rtp.c

/*
 * Apple RTP protocol handler. This file is part of Shairport.
 * Copyright (c) James Laird 2013
 * Copyright (c) Mike Brady 2014 -- 2018
 * All rights reserved.
 *
 * Permission is hereby granted, free of charge, to any person
 * obtaining a copy of this software and associated documentation
 * files (the "Software"), to deal in the Software without
 * restriction, including without limitation the rights to use,
 * copy, modify, merge, publish, distribute, sublicense, and/or
 * sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
 * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
 * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 * OTHER DEALINGS IN THE SOFTWARE.
 */

#include "rtp.h"
#include "common.h"
#include "player.h"
#include "rtsp.h"
#include <arpa/inet.h>
#include <errno.h>
#include <fcntl.h>
#include <inttypes.h>
#include <math.h>
#include <memory.h>
#include <netdb.h>
#include <netinet/in.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <time.h>
#include <unistd.h>

uint64_t local_to_remote_time_jitters;
uint64_t local_to_remote_time_jitters_count;

void rtp_initialise(rtsp_conn_info *conn) {
  conn->rtp_time_of_last_resend_request_error_fp = 0;
  conn->rtp_running = 0;
  // initialise the timer mutex
  int rc = pthread_mutex_init(&conn->reference_time_mutex, NULL);
  if (rc)
    debug(1, "Error initialising reference_time_mutex.");
}

void rtp_terminate(rtsp_conn_info *conn) {

  // destroy the timer mutex
  int rc = pthread_mutex_destroy(&conn->reference_time_mutex);
  if (rc)
    debug(1, "Error destroying reference_time_mutex variable.");
}

void rtp_audio_receiver_cleanup_handler(void *arg) {
  debug(3, "Audio Receiver Cleanup.");
  rtsp_conn_info *conn = (rtsp_conn_info *)arg;
  debug(1,"shutdown audio socket.");
  shutdown(conn->audio_socket,SHUT_RDWR);  
  debug(1,"close audio socket.");
  close(conn->audio_socket);
  debug(3, "Audio Receiver Cleanup Successful.");
}

void *rtp_audio_receiver(void *arg) {
  pthread_cleanup_push(rtp_audio_receiver_cleanup_handler, arg);
  rtsp_conn_info *conn = (rtsp_conn_info *)arg;

  int32_t last_seqno = -1;
  uint8_t packet[2048], *pktp;

  uint64_t time_of_previous_packet_fp = 0;
  float longest_packet_time_interval_us = 0.0;

  // mean and variance calculations from "online_variance" algorithm at
  // https://en.wikipedia.org/wiki/Algorithms_for_calculating_variance#Online_algorithm

  int32_t stat_n = 0;
  float stat_mean = 0.0;
  float stat_M2 = 0.0;

  ssize_t nread;
  while (1) {
    nread = recv(conn->audio_socket, packet, sizeof(packet), 0);

    uint64_t local_time_now_fp = get_absolute_time_in_fp();
    if (time_of_previous_packet_fp) {
      float time_interval_us =
          (((local_time_now_fp - time_of_previous_packet_fp) * 1000000) >> 32) * 1.0;
      time_of_previous_packet_fp = local_time_now_fp;
      if (time_interval_us > longest_packet_time_interval_us)
        longest_packet_time_interval_us = time_interval_us;
      stat_n += 1;
      float stat_delta = time_interval_us - stat_mean;
      stat_mean += stat_delta / stat_n;
      stat_M2 += stat_delta * (time_interval_us - stat_mean);
      if (stat_n % 2500 == 0) {
        debug(2, "Packet reception interval stats: mean, standard deviation and max for the last "
                 "2,500 packets in microseconds: %10.1f, %10.1f, %10.1f.",
              stat_mean, sqrtf(stat_M2 / (stat_n - 1)), longest_packet_time_interval_us);
        stat_n = 0;
        stat_mean = 0.0;
        stat_M2 = 0.0;
        time_of_previous_packet_fp = 0;
        longest_packet_time_interval_us = 0.0;
      }
    } else {
      time_of_previous_packet_fp = local_time_now_fp;
    }

    if (nread >= 0) {
      ssize_t plen = nread;
      uint8_t type = packet[1] & ~0x80;
      if (type == 0x60 || type == 0x56) { // audio data / resend
        pktp = packet;
        if (type == 0x56) {
          pktp += 4;
          plen -= 4;
        }
        seq_t seqno = ntohs(*(uint16_t *)(pktp + 2));
        // increment last_seqno and see if it's the same as the incoming seqno

        if (type == 0x60) { // regular audio data
          if (last_seqno == -1)
            last_seqno = seqno;
          else {
            last_seqno = (last_seqno + 1) & 0xffff;
            // if (seqno != last_seqno)
            //  debug(3, "RTP: Packets out of sequence: expected: %d, got %d.", last_seqno, seqno);
            last_seqno = seqno; // reset warning...
          }
        } else {
          debug(3, "Audio Receiver -- Retransmitted Audio Data Packet %u received.", seqno);
        }

        uint32_t actual_timestamp = ntohl(*(uint32_t *)(pktp + 4));
        int64_t timestamp = monotonic_timestamp(actual_timestamp, conn);

        // if (packet[1]&0x10)
        //	debug(1,"Audio packet Extension bit set.");

        pktp += 12;
        plen -= 12;

        // check if packet contains enough content to be reasonable
        if (plen >= 16) {
          if ((config.diagnostic_drop_packet_fraction == 0.0) ||
              (drand48() > config.diagnostic_drop_packet_fraction))
            player_put_packet(seqno, actual_timestamp, timestamp, pktp, plen, conn);
          else
            debug(3, "Dropping audio packet %u to simulate a bad connection.", seqno);
          continue;
        }
        if (type == 0x56 && seqno == 0) {
          debug(2, "resend-related request packet received, ignoring.");
          continue;
        }
        debug(1, "Audio receiver -- Unknown RTP packet of type 0x%02X length %d seqno %d", type,
              nread, seqno);
      }
      warn("Audio receiver -- Unknown RTP packet of type 0x%02X length %d.", type, nread);
    } else {
      debug(1, "Error receiving an audio packet.");
    }
  }

  /*
  debug(3, "Audio receiver -- Server RTP thread interrupted. terminating.");
  close(conn->audio_socket);
  */

  debug(1, "Audio receiver thread \"normal\" exit -- this can't happen. Hah!");
  pthread_cleanup_pop(0); // don't execute anything here.
  debug(2, "Audio receiver thread exit.");
  pthread_exit(NULL);
}

void rtp_control_handler_cleanup_handler(void *arg) {
  debug(3, "Control Receiver Cleanup.");
  rtsp_conn_info *conn = (rtsp_conn_info *)arg;
  debug(1,"shutdown control socket.");
  shutdown(conn->control_socket,SHUT_RDWR);  
  debug(1,"close control socket.");
  close(conn->control_socket);
  debug(3, "Control Receiver Cleanup Successful.");
}

void *rtp_control_receiver(void *arg) {
  pthread_cleanup_push(rtp_control_handler_cleanup_handler, arg);
  rtsp_conn_info *conn = (rtsp_conn_info *)arg;

  conn->reference_timestamp = 0; // nothing valid received yet
  uint8_t packet[2048], *pktp;
  // struct timespec tn;
  uint64_t remote_time_of_sync;
  int64_t sync_rtp_timestamp;
  ssize_t nread;
  while (1) {
    nread = recv(conn->control_socket, packet, sizeof(packet), 0);
    // local_time_now = get_absolute_time_in_fp();
    //        clock_gettime(CLOCK_MONOTONIC,&tn);
    //        local_time_now=((uint64_t)tn.tv_sec<<32)+((uint64_t)tn.tv_nsec<<32)/1000000000;

    if (nread >= 0) {

      if ((config.diagnostic_drop_packet_fraction == 0.0) ||
          (drand48() > config.diagnostic_drop_packet_fraction)) {

        ssize_t plen = nread;
        if (packet[1] == 0xd4) {                       // sync data
                                                       /*
                                                            // the following stanza is for debugging only -- normally commented out.
                                                            {
                                                              char obf[4096];
                                                              char *obfp = obf;
                                                              int obfc;
                                                              for (obfc = 0; obfc < plen; obfc++) {
                                                                snprintf(obfp, 3, "%02X", packet[obfc]);
                                                                obfp += 2;
                                                              };
                                                              *obfp = 0;
                                             
                                             
                                                              // get raw timestamp information
                                                              // I think that a good way to understand these timestamps is that
                                                              // (1) the rtlt below is the timestamp of the frame that should be playing at the
                                                              // client-time specified in the packet if there was no delay
                                                              // and (2) that the rt below is the timestamp of the frame that should be playing
                                                              // at the client-time specified in the packet on this device taking account of
                                                              // the delay
                                                              // Thus, (3) the latency can be calculated by subtracting the second from the
                                                              // first.
                                                              // There must be more to it -- there something missing.
                                             
                                                              // In addition, it seems that if the value of the short represented by the second
                                                              // pair of bytes in the packe is 7
                                                              // then an extra time lag is expected to be added, presumably by
                                                              // the AirPort Express.
                                             
                                                              // Best guess is that this delay is 11,025 frames.
                                             
                                                              // uint32_t rtlt = nctohl(&packet[4]); // raw timestamp less latency
                                                              // uint32_t rt = nctohl(&packet[16]);  // raw timestamp
                                             
                                                              // uint32_t fl = nctohs(&packet[2]); //
                                             
                                                              // debug(1,"Sync Packet of %d bytes received: \"%s\", flags: %d, timestamps %u and
                                                         %u,
                                                         giving a latency of %d frames.",plen,obf,fl,rt,rtlt,rt-rtlt);
                                                              // debug(1,"Monotonic timestamps are: %" PRId64 " and %" PRId64 "
                                                         respectively.",monotonic_timestamp(rt, conn),monotonic_timestamp(rtlt, conn));
                                                            }
                                                       */
          if (conn->local_to_remote_time_difference) { // need a time packet to be interchanged
                                                       // first...

            remote_time_of_sync = (uint64_t)nctohl(&packet[8]) << 32;
            remote_time_of_sync += nctohl(&packet[12]);

            // debug(1,"Remote Sync Time: %0llx.",remote_time_of_sync);

            sync_rtp_timestamp = monotonic_timestamp(nctohl(&packet[16]), conn);
            int64_t rtp_timestamp_less_latency = monotonic_timestamp(nctohl(&packet[4]), conn);

            // debug(1,"Sync timestamp is %u.",ntohl(*((uint32_t *)&packet[16])));

            if (config.userSuppliedLatency) {
              if (config.userSuppliedLatency != conn->latency) {
                debug(1, "Using the user-supplied latency: %" PRId64 ".",
                      config.userSuppliedLatency);
              }
              conn->latency = config.userSuppliedLatency;
            } else {

              // It seems that the second pair of bytes in the packet indicate whether a fixed
              // delay of 11,025 frames should be added -- iTunes set this field to 7 and
              // AirPlay sets it to 4.

              // However, on older versions of AirPlay, the 11,025 frames seem to be necessary too

              // The value of 11,025 (0.25 seconds) is a guess based on the "Audio-Latency"
              // parameter
              // returned by an AE.

              // Sigh, it would be nice to have a published protocol...

              uint16_t flags = nctohs(&packet[2]);
              int64_t la = sync_rtp_timestamp - rtp_timestamp_less_latency;
              // debug(3, "Latency derived just from the sync packet is %" PRId64 " frames.", la);
              if ((flags == 7) || ((conn->AirPlayVersion > 0) && (conn->AirPlayVersion <= 353)) || ((conn->AirPlayVersion > 0) && (conn->AirPlayVersion >= 371))) {
                la += config.fixedLatencyOffset;
                // debug(3, "A fixed latency offset of %d frames has been added, giving a latency of
                // "
                //         "%" PRId64
                //         " frames with flags: %d and AirPlay version %d (triggers if 353 or
                //         less).",
                //      config.fixedLatencyOffset, la, flags, conn->AirPlayVersion);
              }
              if ((conn->maximum_latency) && (conn->maximum_latency < la))
                la = conn->maximum_latency;
              if ((conn->minimum_latency) && (conn->minimum_latency > la))
                la = conn->minimum_latency;

              const int max_frames = ((3 * BUFFER_FRAMES * 352) / 4) - 11025;

              if ((la < 0) || (la > max_frames)) {
                warn("An out-of-range latency request of %" PRId64
                     " frames was ignored. Must be %d frames or less (44,100 frames per second). "
                     "Latency remains at %" PRId64 " frames.",
                     la, max_frames, conn->latency);
              } else {

                if (la != conn->latency) {
                  conn->latency = la;
                  debug(3, "New latency detected: %" PRId64 ", sync latency: %" PRId64
                           ", minimum latency: %" PRId64 ", maximum "
                           "latency: %" PRId64 ", fixed offset: %" PRId64 ".",
                        la, sync_rtp_timestamp - rtp_timestamp_less_latency, conn->minimum_latency,
                        conn->maximum_latency, config.fixedLatencyOffset);
                }
              }
            }

            debug_mutex_lock(&conn->reference_time_mutex, 1000, 1);

            // this is for debugging
            // uint64_t old_remote_reference_time = conn->remote_reference_timestamp_time;
            // int64_t old_reference_timestamp = conn->reference_timestamp;
            // int64_t old_latency_delayed_timestamp = conn->latency_delayed_timestamp;
            conn->remote_reference_timestamp_time = remote_time_of_sync;
            conn->reference_timestamp_time =
                remote_time_of_sync - conn->local_to_remote_time_difference;
            conn->reference_timestamp = sync_rtp_timestamp;
            conn->latency_delayed_timestamp = rtp_timestamp_less_latency;
            debug_mutex_unlock(&conn->reference_time_mutex, 3);

            // this is for debugging
            /*
            uint64_t time_difference = remote_time_of_sync - old_remote_reference_time;
            int64_t reference_frame_difference = sync_rtp_timestamp - old_reference_timestamp;
            int64_t delayed_frame_difference = rtp_timestamp_less_latency -
            old_latency_delayed_timestamp;

            if (old_remote_reference_time)
              debug(1,"Time difference: %" PRIu64 " reference and delayed frame differences: %"
            PRId64 "
            and %" PRId64 ", giving rates of %f and %f respectively.",
                (time_difference*1000000)>>32,reference_frame_difference,delayed_frame_difference,(1.0*(reference_frame_difference*10000000))/((time_difference*10000000)>>32),(1.0*(delayed_frame_difference*10000000))/((time_difference*10000000)>>32));
            else
              debug(1,"First sync received");
            */

            // debug(1,"New Reference timestamp and timestamp time...");
            // get estimated remote time now
            // remote_time_now = local_time_now + local_to_remote_time_difference;

            // debug(1,"Sync Time is %lld us late (remote
            // times).",((remote_time_now-remote_time_of_sync)*1000000)>>32);
            // debug(1,"Sync Time is %lld us late (local
            // times).",((local_time_now-reference_timestamp_time)*1000000)>>32);
          } else {
            debug(2, "Sync packet received before we got a timing packet back.");
          }
        } else if (packet[1] == 0xd6) { // resent audio data in the control path -- whaale only?
          pktp = packet + 4;
          plen -= 4;
          seq_t seqno = ntohs(*(uint16_t *)(pktp + 2));
          debug(3, "Control Receiver -- Retransmitted Audio Data Packet %u received.", seqno);

          uint32_t actual_timestamp = ntohl(*(uint32_t *)(pktp + 4));
          int64_t timestamp = monotonic_timestamp(actual_timestamp, conn);

          pktp += 12;
          plen -= 12;

          // check if packet contains enough content to be reasonable
          if (plen >= 16) {
            player_put_packet(seqno, actual_timestamp, timestamp, pktp, plen, conn);
            continue;
          } else {
            debug(3, "Too-short retransmitted audio packet received in control port, ignored.");
          }
        } else
          debug(1, "Control Receiver -- Unknown RTP packet of type 0x%02X length %d, ignored.",
                packet[1], nread);
      } else {
        debug(3, "Control Receiver -- dropping a packet to simulate a bad network.");
      }
    } else {
      debug(1, "Control Receiver -- error receiving a packet.");
    }
  }
  debug(1, "Control RTP thread \"normal\" exit -- this can't happen. Hah!");
  pthread_cleanup_pop(0); // don't execute anything here.
  debug(2, "Control RTP thread exit.");
  pthread_exit(NULL);
}

void *rtp_timing_sender(void *arg) {
  rtsp_conn_info *conn = (rtsp_conn_info *)arg;
  struct timing_request {
    char leader;
    char type;
    uint16_t seqno;
    uint32_t filler;
    uint64_t origin, receive, transmit;
  };

  uint64_t request_number = 0;

  struct timing_request req; // *not* a standard RTCP NACK

  req.leader = 0x80;
  req.type = 0xd2; // Timing request
  req.filler = 0;
  req.seqno = htons(7);

  conn->time_ping_count = 0;
  while (1) {
    // debug(1,"Send a timing request");

    if (!conn->rtp_running)
      debug(1, "rtp_timing_sender called without active stream in RTSP conversation thread %d!",
            conn->connection_number);

    // debug(1, "Requesting ntp timestamp exchange.");

    req.filler = 0;
    req.origin = req.receive = req.transmit = 0;

    //    clock_gettime(CLOCK_MONOTONIC,&dtt);
    conn->departure_time = get_absolute_time_in_fp();
    socklen_t msgsize = sizeof(struct sockaddr_in);
#ifdef AF_INET6
    if (conn->rtp_client_timing_socket.SAFAMILY == AF_INET6) {
      msgsize = sizeof(struct sockaddr_in6);
    }
#endif
    if ((config.diagnostic_drop_packet_fraction == 0.0) ||
        (drand48() > config.diagnostic_drop_packet_fraction)) {
      if (sendto(conn->timing_socket, &req, sizeof(req), 0,
                 (struct sockaddr *)&conn->rtp_client_timing_socket, msgsize) == -1) {
        char em[1024];
        strerror_r(errno, em, sizeof(em));
        debug(1, "Error %d using send-to to the timing socket: \"%s\".", errno, em);
      }
    } else {
      debug(3, "Timing Sender Thread -- dropping outgoing packet to simulate bad network.");
    }

    request_number++;

    if (request_number <= 4)
      usleep(500000); // these are thread cancellation points
    else
      usleep(3000000);
  }
  debug(3, "rtp_timing_sender thread interrupted. This should never happen.");
  pthread_exit(NULL);
}

void rtp_timing_receiver_cleanup_handler(void *arg) {
  debug(3, "Timing Receiver Cleanup.");
  rtsp_conn_info *conn = (rtsp_conn_info *)arg;
  pthread_cancel(conn->timer_requester);
  pthread_join(conn->timer_requester, NULL);
  debug(1,"shutdown timing socket.");
  shutdown(conn->timing_socket,SHUT_RDWR);  
  debug(1,"close timing socket.");
  close(conn->timing_socket);
  debug(3, "Timing Receiver Cleanup Successful.");
}

void *rtp_timing_receiver(void *arg) {
  pthread_cleanup_push(rtp_timing_receiver_cleanup_handler, arg);
  rtsp_conn_info *conn = (rtsp_conn_info *)arg;

  uint8_t packet[2048];
  ssize_t nread;
  pthread_create(&conn->timer_requester, NULL, &rtp_timing_sender, arg);
  //    struct timespec att;
  uint64_t distant_receive_time, distant_transmit_time, arrival_time, return_time;
  local_to_remote_time_jitters = 0;
  local_to_remote_time_jitters_count = 0;
  // uint64_t first_remote_time = 0;
  uint64_t first_local_time = 0;

  uint64_t first_local_to_remote_time_difference = 0;
  // uint64_t first_local_to_remote_time_difference_time;
  // uint64_t l2rtd = 0;
  while (1) {
    nread = recv(conn->timing_socket, packet, sizeof(packet), 0);

    if (nread >= 0) {

      if ((config.diagnostic_drop_packet_fraction == 0.0) ||
          (drand48() > config.diagnostic_drop_packet_fraction)) {
        arrival_time = get_absolute_time_in_fp();

        // ssize_t plen = nread;
        // debug(1,"Packet Received on Timing Port.");
        if (packet[1] == 0xd3) { // timing reply
          /*
          char obf[4096];
          char *obfp = obf;
          int obfc;
          for (obfc=0;obfc<plen;obfc++) {
            snprintf(obfp, 3, "%02X", packet[obfc]);
            obfp+=2;
          };
          *obfp=0;
          //debug(1,"Timing Packet Received: \"%s\"",obf);
          */

          // arrival_time = ((uint64_t)att.tv_sec<<32)+((uint64_t)att.tv_nsec<<32)/1000000000;
          // departure_time = ((uint64_t)dtt.tv_sec<<32)+((uint64_t)dtt.tv_nsec<<32)/1000000000;

          return_time = arrival_time - conn->departure_time;

          // uint64_t rtus = (return_time * 1000000) >> 32;

          if (((return_time * 1000000) >> 32) < 300000) {

            // debug(2,"Synchronisation ping return time is %f milliseconds.",(rtus*1.0)/1000);

            // distant_receive_time =
            // ((uint64_t)ntohl(*((uint32_t*)&packet[16])))<<32+ntohl(*((uint32_t*)&packet[20]));

            distant_receive_time = (uint64_t)nctohl(&packet[16]) << 32;
            distant_receive_time += nctohl(&packet[20]);

            // distant_transmit_time =
            // ((uint64_t)ntohl(*((uint32_t*)&packet[24])))<<32+ntohl(*((uint32_t*)&packet[28]));

            distant_transmit_time = (uint64_t)nctohl(&packet[24]) << 32;
            distant_transmit_time += nctohl(&packet[28]);

            // processing_time = distant_transmit_time - distant_receive_time;

            // debug(1,"Return trip time: %lluuS, remote processing time:
            // %lluuS.",(return_time*1000000)>>32,(processing_time*1000000)>>32);

            uint64_t local_time_by_remote_clock = distant_transmit_time + return_time / 2;

            unsigned int cc;
            for (cc = time_ping_history - 1; cc > 0; cc--) {
              conn->time_pings[cc] = conn->time_pings[cc - 1];
              conn->time_pings[cc].dispersion =
                  (conn->time_pings[cc].dispersion * 110) /
                  100; // make the dispersions 'age' by this rational factor
            }
            // these are for diagnostics only -- not used
            conn->time_pings[0].local_time = arrival_time;
            conn->time_pings[0].remote_time = distant_transmit_time;

            conn->time_pings[0].local_to_remote_difference =
                local_time_by_remote_clock - arrival_time;
            conn->time_pings[0].dispersion = return_time;
            if (conn->time_ping_count < time_ping_history)
              conn->time_ping_count++;

            uint64_t local_time_chosen = arrival_time;

            // uint64_t remote_time_chosen = distant_transmit_time;
            // now pick the timestamp with the lowest dispersion
            uint64_t l2rtd = conn->time_pings[0].local_to_remote_difference;
            uint64_t tld = conn->time_pings[0].dispersion;
            // chosen = 0;
            for (cc = 1; cc < conn->time_ping_count; cc++)
              if (conn->time_pings[cc].dispersion < tld) {
                l2rtd = conn->time_pings[cc].local_to_remote_difference;
                // chosen = cc;
                tld = conn->time_pings[cc].dispersion;
                local_time_chosen = conn->time_pings[cc].local_time;
                // remote_time_chosen = conn->time_pings[cc].remote_time;
              }
            // int64_t ji;

            if (conn->time_ping_count > 1) {
              if (l2rtd > conn->local_to_remote_time_difference) {
                local_to_remote_time_jitters =
                    local_to_remote_time_jitters + l2rtd - conn->local_to_remote_time_difference;
                //  ji = l2rtd - conn->local_to_remote_time_difference;
              } else {
                local_to_remote_time_jitters =
                    local_to_remote_time_jitters + conn->local_to_remote_time_difference - l2rtd;
                // ji = -(conn->local_to_remote_time_difference - l2rtd);
              }
              local_to_remote_time_jitters_count += 1;
            }
            // uncomment below to print jitter between client's clock and oour clock
            // int64_t rtus = (tld*1000000)>>32; ji = (ji*1000000)>>32; debug(1,"Choosing time
            // difference
            // with dispersion of %lld us with delta of %lld us",rtus,ji);

            conn->local_to_remote_time_difference = l2rtd;
            if (first_local_to_remote_time_difference == 0) {
              first_local_to_remote_time_difference = conn->local_to_remote_time_difference;
              // first_local_to_remote_time_difference_time = get_absolute_time_in_fp();
            }

            // int64_t clock_drift;
            // int64_t clock_drift_in_usec;
            // double clock_drift_ppm = 0.0;
            if (first_local_time == 0) {
              first_local_time = local_time_chosen;
              // first_remote_time = remote_time_chosen;
              // clock_drift = 0;
            } else {
              // uint64_t local_time_change = local_time_chosen - first_local_time;
              // uint64_t remote_time_change = remote_time_chosen - first_remote_time;

              /*
              if (remote_time_change >= local_time_change)
                clock_drift = remote_time_change - local_time_change;
              else
                clock_drift = -(local_time_change - remote_time_change);
              */
              /*
              if (clock_drift >= 0)
                clock_drift_in_usec = (clock_drift * 1000000) >> 32;
              else
                clock_drift_in_usec = -(((-clock_drift) * 1000000) >> 32);
              */

              // clock_drift_ppm = (1.0 * clock_drift_in_usec) / (local_time_change >> 32);
            }

            int64_t source_drift_usec;
            if (conn->play_segment_reference_frame != 0) {
              int64_t reference_timestamp;
              uint64_t reference_timestamp_time, remote_reference_timestamp_time;
              get_reference_timestamp_stuff(&reference_timestamp, &reference_timestamp_time,
                                            &remote_reference_timestamp_time, conn);
              uint64_t frame_difference = 0;
              if (reference_timestamp >= conn->play_segment_reference_frame)
                frame_difference =
                    (uint64_t)reference_timestamp - (uint64_t)conn->play_segment_reference_frame;
              else // rollover
                frame_difference = (uint64_t)reference_timestamp + 0x100000000 -
                                   (uint64_t)conn->play_segment_reference_frame;
              uint64_t frame_time_difference_calculated =
                  (((uint64_t)frame_difference << 32) / 44100);
              uint64_t frame_time_difference_actual =
                  remote_reference_timestamp_time -
                  conn->play_segment_reference_frame_remote_time; // this is all done by reference
                                                                  // to
                                                                  // the
                                                                  // sources' system clock
              // debug(1,"%llu frames since play started, %llu usec calculated, %llu usec
              // actual",frame_difference, (frame_time_difference_calculated*1000000)>>32,
              // (frame_time_difference_actual*1000000)>>32);
              if (frame_time_difference_calculated >=
                  frame_time_difference_actual) // i.e. if the time it should have taken to send the
                // packets is greater than the actual time difference
                // measured on the source clock
                // then the source DAC's clock is running fast relative to the source system clock
                source_drift_usec = frame_time_difference_calculated - frame_time_difference_actual;
              else
                // otherwise the source DAC's clock is running slow relative to the source system
                // clock
                source_drift_usec =
                    -(frame_time_difference_actual - frame_time_difference_calculated);
            } else
              source_drift_usec = 0;
            source_drift_usec = (source_drift_usec * 1000000) >> 32; // turn it to microseconds

            // long current_delay = 0;
            // if (config.output->delay) {
            //       config.output->delay(&current_delay);
            //}
            //  Useful for troubleshooting:
            // debug(1, "clock_drift_ppm %f\tchosen %5d\tsource_drift_usec
            // %10.1lld\treturn_time_in_usec
            // %10.1llu",
            // clock_drift_ppm,
            // chosen,
            //(session_corrections*1000000)/44100,
            // current_delay,
            // source_drift_usec,
            // buffer_occupancy,
            //(return_time*1000000)>>32);
          } else {
            debug(2, "Time ping turnaround time: %lld us -- it looks like a timing ping was lost.",
                  (return_time * 1000000) >> 32);
          }
        } else {
          debug(1, "Timing port -- Unknown RTP packet of type 0x%02X length %d.", packet[1], nread);
        }
      } else {
        debug(3, "Timing Receiver Thread -- dropping incoming packet to simulate a bad network.");
      }
    } else {
      debug(1, "Timing receiver -- error receiving a packet.");
    }
  }

  debug(1, "Timing Receiver RTP thread \"normal\" exit -- this can't happen. Hah!");
  pthread_cleanup_pop(0); // don't execute anything here.
  debug(2, "Timing Receiver RTP thread exit.");
  pthread_exit(NULL);
}

static uint16_t bind_port(int ip_family, const char *self_ip_address, uint32_t scope_id,
                          int *sock) {
  // look for a port in the range, if any was specified.
  uint16_t desired_port = config.udp_port_base;
  int ret = 0;

  int local_socket = socket(ip_family, SOCK_DGRAM, IPPROTO_UDP);
  if (local_socket == -1)
    die("Could not allocate a socket.");
  SOCKADDR myaddr;
  do {
    memset(&myaddr, 0, sizeof(myaddr));
    if (ip_family == AF_INET) {
      struct sockaddr_in *sa = (struct sockaddr_in *)&myaddr;
      sa->sin_family = AF_INET;
      sa->sin_port = ntohs(desired_port);
      inet_pton(AF_INET, self_ip_address, &(sa->sin_addr));
      ret = bind(local_socket, (struct sockaddr *)sa, sizeof(struct sockaddr_in));
    }
#ifdef AF_INET6
    if (ip_family == AF_INET6) {
      struct sockaddr_in6 *sa6 = (struct sockaddr_in6 *)&myaddr;
      sa6->sin6_family = AF_INET6;
      sa6->sin6_port = ntohs(desired_port);
      inet_pton(AF_INET6, self_ip_address, &(sa6->sin6_addr));
      sa6->sin6_scope_id = scope_id;
      ret = bind(local_socket, (struct sockaddr *)sa6, sizeof(struct sockaddr_in6));
    }
#endif

  } while ((ret < 0) && (errno == EADDRINUSE) && (desired_port != 0) &&
           (++desired_port < config.udp_port_base + config.udp_port_range));

  // debug(1,"UDP port chosen: %d.",desired_port);

  if (ret < 0) {
    close(local_socket);
    die("error: could not bind a UDP port! Check the udp_port_range is large enough (>= 10) or "
        "check for restrictive firewall settings or a bad router!");
  }

  uint16_t sport;
  SOCKADDR local;
  socklen_t local_len = sizeof(local);
  getsockname(local_socket, (struct sockaddr *)&local, &local_len);
#ifdef AF_INET6
  if (local.SAFAMILY == AF_INET6) {
    struct sockaddr_in6 *sa6 = (struct sockaddr_in6 *)&local;
    sport = ntohs(sa6->sin6_port);
  } else
#endif
  {
    struct sockaddr_in *sa = (struct sockaddr_in *)&local;
    sport = ntohs(sa->sin_port);
  }
  *sock = local_socket;
  return sport;
}

void rtp_setup(SOCKADDR *local, SOCKADDR *remote, uint16_t cport, uint16_t tport,
               rtsp_conn_info *conn) {

  // this gets the local and remote ip numbers (and ports used for the TCD stuff)
  // we use the local stuff to specify the address we are coming from and
  // we use the remote stuff to specify where we're goint to

  if (conn->rtp_running)
    warn("rtp_setup has been called with al already-active stream -- ignored. Possible duplicate "
         "SETUP call?");
  else {

    debug(3, "rtp_setup: cport=%d tport=%d.", cport, tport);

    // print out what we know about the client
    void *client_addr = NULL, *self_addr = NULL;
    // int client_port, self_port;
    // char client_port_str[64];
    // char self_addr_str[64];

    conn->connection_ip_family =
        remote->SAFAMILY; // keep information about the kind of ip of the client

#ifdef AF_INET6
    if (conn->connection_ip_family == AF_INET6) {
      struct sockaddr_in6 *sa6 = (struct sockaddr_in6 *)remote;
      client_addr = &(sa6->sin6_addr);
      // client_port = ntohs(sa6->sin6_port);
      sa6 = (struct sockaddr_in6 *)local;
      self_addr = &(sa6->sin6_addr);
      // self_port = ntohs(sa6->sin6_port);
      conn->self_scope_id = sa6->sin6_scope_id;
    }
#endif
    if (conn->connection_ip_family == AF_INET) {
      struct sockaddr_in *sa4 = (struct sockaddr_in *)remote;
      client_addr = &(sa4->sin_addr);
      // client_port = ntohs(sa4->sin_port);
      sa4 = (struct sockaddr_in *)local;
      self_addr = &(sa4->sin_addr);
      // self_port = ntohs(sa4->sin_port);
    }

    inet_ntop(conn->connection_ip_family, client_addr, conn->client_ip_string,
              sizeof(conn->client_ip_string));
    inet_ntop(conn->connection_ip_family, self_addr, conn->self_ip_string,
              sizeof(conn->self_ip_string));

    debug(2, "Connection %d: SETUP -- Connection from %s to self at %s.", conn->connection_number,
          conn->client_ip_string, conn->self_ip_string);

    // set up a the record of the remote's control socket
    struct addrinfo hints;
    struct addrinfo *servinfo;

    memset(&conn->rtp_client_control_socket, 0, sizeof(conn->rtp_client_control_socket));
    memset(&hints, 0, sizeof hints);
    hints.ai_family = conn->connection_ip_family;
    hints.ai_socktype = SOCK_DGRAM;
    char portstr[20];
    snprintf(portstr, 20, "%d", cport);
    if (getaddrinfo(conn->client_ip_string, portstr, &hints, &servinfo) != 0)
      die("Can't get address of client's control port");

#ifdef AF_INET6
    if (servinfo->ai_family == AF_INET6) {
      memcpy(&conn->rtp_client_control_socket, servinfo->ai_addr, sizeof(struct sockaddr_in6));
      // ensure the scope id matches that of remote. this is needed for link-local addresses.
      struct sockaddr_in6 *sa6 = (struct sockaddr_in6 *)&conn->rtp_client_control_socket;
      sa6->sin6_scope_id = conn->self_scope_id;
    } else
#endif
      memcpy(&conn->rtp_client_control_socket, servinfo->ai_addr, sizeof(struct sockaddr_in));
    freeaddrinfo(servinfo);

    // set up a the record of the remote's timing socket
    memset(&conn->rtp_client_timing_socket, 0, sizeof(conn->rtp_client_timing_socket));
    memset(&hints, 0, sizeof hints);
    hints.ai_family = conn->connection_ip_family;
    hints.ai_socktype = SOCK_DGRAM;
    snprintf(portstr, 20, "%d", tport);
    if (getaddrinfo(conn->client_ip_string, portstr, &hints, &servinfo) != 0)
      die("Can't get address of client's timing port");
#ifdef AF_INET6
    if (servinfo->ai_family == AF_INET6) {
      memcpy(&conn->rtp_client_timing_socket, servinfo->ai_addr, sizeof(struct sockaddr_in6));
      // ensure the scope id matches that of remote. this is needed for link-local addresses.
      struct sockaddr_in6 *sa6 = (struct sockaddr_in6 *)&conn->rtp_client_timing_socket;
      sa6->sin6_scope_id = conn->self_scope_id;
    } else
#endif
      memcpy(&conn->rtp_client_timing_socket, servinfo->ai_addr, sizeof(struct sockaddr_in));
    freeaddrinfo(servinfo);

    // now, we open three sockets -- one for the audio stream, one for the timing and one for the
    // control
    conn->remote_control_port = cport;
    conn->remote_timing_port = tport;

    conn->local_control_port = bind_port(conn->connection_ip_family, conn->self_ip_string,
                                         conn->self_scope_id, &conn->control_socket);
    conn->local_timing_port = bind_port(conn->connection_ip_family, conn->self_ip_string,
                                        conn->self_scope_id, &conn->timing_socket);
    conn->local_audio_port = bind_port(conn->connection_ip_family, conn->self_ip_string,
                                       conn->self_scope_id, &conn->audio_socket);

    debug(3, "listening for audio, control and timing on ports %d, %d, %d.", conn->local_audio_port,
          conn->local_control_port, conn->local_timing_port);

    conn->reference_timestamp = 0;
    // pthread_create(&rtp_audio_thread, NULL, &rtp_audio_receiver, NULL);
    // pthread_create(&rtp_control_thread, NULL, &rtp_control_receiver, NULL);
    // pthread_create(&rtp_timing_thread, NULL, &rtp_timing_receiver, NULL);

    conn->request_sent = 0;
    conn->rtp_running = 1;

#ifdef CONFIG_METADATA
    send_ssnc_metadata('clip', strdup(conn->client_ip_string), strlen(conn->client_ip_string), 1);
    send_ssnc_metadata('svip', strdup(conn->self_ip_string), strlen(conn->self_ip_string), 1);
#endif
  }
}

void get_reference_timestamp_stuff(int64_t *timestamp, uint64_t *timestamp_time,
                                   uint64_t *remote_timestamp_time, rtsp_conn_info *conn) {
  // types okay
  debug_mutex_lock(&conn->reference_time_mutex, 1000, 1);
  *timestamp = conn->reference_timestamp;
  *timestamp_time = conn->reference_timestamp_time;
  // if ((*timestamp == 0) && (*timestamp_time == 0)) {
  //  debug(1,"Reference timestamp is invalid.");
  //}
  *remote_timestamp_time = conn->remote_reference_timestamp_time;
  debug_mutex_unlock(&conn->reference_time_mutex, 3);
}

void clear_reference_timestamp(rtsp_conn_info *conn) {
  debug_mutex_lock(&conn->reference_time_mutex, 1000, 1);
  conn->reference_timestamp = 0;
  conn->reference_timestamp_time = 0;
  debug_mutex_unlock(&conn->reference_time_mutex, 3);
}

void rtp_request_resend(seq_t first, uint32_t count, rtsp_conn_info *conn) {
  if (conn->rtp_running) {
    // if (!request_sent) {
    // debug(2, "requesting resend of %d packets starting at %u.", count, first);
    //  request_sent = 1;
    //}

    char req[8]; // *not* a standard RTCP NACK
    req[0] = 0x80;
    req[1] = (char)0x55 | (char)0x80;            // Apple 'resend'
    *(unsigned short *)(req + 2) = htons(1);     // our sequence number
    *(unsigned short *)(req + 4) = htons(first); // missed seqnum
    *(unsigned short *)(req + 6) = htons(count); // count
    socklen_t msgsize = sizeof(struct sockaddr_in);
#ifdef AF_INET6
    if (conn->rtp_client_control_socket.SAFAMILY == AF_INET6) {
      msgsize = sizeof(struct sockaddr_in6);
    }
#endif
    uint64_t time_of_sending_fp = get_absolute_time_in_fp();
    uint64_t resend_error_backoff_time = (uint64_t)1 << (32 - 4); // one sixteenth of a second
    if ((conn->rtp_time_of_last_resend_request_error_fp == 0) ||
        ((time_of_sending_fp - conn->rtp_time_of_last_resend_request_error_fp) >
         resend_error_backoff_time)) {
      if ((config.diagnostic_drop_packet_fraction == 0.0) ||
          (drand48() > config.diagnostic_drop_packet_fraction)) {
        // put a time limit on the sendto

        struct timeval timeout;
        timeout.tv_sec = 0;
        timeout.tv_usec = 100000;

        if (setsockopt(conn->control_socket, SOL_SOCKET, SO_SNDTIMEO, (char *)&timeout,
                       sizeof(timeout)) < 0)
          debug(1, "Can't set timeout on resend request socket.");

        if (sendto(conn->control_socket, req, sizeof(req), 0,
                   (struct sockaddr *)&conn->rtp_client_control_socket, msgsize) == -1) {
          char em[1024];
          strerror_r(errno, em, sizeof(em));
          debug(1, "Error %d using sendto to an audio socket: \"%s\". Backing off for 1/16th of a "
                   "second.",
                errno, em);
          conn->rtp_time_of_last_resend_request_error_fp = time_of_sending_fp;
        } else {
          conn->rtp_time_of_last_resend_request_error_fp = 0;
        }

      } else {
        debug(
            3,
            "Dropping resend request packet to simulate a bad network. Backing off for 1/16th of a "
            "second.");
        conn->rtp_time_of_last_resend_request_error_fp = time_of_sending_fp;
      }
    } else {
      debug(3, "Backing off sending resend requests due to a previous send-to error");
    }
  } else {
    // if (!request_sent) {
    debug(2, "rtp_request_resend called without active stream!");
    //  request_sent = 1;
    //}
  }
}