How to add two audio src with pads to the pipeline

General Discussion
1

a pipeline is made to play video/audio files in C++ code.

    /* Create elements */
    pipeline = gst_pipeline_new("mkv-player");
    source = gst_element_factory_make("filesrc", "file-source");
    g_object_set(G_OBJECT(source), "location", "your_file.mkv", NULL);
    decodebin3 = gst_element_factory_make("decodebin3", "decodebin");

    /* Build the pipeline */
    gst_bin_add_many(GST_BIN(pipeline), source, decodebin, NULL);
    gst_element_link(source, decodebin);
    g_signal_connect(decodebin, "pad-added", G_CALLBACK(on_pad_added), NULL);

static void on_pad_added(GstElement *element, GstPad *pad, gpointer data) {
      add video sink bin <======== ok no issues
      //there are two audio srcs with different formats
      //???????? how to add these two audio srcs to the pipeline
      add audio sink bin
}
2

The following pipeline works from command line
gst-launch-1.0 filesrc location=path/file.mkv ! decodebin3 name=demux ! videoconvert ! autovideosink demux.audio_0 ! queue ! audioconvert ! audioresample ! autoaudiosink

video/audio sinks are added explicitly and specifically in the C++ code. The problem is two audio pads come from decodebin3. Not sure how to add them with the same audio sink.

3

there are only two pads from decodebin3 in the diagram of gst-launch-1.0 filesrc location=path/file.mkv ! decodebin3 name=demux ! videoconvert ! autovideosink demux.audio_0 ! queue ! audioconvert ! audioresample ! autoaudiosink

But in C++ code padAdded signal of decodebin3 sends out three pads(one video and two audios).

4

coding error. decodebin3 has only two pads. Problem is solved.