OpenGL 3.0+ framebuffer to texture/images

I need a way to capture what is rendered on screen, i have read about glReadPixels but it looks really slow.

Can you suggest a more efficient or just an alternative way for just copying what is rendered by OpenGL 3.0+ to the local RAM and in general to output this in a image or in a data stream?

How i can achieve the same goal with OpenGL ES 2.0 ?

EDIT:

i just forgot: with this OpenGL functions how i can be sure that

• I'm actually reading a complete frame, meaning that there is no overlapping between 2 frames or any nasty side effect


• I'm actually reading the frame that comes right next to the previous one so i do not lose frames