priority thread, since these functions use an internal mutex and may
   delay the thread for up to 100 ms under heavy loads (experienced with
   the mosaic). Instead we now recycle the UDP buffers, which is
   incidentally faster than malloc()/free(). It should avoid "late
   buffer sent" messages. Also removed the --sout-udp-late option because
   "better late than never" (I changed my mind on this).