Allow pacer to boost bitrate in order to meet time constraints.

webrtc/modules/pacing/paced_sender.cc

Index: webrtc/modules/pacing/paced_sender.cc
diff --git a/webrtc/modules/pacing/paced_sender.cc b/webrtc/modules/pacing/paced_sender.cc
index 3c299f827ee1654b4bd6aa011d5abd2393a95aee..e38405a6a24faa71145f89eb36b88a6b4c988493 100644
--- a/webrtc/modules/pacing/paced_sender.cc
+++ b/webrtc/modules/pacing/paced_sender.cc
@@ -10,12 +10,11 @@
 
 #include "webrtc/modules/pacing/paced_sender.h"
 
-#include <assert.h>
-
 #include <map>
 #include <queue>
 #include <set>
 
+#include "webrtc/base/checks.h"
 #include "webrtc/modules/include/module_common_types.h"
 #include "webrtc/modules/pacing/bitrate_prober.h"
 #include "webrtc/system_wrappers/include/clock.h"
@@ -86,7 +85,11 @@ struct Comparator {
 // Class encapsulating a priority queue with some extensions.
 class PacketQueue {
  public:
-  PacketQueue() : bytes_(0) {}
+  explicit PacketQueue(Clock* clock)
+      : bytes_(0),
+        clock_(clock),
+        queue_time_sum_(0),
+        time_last_updated_(clock_->TimeInMilliseconds()) {}
   virtual ~PacketQueue() {}
 
   void Push(const Packet& packet) {
@@ -114,6 +117,7 @@ class PacketQueue {
   void FinalizePop(const Packet& packet) {
     RemoveFromDupeSet(packet);
     bytes_ -= packet.bytes;
+    queue_time_sum_ -= (time_last_updated_ - packet.enqueue_time_ms);
     packet_list_.erase(packet.this_it);
   }
 
@@ -123,13 +127,22 @@ class PacketQueue {
 
   uint64_t SizeInBytes() const { return bytes_; }
 
-  int64_t OldestEnqueueTime() const {
-    std::list<Packet>::const_reverse_iterator it = packet_list_.rbegin();
+  int64_t OldestEnqueueTimeMs() const {
+    auto it = packet_list_.rbegin();
     if (it == packet_list_.rend())
       return 0;
     return it->enqueue_time_ms;
   }
 
+  int64_t AverageQueueTimeMs() {
+    int64_t now = clock_->TimeInMilliseconds();
+    RTC_DCHECK_GE(now, time_last_updated_);
+    int64_t delta = now - time_last_updated_;
+    queue_time_sum_ += delta * prio_queue_.size();
+    time_last_updated_ = now;
+    return queue_time_sum_ / prio_queue_.size();
+  }
+
  private:
   // Try to add a packet to the set of ssrc/seqno identifiers currently in the
   // queue. Return true if inserted, false if this is a duplicate.
@@ -147,7 +160,7 @@ class PacketQueue {
 
   void RemoveFromDupeSet(const Packet& packet) {
     SsrcSeqNoMap::iterator it = dupe_map_.find(packet.ssrc);
-    assert(it != dupe_map_.end());
+    RTC_DCHECK(it != dupe_map_.end());
     it->second.erase(packet.sequence_number);
     if (it->second.empty()) {
       dupe_map_.erase(it);
@@ -165,6 +178,9 @@ class PacketQueue {
   // Map<ssrc, set<seq_no> >, for checking duplicates.
   typedef std::map<uint32_t, std::set<uint16_t> > SsrcSeqNoMap;
   SsrcSeqNoMap dupe_map_;
+  Clock* const clock_;
+  int64_t queue_time_sum_;
+  int64_t time_last_updated_;
 };
 
 class IntervalBudget {
@@ -209,6 +225,7 @@ class IntervalBudget {
 };
 }  // namespace paced_sender
 
+const int64_t PacedSender::kMaxQueueLengthMs = 2000;
 const float PacedSender::kDefaultPaceMultiplier = 2.5f;
 
 PacedSender::PacedSender(Clock* clock,
@@ -225,8 +242,9 @@ PacedSender::PacedSender(Clock* clock,
       padding_budget_(new paced_sender::IntervalBudget(min_bitrate_kbps)),
       prober_(new BitrateProber()),
       bitrate_bps_(1000 * bitrate_kbps),
+      max_bitrate_kbps_(max_bitrate_kbps),
       time_last_update_us_(clock->TimeInMicroseconds()),
-      packets_(new paced_sender::PacketQueue()),
+      packets_(new paced_sender::PacketQueue(clock)),
       packet_counter_(0) {
   UpdateBytesPerInterval(kMinPacketLimitMs);
 }
@@ -244,7 +262,7 @@ void PacedSender::Resume() {
 }
 
 void PacedSender::SetProbingEnabled(bool enabled) {
-  assert(packet_counter_ == 0);
+  RTC_CHECK_EQ(0u, packet_counter_);
   probing_enabled_ = enabled;
 }
 
@@ -252,9 +270,12 @@ void PacedSender::UpdateBitrate(int bitrate_kbps,
                                 int max_bitrate_kbps,
                                 int min_bitrate_kbps) {
   CriticalSectionScoped cs(critsect_.get());
-  media_budget_->set_target_rate_kbps(max_bitrate_kbps);
+  // Don't set media bitrate here as it may be boosted in order to meet max
+  // queue time constraint. Just update max_bitrate_kbps_ and let media_budget_
+  // be updated in Process().
   padding_budget_->set_target_rate_kbps(min_bitrate_kbps);
   bitrate_bps_ = 1000 * bitrate_kbps;
+  max_bitrate_kbps_ = max_bitrate_kbps;
 }
 
 void PacedSender::InsertPacket(RtpPacketSender::Priority priority,
@@ -265,14 +286,12 @@ void PacedSender::InsertPacket(RtpPacketSender::Priority priority,
                                bool retransmission) {
   CriticalSectionScoped cs(critsect_.get());
 
-  if (probing_enabled_ && !prober_->IsProbing()) {
+  if (probing_enabled_ && !prober_->IsProbing())
     prober_->SetEnabled(true);
-  }
   prober_->MaybeInitializeProbe(bitrate_bps_);
 
-  if (capture_time_ms < 0) {
+  if (capture_time_ms < 0)
     capture_time_ms = clock_->TimeInMilliseconds();
-  }
 
   packets_->Push(paced_sender::Packet(
       priority, ssrc, sequence_number, capture_time_ms,
@@ -281,9 +300,8 @@ void PacedSender::InsertPacket(RtpPacketSender::Priority priority,
 
 int64_t PacedSender::ExpectedQueueTimeMs() const {
   CriticalSectionScoped cs(critsect_.get());
-  int target_rate = media_budget_->target_rate_kbps();
-  assert(target_rate > 0);
-  return static_cast<int64_t>(packets_->SizeInBytes() * 8 / target_rate);
+  RTC_DCHECK_GT(max_bitrate_kbps_, 0);
+  return static_cast<int64_t>(packets_->SizeInBytes() * 8 / max_bitrate_kbps_);
 }
 
 size_t PacedSender::QueueSizePackets() const {
@@ -294,7 +312,7 @@ size_t PacedSender::QueueSizePackets() const {
 int64_t PacedSender::QueueInMs() const {
   CriticalSectionScoped cs(critsect_.get());
 
-  int64_t oldest_packet = packets_->OldestEnqueueTime();
+  int64_t oldest_packet = packets_->OldestEnqueueTimeMs();
   if (oldest_packet == 0)
     return 0;
 
@@ -305,9 +323,8 @@ int64_t PacedSender::TimeUntilNextProcess() {
   CriticalSectionScoped cs(critsect_.get());
   if (prober_->IsProbing()) {
     int64_t ret = prober_->TimeUntilNextProbe(clock_->TimeInMilliseconds());
-    if (ret >= 0) {
+    if (ret >= 0)
       return ret;
-    }
   }
   int64_t elapsed_time_us = clock_->TimeInMicroseconds() - time_last_update_us_;
   int64_t elapsed_time_ms = (elapsed_time_us + 500) / 1000;
@@ -321,14 +338,29 @@ int32_t PacedSender::Process() {
   time_last_update_us_ = now_us;
   if (paused_)
     return 0;
+  int target_bitrate_kbps = max_bitrate_kbps_;
   if (elapsed_time_ms > 0) {
+    size_t queue_size_bytes = packets_->SizeInBytes();
+    if (queue_size_bytes > 0) {
+      // Assuming equal size packets and input/output rate, the average packet
+      // has avg_time_left_ms left to get queue_size_bytes out of the queue, if
+      // time constraint shall be met. Determine bitrate needed for that.
+      int64_t avg_time_left_ms = std::max<int64_t>(
+          1, kMaxQueueLengthMs - packets_->AverageQueueTimeMs());
+      int min_bitrate_needed_kbps =
+          static_cast<int>(queue_size_bytes * 8 / avg_time_left_ms);
+      if (min_bitrate_needed_kbps > target_bitrate_kbps)
+        target_bitrate_kbps = min_bitrate_needed_kbps;
+    }
+
+    media_budget_->set_target_rate_kbps(target_bitrate_kbps);
+
     int64_t delta_time_ms = std::min(kMaxIntervalTimeMs, elapsed_time_ms);
     UpdateBytesPerInterval(delta_time_ms);
   }
   while (!packets_->Empty()) {
-    if (media_budget_->bytes_remaining() == 0 && !prober_->IsProbing()) {
+    if (media_budget_->bytes_remaining() == 0 && !prober_->IsProbing())
       return 0;
-    }
 
     // Since we need to release the lock in order to send, we first pop the
     // element from the priority queue but keep it in storage, so that we can
@@ -337,9 +369,8 @@ int32_t PacedSender::Process() {
     if (SendPacket(packet)) {
       // Send succeeded, remove it from the queue.
       packets_->FinalizePop(packet);
-      if (prober_->IsProbing()) {
+      if (prober_->IsProbing())
         return 0;
-      }
     } else {
       // Send failed, put it back into the queue.
       packets_->CancelPop(packet);
@@ -351,10 +382,11 @@ int32_t PacedSender::Process() {
     return 0;
 
   size_t padding_needed;
-  if (prober_->IsProbing())
+  if (prober_->IsProbing()) {
     padding_needed = prober_->RecommendedPacketSize();
-  else
+  } else {
     padding_needed = padding_budget_->bytes_remaining();
+  }
 
   if (padding_needed > 0)
     SendPadding(static_cast<size_t>(padding_needed));