2_1.c

//
// Created by daniel on 09/11/2019.
//
#include <gst/gst.h>

typedef struct _CustomData {
    GstElement *pipeline;
    GstElement *v4l2src;
    GstElement *caps_filter1;
    GstElement *decodebin;
    GstElement *ximagesrc;
    GstElement *caps_filter3;
    GstElement *videoscale;
    GstElement *caps_filter4;
    GstElement *alpha;
    GstElement *videobox;
    GstElement *videotestsrc;
    GstElement *caps_filter2;
    GstElement *videomixer;
    GstElement *videoconvert;
    GstElement *xvimagesink;
} CustomData;

#define BALL_PATTERN 18

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

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

    GstCaps *caps;
    GstPad *mixerpad_1, *mixerpad_2, *mixerpad_3;
    GstPad *videotestsrc_pad, *videobox_pad;

    // initialize
    gst_init(&argc, &argv);

    // create elements
    data.v4l2src = gst_element_factory_make("v4l2src", NULL);
    data.caps_filter1 = gst_element_factory_make("capsfilter", "caps_filter1");
    data.decodebin = gst_element_factory_make("decodebin", NULL);
    data.ximagesrc = gst_element_factory_make("ximagesrc", NULL);
    data.caps_filter3 = gst_element_factory_make("capsfilter", "caps_filter3");
    data.videoscale = gst_element_factory_make("videoscale", NULL);
    data.caps_filter4 = gst_element_factory_make("capsfilter", "caps_filter4");
    data.alpha = gst_element_factory_make("alpha", NULL);
    data.videobox = gst_element_factory_make("videobox", NULL);
    data.videotestsrc = gst_element_factory_make("videotestsrc", NULL);
    data.caps_filter2 = gst_element_factory_make("capsfilter", "caps_filter2");
    data.videomixer = gst_element_factory_make("videomixer", "mix");
    data.videoconvert = gst_element_factory_make("videoconvert", NULL);
    data.xvimagesink = gst_element_factory_make("xvimagesink", NULL);

    // set element properties
    g_object_set(data.xvimagesink, "sync", FALSE, NULL);
    g_object_set(data.v4l2src, "device", "/dev/video0", NULL);
    g_object_set(data.videotestsrc, "pattern", BALL_PATTERN, NULL);
    g_object_set(data.ximagesrc, "startx", 0, NULL);
    g_object_set(data.ximagesrc, "use-damage", 0, NULL);
    g_object_set(data.videoscale, "method", 0, NULL);
    g_object_set(data.alpha, "alpha", 1.0, NULL);
    g_object_set(data.videobox, "border-alpha", 0.0, NULL);
    g_object_set(data.videobox, "top", -600, NULL);
    g_object_set(data.videobox, "left", -1280, NULL);

    // set appropriate caps
    caps = gst_caps_new_simple("image/jpeg",
                               "framerate", GST_TYPE_FRACTION, 30, 1,
                               "width", G_TYPE_INT, 640,
                               "height", G_TYPE_INT, 480,
                               NULL);
    g_object_set(data.caps_filter1, "caps", caps, NULL);

    caps = gst_caps_new_simple("video/x-raw",
                               "framerate", GST_TYPE_FRACTION, 30, 1,
                               "width", G_TYPE_INT, 1920,
                               "height", G_TYPE_INT, 1080,
                               NULL);
    g_object_set(data.caps_filter2, "caps", caps, NULL);

    caps = gst_caps_new_simple("video/x-raw",
                               "framerate", GST_TYPE_FRACTION, 30, 1,
                               NULL);
    g_object_set(data.caps_filter3, "caps", caps, NULL);
    caps = gst_caps_new_simple("video/x-raw",
                               "width", G_TYPE_INT, 640,
                               "height", G_TYPE_INT, 480,
                               NULL);
    g_object_set(data.caps_filter4, "caps", caps, NULL);


    data.pipeline = gst_pipeline_new("pipeline");
    if (!data.v4l2src || !data.decodebin || !data.ximagesrc || !data.videoscale || !data.alpha || !data.videobox ||
        !data.videotestsrc || !data.videomixer || !data.videoconvert || !data.xvimagesink || !data.caps_filter1 ||
        !data.caps_filter2 ||
        !data.caps_filter3 || !data.caps_filter4) {
        g_printerr("Not all element could be created\n");
        return -1;
    }

    gst_bin_add_many(GST_BIN(data.pipeline),
                     data.v4l2src,
                     data.caps_filter1,
                     data.decodebin,
                     data.ximagesrc,
                     data.caps_filter3,
                     data.videoscale,
                     data.caps_filter4,
                     data.alpha,
                     data.videobox,
                     data.videotestsrc,
                     data.caps_filter2,
                     data.videomixer,
                     data.videoconvert,
                     data.xvimagesink,
                     NULL);

    if (
            !gst_element_link_many(data.videomixer, data.videoconvert, data.xvimagesink, NULL) ||
            !gst_element_link_many(data.v4l2src, data.caps_filter1, data.decodebin, NULL) ||
            !gst_element_link_many(data.videotestsrc, data.caps_filter2, NULL) ||
            !gst_element_link_many(data.ximagesrc, data.caps_filter3, data.videoscale, data.caps_filter4, data.alpha,
                                   data.videobox, NULL)
            ) {
        g_printerr("Elements could not be linked.\n");
        gst_object_unref(data.pipeline);
        return -1;
    }

    // link on-request pads
    // this one for decodebin
    // NOTE: linking of decodebin pad should be done in callback

    // this one for videotestsrc
    mixerpad_2 = gst_element_get_request_pad(data.videomixer, "sink_%u");
    videotestsrc_pad = gst_element_get_static_pad(data.caps_filter2, "src");
    if (gst_pad_link(videotestsrc_pad, mixerpad_2) != GST_PAD_LINK_OK) {
        g_printerr("Videotestsrc pad could not be linked\n");
        g_object_unref(data.pipeline);
        return -1;
    }

    // this one for videobox
    mixerpad_3 = gst_element_get_request_pad(data.videomixer, "sink_%u");
    videobox_pad = gst_element_get_static_pad(data.videobox, "src");
    if (gst_pad_link(videobox_pad, mixerpad_3) != GST_PAD_LINK_OK) {
        g_printerr("Videobox pad could not be linked\n");
        g_object_unref(data.pipeline);
        return -1;
    }

    // connect to the pad-added signal
    g_signal_connect(data.decodebin, "pad-added", G_CALLBACK(decodebin_pad_added), &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;
}

static void decodebin_pad_added(GstElement *src, GstPad *new_pad, CustomData *data) {
    GstPad *mixer_pad = gst_element_get_request_pad(data->videomixer, "sink_%u");

    GstPadLinkReturn ret;
    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(new_pad)) {
        g_print("Pad is already linked - ignoring\n");
        goto exit;
    }

    ret = gst_pad_link(new_pad, mixer_pad);
    if (GST_PAD_LINK_FAILED(ret)) {
        g_print("Type is %s, but link has failed.\n", new_pad_type);
        goto exit;
    } else {
        g_print("Link has been successful (type '%s').\n", new_pad_type);
    }

    exit:
    /* Unreference the sink pad */
    gst_object_unref(mixer_pad);

}