How to read rtsp stream with gstreamer in C code

Question

Can someone, please, tell me where I can find an example of how to read an rtsp with gstreamer in C?. Actually there are many out there, but I need one where the "rtspsrc" component is explicitly used, all I can find is either "gst-launch" examples or in C code, but using "uridecodebin"

I tried with this, but the "pad_added_handler()" never is called and I don't get any error either

#include <gst/gst.h>

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

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

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

    GstElement *pipeline = gst_pipeline_new ("rtsp-pipeline");
    if (!pipeline) {
        g_printerr ("Pipeline could not be created. Exiting.\n");
        return -1;
    }

    // input
    GstElement *rtspsrc = gst_element_factory_make("rtspsrc", "rtspsrc");
    g_object_set (G_OBJECT (rtspsrc), "location", "rtsp://192.168.1.88:554/11", "latency", 10, NULL);

    // decoding
    GstElement *rtph265depay = gst_element_factory_make("rtph265depay", "rtph265depay");
    GstElement *h265parse = gst_element_factory_make("h265parse", "h265parse");
    GstElement *avdec_h265 = gst_element_factory_make("avdec_h265", "avdec_h265");

    // display
    GstElement *videoconvert = gst_element_factory_make("videoconvert", "videoconvert_screen");
    GstElement *sink = gst_element_factory_make("autovideosink", "nvvideo_renderer");

    gst_bin_add_many(GST_BIN(pipeline), rtph265depay, h265parse, avdec_h265, videoconvert, sink, NULL);
    if (!gst_element_link_many(rtph265depay, h265parse, avdec_h265, videoconvert, sink, NULL)) {
        g_printerr("Elements could not be linked. Exiting.\n");
        return -1;
    }

    // register callback
    g_signal_connect (rtspsrc, "pad-added", G_CALLBACK (pad_added_handler), rtph265depay);


    /* Start playing */
    ret = gst_element_set_state (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 (pipeline);
        return -1;
    }

    /* Listen to the bus */
    bus = gst_element_get_bus (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 (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 (pipeline, GST_STATE_NULL);
  gst_object_unref (pipeline);
  return 0;
}

static void pad_added_handler (GstElement *src, GstPad *new_pad, GstElement *rtphepay) {
    GstPad *sink_pad = gst_element_get_static_pad (rtphepay, "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_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 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);
}

Answer 1

It looks like you followed the "Hello World" example from GStreamer. You are actually doing more than just "Hello World. You want to have callback events triggered. These come from a GLib mainloop.

I would recommend to check out the "Your first application" example from GStreamer instead:

https://gstreamer.freedesktop.org/documentation/application-development/basics/helloworld.html?gi-language=c

Basically you what you want is to add the GLib mainloop and add a bus watch instead to iterating over the bus messages.