gstreamer application crash with signal 11

Question

I am working on Gstreamer 1.14.05 on an embedded piece of hardware. I have done up a function (callback) that will name the new record file according to the a fixed recording duration specified - YYMMDD_HHMMSS(start)_HHMMSS(end).mp4(see code)

I have runned the code and I have gotten problem that I believed is related to segmentation fault and I believe somehow it has got to do with this naming

The actual error:

audit: type=1701 audit(1648454527.720:4): auid=4294967295 uid=0 gid=0 ses=4294967295 pid=3032 comm="queue0:src" exe="/home/root/videoTest" sig=11 res=1 

Segmentation fault (core dumped) 

The segfault happens rather in a haphazard manner, soometimes it happened at the 1st 1-2 intervals (within 60sec). Other times it may take up to 6 mins.

Code:

// helper code to rename file in specified format
using time_pt = std::chrono::system_clock::time_point;
std::string replaceStr(const time_pt& t1,
                       const time_pt& t2,
                       const std::string& dir)
{
    const std::string format1 = "%Y%m%d_%H%M%S";
    const std::string format2 = "%H%M%S";
    std::time_t tt1 = std::chrono::system_clock::to_time_t(t1);

    std::tm tm = *std::localtime(&tt1);
    std::stringstream ss;
    ss << dir << "/";
    ss << std::put_time( &tm, format1.c_str() );

    std::time_t tt2 = std::chrono::system_clock::to_time_t(t2);
    tm = *std::localtime(&tt2); //Locale time-zone, usually UTC by default.

    ss << "_" << std::put_time( &tm, format2.c_str() ) << ".mp4";

    return ss.str();
}

// function to name the video file
gchararray
format_location_callback(GstElement * splitmux,
                         guint fragment_id,
                         gpointer udata)
{  
    // R is a structure for recording data
    // this function is called every 30s
    R* rec          = (R*)  udata; 

    time_pt start  = std::chrono::system_clock::now();
    time_pt end    = start + std::chrono::seconds(30);

    rec->last_start      = start;
    rec->last_split      = replaceStr(start, end, "/media/video");
    
    return (rec->last_split).c_str();
}

// the code to install this callback
g_signal_connect (splitmuxsink, "format-location",
                                 (GCallback)format_location_callback,
                                  &rec);

Would appreciate on how else could I proceed to debug on the code and find the error or if you could point out whether the replaceStr function is efficient and bug free

Thanks