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fix calculation of offset with a negative offset

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This commit is contained in:
Mike Brady
2021-05-12 10:59:33 +01:00
parent a27f43cf92
commit 171001ffd8
1 changed files with 13 additions and 16 deletions
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rtp.c
+13 -16
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@@ -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);
}