Right? Is this not linked to window size? I could not find any other
meaningful mentions of replay <something> other than the window size:

srtp/srtp.c:1191:   /* initialize replay database */
srtp/srtp.c-1192-   /* window size MUST be at least 64.  MAY be larger.  Values more than
srtp/srtp.c-1193-    * 2^15 aren't meaningful due to how extended sequence numbers are
srtp/srtp.c-1194-    * calculated.   Let a window size of 0 imply the default value. */
srtp/srtp.c-1195-
srtp/srtp.c-1196-   if (p->window_size != 0 && (p->window_size < 64 || p->window_size >= 0x8000))
srtp/srtp.c-1197-     return srtp_err_status_bad_param;