gst-basic-tutorial-1/basic-tutorial-3.c

#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 *resample;
    GstElement *sink;
} CustomData;

static void pad_added_handler(GstElement *src, GstPad *new_pad,CustomData *data);

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

    gst_init(&argc,&argv);

    data.source = gst_element_factory_make("uridecodebin","source");
    data.convert = gst_element_factory_make("audioconvert","convert");
    data.resample = gst_element_factory_make("audioresample","resample");
    data.sink = gst_element_factory_make("autoaudiosink","sink");

    data.pipeline = gst_pipeline_new("test-pipeline");

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

    gst_bin_add_many(GST_BIN(data.pipeline),data.source,data.convert,data.resample,data.sink,NULL);
    if(!gst_element_link_many(data.convert,data.resample,data.sink,NULL))
    {
        g_printerr("Elements could not be linked.\n");
        gst_object_unref(data.pipeline);
        return -1;
    }

    g_object_set(data.source,"uri","https://www.freedesktop.org/software/gstreamer-sdk/data/media/sintel_trailer-480p.webm",NULL);

    g_signal_connect(data.source,"pad-added",G_CALLBACK(pad_added_handler),&data);

    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;
    }

    bus = gst_element_get_bus(data.pipeline);
    do {
        message = gst_bus_timed_pop_filtered(bus,GST_CLOCK_TIME_NONE,GST_MESSAGE_STATE_CHANGED | GST_MESSAGE_ERROR | GST_MESSAGE_EOS);

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

            switch(GST_MESSAGE_TYPE(message))
            {
                case GST_MESSAGE_ERROR:
                    gst_message_parse_error(message,&err,&debug_info);
                    g_printerr("Error recevied from element %s:%s\n",GST_OBJECT_NAME(message->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_printerr("End-Of-Stream reached.\n");
                    terminate = TRUE;
                    break;
                case GST_MESSAGE_STATE_CHANGED:
                    if(GST_MESSAGE_SRC(message) == GST_OBJECT(data.pipeline))
                    {
                        GstState old_state, new_state, pending_state;
                        gst_message_parse_state_changed (message,&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:
                    g_printerr("Unexpected message received!\n");
                    break;
            }
            gst_message_unref(message);
        }
    } while (!terminate);

    gst_object_unref(bus);
    gst_element_set_state(data.pipeline,GST_STATE_NULL);
    gst_object_unref(data.pipeline);
    return 0;
}   


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(gst_pad_is_linked(sink_pad))
    {
        g_print("We are already linked. Ignoring.\n");
        goto exit;
    }

    new_pad_caps = gst_pad_get_current_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;
    }

    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:
    if(new_pad_caps != NULL)
    {
        gst_caps_unref(new_pad_caps);
    }
    gst_object_unref(sink_pad);
}