On this line it is called new frame is pushed to Streamer github.com/indilib/indi-3rdparty/blob/da...hy/qhy_ccd.cpp#L2596
I think it would be quite straightforward put decodeGPSHeader() before call to Streamer->newFrame(buffer, w * h * bpp / 8 * channels, GPSHeader.start_sec + GPSHeader.start_us / 1000000.0);