New to gst - need some help:

 what is the best way to pass meta data from one element to the other in gst
   example use case: in a HW accelerated transcoding session, OMX video decoder
   output buffer is sent to OMX video encode. decoder output is present in a
   physically contiguous memory identified by a file descriptor and encode
   needs to use this file descriptor to derive the physical address of
   decoder's output buffer. OMX buffer header provides platform private field
   to carry platform specific data.
   Gst seems to define buffer meta data but what is the best place to embed
   this information. Does gst have any platform private/reserved fields
   (similar to OMX buffer hdr platform private data) to carry such information?
   Another question is how does buffer from one element get passed to another
   element when elements are in different processes? Or gst assume all elements
   run in the same process.this cannot be practical scenario as usually display
       resides in a different process.