gstreamer pipeline 状态监控, c代码例子

可以提供一个基于GStreamer的状态监控的C代码示例：

#include <gst/gst.h>

static void on_status_changed(GstBus *bus, GstMessage *message, gpointer user_data) {
    GError *error = NULL;
    gchar *debug_info = NULL;
    GstElement *element = GST_ELEMENT(message->src);
    const GstStructure *structure = gst_message_get_structure(message);
    const gchar *status;

    status = gst_structure_get_string(structure, "status");
    gst_message_parse_error(message, &error, &debug_info);

    g_print("Status: %s\n", status);

    if (error != NULL) {
        g_print("Error: %s\n", error->message);
        g_error_free(error);
    }

    if (debug_info != NULL) {
        g_print("Debug info: %s\n", debug_info);
        g_free(debug_info);
    }
}

int main(int argc, char *argv[]) {
    GstElement *pipeline = NULL;
    GstBus *bus = NULL;
    GstCaps *caps = NULL;
    GstStateChangeReturn ret;

    gst_init(&argc, &argv);

    // Create pipeline
    pipeline = gst_pipeline_new("test-pipeline");

    // Add elements to pipeline
    GstElement *src = gst_element_factory_make("videotestsrc", "src");
    GstElement *sink = gst_element_factory_make("autovideosink", "sink");

    gst_bin_add_many(GST_BIN(pipeline), src, sink, NULL);

    // Link elements
    if (!gst_element_link(src, sink)) {
        g_printerr("Failed to link elements\n");
        gst_object_unref(pipeline);
        return -1;
    }

    // Set pipeline to playing state
    ret = gst_element_set_state(pipeline, GST_STATE_PLAYING);
    if (ret == GST_STATE_CHANGE_FAILURE) {
        g_printerr("Failed to set pipeline to playing state\n");
        gst_object_unref(pipeline);
        return -1;
    }

    // Get a bus and connect to the source element's bus
    bus = gst_element_get_bus(pipeline);
    gst_bus_add_watch(bus, on_status_changed, NULL);

    // Run main loop
    GstMessage *message = gst_bus_timed_pop_filtered(bus, GST_CLOCK_TIME_NONE, GST_MESSAGE_ERROR | GST_MESSAGE_EOS);
    if (message != NULL) {
        gst_message_unref(message);
    }

    // Free resources
    gst_object_unref(bus);
    gst_element_set_state(pipeline, GST_STATE_NULL);
    gst_object_unref(pipeline);

    return 0;
}

该示例中，我们创建一个简单的 GStreamer pipeline，由 videotestsrc 元件产生视频数据，再经由 autovideosink 元件输出到屏幕上。我们向 pipeline 的总线(bus)注册了 on_status_changed 回调函数，在该回调函数中，我们可以根据状态信息(status)判断 pipeline 的运行状态，并在发生错误时输出错误信息以及调试信息。