GStreamer and SDL

I’m using GStreamer to build a little video player using SDL as video
sink. I would like to render the video on my own window instead of
rendering on the window created by GStreamer, so I could use X overlay
as said in the manual (GStreamer), but it is not what I need. I aim to
add options into sdlvideosink in order to be able to pass SDL_Surface
pointer to the element so that I can create a YUV overlay on my own
window, but I get segfault in SDL_CreateYUVOverlay, despite the
address of pointer is correct. It seems that there is no support for
external threads (created by GStreamer), I mean it is not supposed to
use SDL_Surface in different threads, isn’t ? It works when I call
SDL_CreateYUVOverlay in the same process in which SDL is initialized.
Is this problem related to the threads created by GStreamer ?

Thanks in advance,