StartTimestamp generated randomly in RtpSender constructor

webrtc/modules/rtp_rtcp/source/rtp_sender.cc

Index: webrtc/modules/rtp_rtcp/source/rtp_sender.cc
diff --git a/webrtc/modules/rtp_rtcp/source/rtp_sender.cc b/webrtc/modules/rtp_rtcp/source/rtp_sender.cc
index b918a908a7d03d0420b1a4e0e08201f1834e4c91..a6dfb341af0f3e844b993f8998407d3f21fb72a1 100644
--- a/webrtc/modules/rtp_rtcp/source/rtp_sender.cc
+++ b/webrtc/modules/rtp_rtcp/source/rtp_sender.cc
@@ -109,8 +109,6 @@ RTPSender::RTPSender(
       send_packet_observer_(send_packet_observer),
       bitrate_callback_(bitrate_callback),
       // RTP variables
-      start_timestamp_forced_(false),
-      start_timestamp_(0),
       ssrc_db_(SSRCDatabase::GetSSRCDatabase()),
       remote_ssrc_(0),
       sequence_number_forced_(false),
@@ -128,6 +126,7 @@ RTPSender::RTPSender(
   ssrc_rtx_ = ssrc_db_->CreateSSRC();
   RTC_DCHECK(ssrc_rtx_ != 0);
 
+  timestamp_offset_ = random_.Rand<uint32_t>();

[terelius, 2016/08/15 14:56:03]

Note that this PRNG is not cryptographic strength. It is also not seeded with
enough entropy for cryptographic purposes. In fact, it has even less entropy
than what is suggested in the RFC 3550.

[danilchap, 2016/08/15 15:23:17]

Done. Simple note added.

   // Random start, 16 bits. Can't be 0.
   sequence_number_rtx_ = random_.Rand(1, kMaxInitRtpSeqNumber);
   sequence_number_ = random_.Rand(1, kMaxInitRtpSeqNumber);
@@ -1099,7 +1098,7 @@ int32_t RTPSender::BuildRtpHeader(uint8_t* data_buffer,
   if (!sending_media_)
     return -1;
 
-  timestamp_ = start_timestamp_ + capture_timestamp;
+  timestamp_ = timestamp_offset_ + capture_timestamp;
   last_timestamp_time_ms_ = clock_->TimeInMilliseconds();
   uint32_t sequence_number = sequence_number_++;
   capture_time_ms_ = capture_time_ms;
@@ -1499,13 +1498,7 @@ bool RTPSender::UpdateTransportSequenceNumber(RtpPacketToSend* packet,
 }
 
 void RTPSender::SetSendingStatus(bool enabled) {
-  if (enabled) {
-    uint32_t frequency_hz = SendPayloadFrequency();
-    uint32_t RTPtime = CurrentRtp(*clock_, frequency_hz);
-
-    // Will be ignored if it's already configured via API.
-    SetStartTimestamp(RTPtime, false);
-  } else {
+  if (!enabled) {
     rtc::CritScope lock(&send_critsect_);
     if (!ssrc_forced_) {
       // Generate a new SSRC.
@@ -1536,21 +1529,14 @@ uint32_t RTPSender::Timestamp() const {
   return timestamp_;
 }
 
-void RTPSender::SetStartTimestamp(uint32_t timestamp, bool force) {
+void RTPSender::SetTimestampOffset(uint32_t timestamp) {
   rtc::CritScope lock(&send_critsect_);
-  if (force) {
-    start_timestamp_forced_ = true;
-    start_timestamp_ = timestamp;
-  } else {
-    if (!start_timestamp_forced_) {
-      start_timestamp_ = timestamp;
-    }
-  }
+  timestamp_offset_ = timestamp;
 }
 
-uint32_t RTPSender::StartTimestamp() const {
+uint32_t RTPSender::TimestampOffset() const {
   rtc::CritScope lock(&send_critsect_);
-  return start_timestamp_;
+  return timestamp_offset_;
 }
 
 uint32_t RTPSender::GenerateNewSSRC() {
@@ -1729,6 +1715,7 @@ void RTPSender::SetRtpState(const RtpState& rtp_state) {
   rtc::CritScope lock(&send_critsect_);
   sequence_number_ = rtp_state.sequence_number;
   sequence_number_forced_ = true;
+  timestamp_offset_ = rtp_state.start_timestamp;

[terelius, 2016/08/15 14:56:03]

Rename start_timestamp in the state struct too?

[danilchap, 2016/08/15 15:23:17]

Prefer to avoid modifying structure in the /include/ subfolder.

   timestamp_ = rtp_state.timestamp;
   capture_time_ms_ = rtp_state.capture_time_ms;
   last_timestamp_time_ms_ = rtp_state.last_timestamp_time_ms;
@@ -1740,7 +1727,7 @@ RtpState RTPSender::GetRtpState() const {
 
   RtpState state;
   state.sequence_number = sequence_number_;
-  state.start_timestamp = start_timestamp_;
+  state.start_timestamp = timestamp_offset_;
   state.timestamp = timestamp_;
   state.capture_time_ms = capture_time_ms_;
   state.last_timestamp_time_ms = last_timestamp_time_ms_;
@@ -1759,7 +1746,7 @@ RtpState RTPSender::GetRtxRtpState() const {
 
   RtpState state;
   state.sequence_number = sequence_number_rtx_;
-  state.start_timestamp = start_timestamp_;
+  state.start_timestamp = timestamp_offset_;
 
   return state;
 }