Correspondence between appsrc input and appsink output buffers

[benjamin.hepp at posteo.de]

Hi everyone,

I'm new to gstreamer (it's great!) so I very much appreciate any help.

I basically have the following setup:
Custom video-source -> appsrc -> encoding -> appsink -> send over 
network together with other information that corresponds to each frame 
(e.g. GPS).
On the server I receive buffer and associated information -> appsrc -> 
decoding -> appsink.

Now in both cases I push a buffer into an appsrc that has some 
associated information. Is there any way to link this information again 
to a buffer coming out of the appsink?

I now that theoretically there is no guarantee that one buffer out of 
the appsink is one frame, but in my case it is. So on the client side I 
can just assume that no frame is ever dropped (assuming I never hit any 
buffer limit).
However, on the receiving side the decoder sometimes needs to drop some 
frame until it can start decoding and I don't know how many it drops. So 
I'm in the situation that I cannot link the information to the buffers 
coming out of the appsink.
Unfortunately I can't use the buffer offset or PTS information because 
this is just reset by the encoder/decoder.

Is there any other way to establish these correspondences?

Cheers
Benjamin