I tried to use some simple ImageEffects (like FishEye, which is normally working without problems on Android devices) together with the QCAR. I understand that QCAR may do some strange things to the graphics buffer internally (if I am right, there is the unity view on top of an camera view), but even then the image effects should work with the Unity scene. I only get a black screen. On the other hand, making a screenshot by calling GetPixels on a Texture2D object works - so, the pixels are in the buffer and ready to be copied...
The problem seems to be that there cannot be a RenderTexture from a QCAR-enabled camera. Is there some way around that? It would be great if I could use the QCAR camera as a RenderTexture.