pad_struct);
   if (!g_str_has_prefix (new_pad_type, "audio/x-raw")) {
     g_print ("  It has type '%s' which is not raw audio. Ignoring.\n", 
new_pad_type);
     goto exit;
   }

   /* Attempt the link */
   ret = gst_pad_link (new_pad, sink_pad);
   if (GST_PAD_LINK_FAILED (ret)) {
     g_print ("  Type is '%s' but link failed.\n", new_pad_type);
   } else {
     g_print ("  Link succeeded (type '%s').\n", new_pad_type);
   }

exit:
   /* Unreference the new pad's caps, if we got them */
   if (new_pad_caps != NULL)
     gst_caps_unref (new_pad_caps);

   /* Unreference the sink pad */
   gst_object_unref (sink_pad);
}



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