将 Gstrplaybin 链接到自定义视频接收器 videoconvert 和接收器不链接 gstreamer

Question

Trying to make gstreamer application from the pipeline: gst-launch-1.0 playbin uri=rtsp:// video-sink="videoconvert ! video/x-raw,width=720, height=480 ! ximagesink"

Getting error to link elements. Posting my code:

#include <gst/gst.h>

int main(int argc, char *argv[]) {
    GstElement *source, *videosink, *pipeline, *videoconvert;
    GstCaps *capsFilter;
    GstBus *bus;
    GstMessage *msg;
    GstPad *pad;
    gboolean link_ok;

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


    /* Create Elements */
    pipeline = gst_pipeline_new("my-pipeline");
    source = gst_element_factory_make ("playbin", "source");
    videoconvert = gst_element_factory_make("videoconvert", "convert");
    videosink = gst_element_factory_make("ximagesink", "autovideosink");

    /* set property value */
    g_object_set (source, "uri", "rtsp:<file location>", NULL);

    if (!pipeline || !source || !videoconvert || !videosink)
    {   
            g_printerr ("Not all elements could be created.\n");
            return;
    }   


    gst_bin_add_many (GST_BIN(pipeline), videoconvert, videosink, NULL);
    capsFilter = gst_caps_new_simple("video/x-raw",
                    "width", G_TYPE_INT, 176,
                    "height", G_TYPE_INT, 144, 
                    NULL);
    link_ok = gst_element_link_filtered(videoconvert,videosink, capsFilter);
    gst_caps_unref (capsFilter);

    if (!link_ok) {
            g_warning ("Failed to link element1 and element2!");
    }   
    if (gst_element_link_many( videoconvert, videosink, NULL) != TRUE) {
            g_print ("Failed to link some elements .....1 !\n");
            gst_object_unref (pipeline);
            return -1; 
    }   


      /* Start playing */
    gst_element_set_state (source, GST_STATE_PLAYING);

    /* Wait until error or EOS */
    bus = gst_element_get_bus (source);
    msg = gst_bus_timed_pop_filtered (bus, GST_CLOCK_TIME_NONE,
GST_MESSAGE_ERROR | GST_MESSAGE_EOS);

Answer 1

It should be noted that the playbin element gives a full pipeline from src to sink, so the pipeline without the sink stuff would play perfectly:

gst-launch-1.0 playbin uri=rtsp://127.0.0.1:8551/test

The correct pipeline that you want to create is next:

gst-launch-1.0 playbin uri=rtsp://127.0.0.1:8551/test video-sink="videoconvert ! video/x-raw,width=320,height=240 ! ximagesink"

In order to embed this into GStreamer application, it is not necessary to link all the elements. Instead of that, the necessary steps to make are to build a custom video output bin and set it to playbin's video-sink property. In other words, the way to go is create a bin and link the necessary elements and then tell playbin to use it via it's video-sink property. It is also necessary to create a GhostPad for the bin and point it to the sink pad of the first element within the bin.

This is the result:

#include <gst/gst.h>

int main(int argc, char *argv[]) {
    GstElement *source, *videosink, *pipeline, *videoconvert, *customoutput;
    GstCaps *capsFilter;
    GstBus *bus;
    GstMessage *msg;
    GstPad *pad;
    gboolean add_ok;
    gboolean link_ok;
    GstStateChangeReturn ret;
    GMainLoop *loop;

    /* Initialize GStreamer */
    gst_init (&argc, &argv);
    loop = g_main_loop_new (NULL, FALSE);


    /* Create Elements */
    pipeline = gst_pipeline_new("my-pipeline");
    source = gst_element_factory_make ("playbin", "source");
    videoconvert = gst_element_factory_make("videoconvert", "videoconvert");
    capsFilter = gst_caps_new_simple("video/x-raw",
                    "width", G_TYPE_INT, 320,
                    "height", G_TYPE_INT, 240, 
                    NULL);
    videosink = gst_element_factory_make("ximagesink", "videosink");
    customoutput = gst_bin_new("customoutput");

    // It is possible to create the bin like this 
    // Ghost pads on the bin for unlinked source or sink pads within the bin can automatically be created
    // customoutput =  gst_parse_bin_from_description ("videoconvert ! video/x-raw,width=320 ! ximagesink", TRUE, NULL);
    gst_bin_add_many (GST_BIN (customoutput), videoconvert, videosink, NULL);

    link_ok = gst_element_link_filtered(videoconvert,videosink, capsFilter);
    gst_caps_unref (capsFilter);
    if (!link_ok) {
            g_warning ("Failed to link element1 and element2!");
    }

    GstPad *sinkpad,*ghost_sinkpad;
    sinkpad = gst_element_get_static_pad (videoconvert, "sink"); 
    ghost_sinkpad = gst_ghost_pad_new ("sink", sinkpad); 
    gst_pad_set_active (ghost_sinkpad, TRUE); 
    gst_element_add_pad (customoutput, ghost_sinkpad); 

    /* set property value */
    g_object_set (source, "video-sink", customoutput, NULL);
    g_object_set (source, "uri", "rtsp://127.0.0.1:8551/test", NULL);

    if (!pipeline || !source || !videoconvert || !capsFilter || !videosink || !customoutput)
    {   
            g_printerr ("Not all elements could be created.\n");
            return -1;
    }

    gst_bin_add_many (GST_BIN(pipeline), source,NULL);

    // Start playing */
    ret = gst_element_set_state (pipeline, GST_STATE_PLAYING);
    g_print ("Running...\n");
    g_main_loop_run (loop);
    if (ret == GST_STATE_CHANGE_FAILURE) {
        g_printerr ("Unable to set the pipeline to the playing state.\n");
        gst_object_unref (pipeline);
        return -1;
    }
    /* Wait until error or EOS */
    //bus = gst_element_get_bus (pipeline);
    //msg = gst_bus_timed_pop_filtered (bus, GST_CLOCK_TIME_NONE,GST_MESSAGE_ERROR | GST_MESSAGE_EOS);

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

    return 0;
}