Depth Buffer Encoding

Hey guys,

is there a way to encode (lossless) the depth buffer using the NvIFR Grid API. I simply tried
to use the GL_DEPTH_ATTACHMENT for data uploading to the Encoder using the following call:

nvIFROGLTransferFramebufferToH264Enc(transferObjectHandle, NULL, fboID, GL_DEPTH_ATTACHMENT, GL_NONE)

I used the GLIFR_SimpleH264 example code to play around that problem. I think the error happends due to the wrong texture format, but i did not realy know. It would be realy great if there is anyone who could help and explain how to encode the buffer using the NvIFR API. Thanks!