Cast: Logging estimates clock difference based on packets

media/cast/logging/receiver_time_offset_estimator_impl.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <algorithm>
 #include <utility>
 
 #include "base/logging.h"
 #include "base/time/tick_clock.h"
 #include "media/cast/logging/receiver_time_offset_estimator_impl.h"
 
 namespace media {
 namespace cast {
 
-// This should be large enough so that we can collect all 3 events before
-// the entry gets removed from the map.
-const size_t kMaxEventTimesMapSize = 100;
+ReceiverTimeOffsetEstimatorImpl::BoundCalculator::BoundCalculator()
+    : has_bound_(false) {}
+ReceiverTimeOffsetEstimatorImpl::BoundCalculator::~BoundCalculator() {}
 
-ReceiverTimeOffsetEstimatorImpl::ReceiverTimeOffsetEstimatorImpl(
-    base::TickClock* clock)
-    : bounded_(false),
-      clock_(clock),
-      offset_bounds_valid_(false),
-      last_reset_time_(clock_->NowTicks()) {
+void ReceiverTimeOffsetEstimatorImpl::BoundCalculator::SetSent(
+    uint32 rtp,
+    uint32 packet_id,
+    bool audio,
+    base::TimeTicks t) {
+  uint64 key = (static_cast<uint64>(rtp) << 32) | (packet_id << 1) | audio;
+  events_[key].first = t;
+  CheckUpdate(key);
+}
+
+void ReceiverTimeOffsetEstimatorImpl::BoundCalculator::SetReceived(
+    uint32 rtp,
+    uint16 packet_id,
+    bool audio,
+    base::TimeTicks t) {
+  uint64 key = (static_cast<uint64>(rtp) << 32) | (packet_id << 1) | audio;
+  events_[key].second = t;
+  CheckUpdate(key);
+}
+
+void ReceiverTimeOffsetEstimatorImpl::BoundCalculator::UpdateBound(
+    base::TimeTicks sent, base::TimeTicks received) {
+    base::TimeDelta delta = received - sent;
+    if (has_bound_) {
+      if (delta < bound_) {
+        bound_ = delta;
+      } else {
+        bound_ += (delta - bound_) / kClockDriftSpeed;

[imcheng, 2014/09/09 01:04:23]

What does this do? Does it handle drifting in either direction?

[hubbe, 2014/09/09 19:06:15]

Added some (hopefully helpful) comments to the class.

+      }
+    } else {
+      bound_ = delta;
+    }
+    has_bound_ = true;
+  }
+
+void ReceiverTimeOffsetEstimatorImpl::BoundCalculator::CheckUpdate(
+    uint64 key) {
+  TimeTickPair &ticks = events_[key];

[imcheng, 2014/09/09 01:04:23]

const?

[hubbe, 2014/09/09 19:06:15]

Done.

+  if (!ticks.first.is_null() && !ticks.second.is_null()) {
+    UpdateBound(ticks.first, ticks.second);
+    events_.erase(key);
+    return;
+  }
+
+  if (events_.size() > kMaxEventTimesMapSize) {
+    EventMap::iterator i = ModMapOldest(&events_);
+    if (i != events_.end()) {
+      events_.erase(i);
+    }
+  }
+}
+
+ReceiverTimeOffsetEstimatorImpl::ReceiverTimeOffsetEstimatorImpl() {
 }
 
 ReceiverTimeOffsetEstimatorImpl::~ReceiverTimeOffsetEstimatorImpl() {
   DCHECK(thread_checker_.CalledOnValidThread());
 }
 
+
 void ReceiverTimeOffsetEstimatorImpl::OnReceiveFrameEvent(
     const FrameEvent& frame_event) {
   DCHECK(thread_checker_.CalledOnValidThread());
-
-  if (frame_event.media_type != VIDEO_EVENT)
-    return;
-
-  CastLoggingEvent event = frame_event.type;
-  if (event != FRAME_ENCODED && event != FRAME_ACK_SENT &&
-      event != FRAME_ACK_RECEIVED)
-    return;
-
-  EventTimesMap::iterator it = event_times_map_.find(frame_event.rtp_timestamp);
-  if (it == event_times_map_.end()) {
-    EventTimes event_times;
-    it = event_times_map_.insert(std::make_pair(frame_event.rtp_timestamp,
-                                                event_times)).first;
-  }
-  switch (event) {
-    case FRAME_ENCODED:
-      // Encode is supposed to happen only once. If we see duplicate event,
-      // throw away the entry.
-      if (it->second.event_a_time.is_null()) {
-        it->second.event_a_time = frame_event.timestamp;
-      } else {
-        event_times_map_.erase(it);
-        return;
-      }
-      break;
+  switch (frame_event.type) {
     case FRAME_ACK_SENT:
-      if (it->second.event_b_time.is_null()) {
-        it->second.event_b_time = frame_event.timestamp;
-      } else if (it->second.event_b_time != frame_event.timestamp) {
-        // Duplicate ack sent events are normal due to RTCP redundancy,
-        // but they must have the same event timestamp.
-        event_times_map_.erase(it);
-        return;
-      }
+      lower_bound_.SetSent(frame_event.rtp_timestamp,
+                           0,
+                           frame_event.media_type == AUDIO_EVENT,
+                           frame_event.timestamp);
       break;
     case FRAME_ACK_RECEIVED:
-      // If there are duplicate ack received events, pick the one with the
-      // smallest event timestamp so we can get a better bound.
-      if (it->second.event_c_time.is_null()) {
-        it->second.event_c_time = frame_event.timestamp;
-      } else {
-        it->second.event_c_time =
-            std::min(frame_event.timestamp, it->second.event_c_time);
-      }
+      lower_bound_.SetReceived(frame_event.rtp_timestamp,
+                               0,
+                               frame_event.media_type == AUDIO_EVENT,
+                               frame_event.timestamp);
       break;
     default:
-      NOTREACHED();
+      // Ignored
+      break;
   }
-
-  if (!it->second.event_a_time.is_null() &&
-      !it->second.event_b_time.is_null() &&
-      !it->second.event_c_time.is_null()) {
-    UpdateOffsetBounds(it->second);
-    event_times_map_.erase(it);
-  }
-
-  // Keep the map size at most |kMaxEventTimesMapSize|.
-  if (event_times_map_.size() > kMaxEventTimesMapSize)
-    event_times_map_.erase(event_times_map_.begin());
 }
 
 bool ReceiverTimeOffsetEstimatorImpl::GetReceiverOffsetBounds(
     base::TimeDelta* lower_bound,
     base::TimeDelta* upper_bound) {
-  if (!bounded_)
+  if (!lower_bound_.has_bound() || !upper_bound_.has_bound())
     return false;
 
-  *lower_bound = prev_offset_lower_bound_;
-  *upper_bound = prev_offset_upper_bound_;
+  *lower_bound = -lower_bound_.bound();
+  *upper_bound = upper_bound_.bound();
+
+  // Sanitize the output, we don't want the upper bound to be
+  // lower than the lower bound, make them the same.
+  if (upper_bound < lower_bound) {
+    lower_bound += (lower_bound - upper_bound) / 2;
+    upper_bound = lower_bound;
+  }
   return true;
 }
 
 void ReceiverTimeOffsetEstimatorImpl::OnReceivePacketEvent(
     const PacketEvent& packet_event) {
-  // Not interested in packet events.
   DCHECK(thread_checker_.CalledOnValidThread());
+  switch (packet_event.type) {
+    case PACKET_SENT_TO_NETWORK:
+      upper_bound_.SetSent(packet_event.rtp_timestamp,
+                           packet_event.packet_id,
+                           packet_event.media_type == AUDIO_EVENT,
+                           packet_event.timestamp);
+      break;
+    case PACKET_RECEIVED:
+      upper_bound_.SetReceived(packet_event.rtp_timestamp,
+                               packet_event.packet_id,
+                               packet_event.media_type == AUDIO_EVENT,
+                               packet_event.timestamp);
+      break;
+    default:
+      // Ignored
+      break;
+  }
 }
 
-void ReceiverTimeOffsetEstimatorImpl::UpdateOffsetBounds(
-    const EventTimes& event) {
-  base::TimeDelta lower_bound = event.event_b_time - event.event_c_time;
-  base::TimeDelta upper_bound = event.event_b_time - event.event_a_time;
-
-  if (offset_bounds_valid_) {
-    lower_bound = std::max(lower_bound, offset_lower_bound_);
-    upper_bound = std::min(upper_bound, offset_upper_bound_);
-  }
-
-  if (lower_bound > upper_bound) {
-    VLOG(2) << "Got bogus offset bound values [" << lower_bound.InMilliseconds()
-            << ", " << upper_bound.InMilliseconds() << "].";
-    return;
-  }
-
-  offset_lower_bound_ = lower_bound;
-  offset_upper_bound_ = upper_bound;
-  offset_bounds_valid_ = true;
-  if (!bounded_ ||
-      offset_upper_bound_ - offset_lower_bound_ <
-          base::TimeDelta::FromMilliseconds(20)) {
-    prev_offset_lower_bound_ = offset_lower_bound_;
-    prev_offset_upper_bound_ = offset_upper_bound_;
-  }
-
-  base::TimeTicks now = clock_->NowTicks();
-  if (now - last_reset_time_ > base::TimeDelta::FromSeconds(20)) {
-    last_reset_time_ = now;
-    offset_lower_bound_ = base::TimeDelta();
-    offset_upper_bound_ = base::TimeDelta();
-    offset_bounds_valid_ = false;
-  }
-
-  bounded_ = true;
-}
 
 }  // namespace cast
 }  // namespace media