GStreamer:如何连接动态垫 [英] GStreamer: how to connect dynamic pads

问题描述

我正在尝试使用 GStreamer 播放文件中的 MP4 视频.我设法使用 playbin2 并从命令提示符使用以下命令播放文件:

I'm trying to use GStreamer to play MP4 video from a file. I have managed to play the file using playbin2 and from the command prompt using:

gst-launch filesrc location=bbb.mp4 ! decodebin2 ! autovideosink

我预计将来我将需要创建更复杂的管道，因此我试图对管道进行编程".在我的程序中，我试图复制上面的管道，但是我有一个问题，我怀疑与将 decodebin2 的动态或有时"源焊盘连接到自动视频接收器有关.我使用这些元素只是为了让事情尽可能简单.

I am expecting in the future that I will need to create more complicated pipelines and hence why I'm attempting to 'program' the pipeline. In my program I am attempting to replicate the pipeline above, however I have an issue which I suspect is related to connecting the dynamic or "sometimes" source pad of decodebin2 to the autovideo sink. I am using these elements only to keep things as simple as possible.

static void on_new_decoded_pad(GstElement* object,
                           GstPad* arg0,
                           gboolean arg1,
                           gpointer user_data)
{
    // dynamically connect decoderbin2 src pad to autovideosink sink pad
}

static gboolean bus_call (GstBus *bus, GstMessage *msg, gpointer data)
{
    // handle bus messages
}

int main(int argc, char *argv[])
{
    GMainLoop *loop;
    GstElement *pipeline, *source, *decodebin, *videosink;
    GstBus *bus;

    gst_init (&argc, &argv);
    loop = g_main_loop_new (NULL, FALSE);

    pipeline  = gst_pipeline_new ("pipeline");
    source    = gst_element_factory_make("filesrc",       "source");
    decodebin = gst_element_factory_make("decodebin2",    "decodebin");
    videosink = gst_element_factory_make("autovideosink", "videosink");

    /* check elements were created successfully */
    if (!pipeline || !source || !decodebin || !videosink) {
        // Failed to create element. Exit Program
        return -1;
    }

    /* apply properties to elements before adding to pipeline */
    gchar * filename = "bbb.mp4";
    g_object_set(G_OBJECT(source), "location", filename, NULL);

    /* add a message handler */
    bus = gst_pipeline_get_bus (GST_PIPELINE (pipeline));
    gst_bus_add_watch (bus, bus_call, loop);
    gst_object_unref (bus);

    /* add elements to pipeline (and bin if necessary) before linking them */
    gst_bin_add_many(GST_BIN (pipeline),
                     source,
                     decodebin,
                     videosink,
                     NULL);

    gst_element_link_pads(source, "src", decodebin, "sink");

    /* decodebins src pad is a sometimes pad - it gets created dynamically */
    g_signal_connect(decodebin, "new-decoded-pad", G_CALLBACK(on_new_decoded_pad),   videosink);

    /* run pipeline */
    gst_element_set_state(GST_ELEMENT(pipeline), GST_STATE_PLAYING);

    g_main_loop_run(loop);

    gst_element_set_state(GST_ELEMENT(pipeline), GST_STATE_NULL);
    gst_object_unref (pipeline);

    return 0;
}

当我运行这个程序时，我期望通过回调函数调用 on_new_decoded_pa​​d，该函数在行中设置:

What I expect to happen when I run this program, is for the on_new_decoded_pad to get called via a call back function, which is set in the line:

g_signal_connect(decodebin, "new-decoded-pad", G_CALLBACK(on_new_decoded_pad), videosink);

并允许我适当地连接焊盘.但它永远不会被调用.事实上，程序似乎完全通过然后就退出了(主循环什么也不做).

and would allow me to connect the pads appropriately. But it never gets called. In fact the program seems to pass through entirely and then just exit (the main loop does nothing).

如果有人能指出我在回调方面做错了什么，或者解释还需要做什么才能使本示例使用提供的元素播放 mp4，我将不胜感激.

I'd really appreciate it if someone could point out what I've done wrong with regards to the callback or explain what else needs to be done in order for this example to play mp4 using the provided elements.

问候.

推荐答案

on_new_decoded_pa​​d is depreciated 使用pad- added"代替.

on_new_decoded_pad is depreciated use "pad-added" instead.

我仍然有一个与 decodebin2 相关的问题，您可以在这里找到:GStreamer 强制 decodebin2 输出类型

I still have an issue relating to decodebin2 which you can find here: GStreamer force decodebin2 output type

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