docs/random/padarch

   1 --src----------------------------       --sink----------------------------
   2                                 |       |
   3                 --srcpad--------|       |--sinkpad-------
   4                 | pad_push()    .       .               |
   5 push()          |  ->chain      .       .  ->chain      | ->    chain()
   6                 |               .       .               |
   7                 ----------------|       |----------------
   8                                 |       |
   9
  10 chain() is the function provided by sink element
  11 sinkpad->chain is a pointer to that function
  12 srcpad->chain should be a copy of that pointer
  13 pad_push() calls the function pointer srcpad->chain
  14 push() is the function provided by the src element