DMA to VideoChannel

I have application creating video channel. Video channel allocates a offscreen buffer into VGA memory for overlaying with video data.Does anybody know how to obtain the physical address, in order to setup DMA transfer from grabber.
Thanks in forward!

Let me put the question that way:
How to convert virtual memory address of shared object - the offscreen buffer
into physical address???

In the online help search for DMA.

Thanks Mario,
I got it!