From: Mike Brady <4265913+mikebrady@users.noreply.github.com>
Date: Wed, 12 May 2021 09:59:33 +0000 (+0100)
Subject: fix calculation of offset with a negative offset
X-Git-Tag: 4.0-dev~12
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=171001ffd85d1f6ad7dda76694ce1caf7f3f39ed;p=thirdparty%2Fshairport-sync.git

fix calculation of offset with a negative offset
---

diff --git a/rtp.c b/rtp.c
index 3db75e1b..3193eacb 100644
--- a/rtp.c
+++ b/rtp.c
@@ -290,8 +290,8 @@ void *rtp_control_receiver(void *arg) {
                                                                 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
@@ -302,19 +302,19 @@ void *rtp_control_receiver(void *arg) {
                                                               // 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 packet 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 "
@@ -364,17 +364,12 @@ void *rtp_control_receiver(void *arg) {
                                                                              // loop around in
                                                                              // modulo. Not sure if
                                                                              // you'll get an error!
-              // debug(3, "Latency derived just from the sync packet is %" PRIu32 " frames.", la);
+              // debug(1, "Latency from the sync packet is %" PRIu32 " 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);
+                 // debug(1, "Latency offset by %" PRIu32" frames due to the source flags and version giving a latency of %" PRIu32 " frames.", config.fixedLatencyOffset, la);
               }
               if ((conn->maximum_latency) && (conn->maximum_latency < la))
                 la = conn->maximum_latency;
@@ -394,7 +389,9 @@ void *rtp_control_receiver(void *arg) {
                 // here we have the latency but it does not yet account for the
                 // audio_backend_latency_offset
                 int32_t latency_offset =
-                    (uint32_t)(config.audio_backend_latency_offset * conn->input_rate);
+                    (int32_t)(config.audio_backend_latency_offset * conn->input_rate);
+
+                // debug(1,"latency offset is %" PRId32 ", input rate is %u", latency_offset, conn->input_rate);
                 int32_t adjusted_latency = latency_offset + (int32_t)la;
                 if ((adjusted_latency < 0) ||
                     (adjusted_latency >
@@ -411,7 +408,7 @@ void *rtp_control_receiver(void *arg) {
                         ", minimum latency: %" PRIu32 ", maximum "
                         "latency: %" PRIu32 ", fixed offset: %" PRIu32
                         ", audio_backend_latency_offset: %f.",
-                        la, sync_rtp_timestamp - rtp_timestamp_less_latency, conn->minimum_latency,
+                        conn->latency, sync_rtp_timestamp - rtp_timestamp_less_latency, conn->minimum_latency,
                         conn->maximum_latency, config.fixedLatencyOffset,
                         config.audio_backend_latency_offset);
                 }