send the image buffer on decklink HD Extreame 3d+ card using GlReadPixel

when we send the image buffer on decklink HD Extreame 3d+ card using GlReadPixel
then SDI output generate flickering,This NVidia Card generate More than 100 fps but Decklink card take only 25 fps,how to send the frames on decklink card without flickring,
I am sending my code file please check it and send me ur valuable suggestion

Regards
anurag