将 Gstrplaybin 链接到自定义视频接收器 videoconvert 和接收器未链接 gstreamer

Question

尝试从管道制作 gstreamer 应用程序：gst-launch-1.0 playbin uri=rtsp://video-sink="videoconvert !video/x-raw,width=720, height=480 !ximagesink"

链接元素出错。发布我的代码：

#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

需要注意的是，playbin 元素提供了从 src 到 sink 的完整管道，因此没有 sink 的管道可以完美运行：

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

接下来是您要创建的正确管道：

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

为了将它嵌入到 GStreamer 应用程序中，不需要链接所有元素。取而代之的是，必要的步骤是构建一个自定义视频输出箱并将其设置为 playbin 的video-sink 属性。换句话说，要走的路是创建一个 bin 并链接必要的元素，然后通过它的 video-sink 属性告诉 playbin 使用它。还需要为 bin 创建一个 GhostPad，并将其指向 bin 内第一个元素的 sink pad。

这是结果：

#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;
}