How to properly concatenate videos with splitmuxsrc/GStreamer?

I want to concatenate videos using the element splitmuxsrc of gstreamer and put the list of files to be concatenated is passed from C to the splitmuxsrc element through the format-location signal, the same here How to properly concatenate mp4 videos with GStreamer, but not successful yet.

I have been trying:

This works:

$ gst-launch-1.0 -v splitmuxsrc location=path/to/*.mp4 ! decodebin ! videoconvert ! autovideosink

Now, in C/C++: the following does not work.

splitmuxsrc = gst_element_factory_make("splitmuxsrc", "splitmuxsrc");
g_signal_connect (splitmuxsrc, "format-location", G_CALLBACK (format_location_callback), appCtx);

The callback function:

static GStrv *format_location_callback (GstElement * splitmuxsrc, gpointer udata) {
    char ***pppvid = (char***)malloc(1 * sizeof(char**));
    **pppvid = (char**)malloc(2* sizeof(char*));
    for(int i =0 ; i < 2; i++) {
        *pppvid[i] = (char*)malloc(sizeof(char) * 255);
    }
    *pppvid[0] = "path/to/video1";
    *pppvid[1] = "path/to/video1";

    for(int i =0 ; i < 2; i++) {
        g_print("%s\n", *pppvid[i]);
    }
    return pppvid;
}

I expect the pipeline will stream the list of videos (format_location_callback) continuously.

The error:

splitmuxsrc(12181,0x113652600) malloc: *** error for object 0x109146750: pointer being freed was not allocated
splitmuxsrc(12181,0x113652600) malloc: *** set a breakpoint in malloc_error_break to debug
Abort trap: 6

Do someone know how to return a proper list of video paths in the callback function?

I found out that the following callback function works:

static GStrv 
format_location_callback (GstElement * splitmuxsrc, gpointer udata) {
  char **list_of_vids = (char**)malloc(3*sizeof(gchar *));
  list_of_vids[0] = g_build_filename ("", "path/to/vid1", NULL);
  list_of_vids[1] = g_build_filename ("", "path/to/vid2", NULL);

  return list_of_vids;
}