Hello Jigneshpatel,
Apparently there is a bug with gdkpixbufoverlay looks like is not supported however i´m going to verify this one, you can make the overlay like this:
gst-launch-1.0 v4l2src device=/dev/video1 num-buffers=300 ! videoconvert ! 'video/x-raw,width=1280,height=720,framerate=(fraction)30/1' ! textoverlay text="Hi There" valignment=top halignment=left font-desc="Sans, 12" ! queue ! x264 ! mp4mux ! filesink location=video.mp4
Regards