webrtc/modules/video_coding/frame_buffer2.cc - src - Git at Google

 /*
  *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */

 #include "webrtc/modules/video_coding/frame_buffer2.h"

 #include <algorithm>
 #include <cstring>
 #include <queue>

 #include "webrtc/modules/video_coding/include/video_coding_defines.h"
 #include "webrtc/modules/video_coding/jitter_estimator.h"
 #include "webrtc/modules/video_coding/timing.h"
 #include "webrtc/rtc_base/checks.h"
 #include "webrtc/rtc_base/logging.h"
 #include "webrtc/rtc_base/trace_event.h"
 #include "webrtc/system_wrappers/include/clock.h"
 #include "webrtc/system_wrappers/include/metrics.h"

 namespace webrtc {
 namespace video_coding {

 namespace {
 // Max number of frames the buffer will hold.
 constexpr int kMaxFramesBuffered = 600;

 // Max number of decoded frame info that will be saved.
 constexpr int kMaxFramesHistory = 50;
 }  // namespace

 FrameBuffer::FrameBuffer(Clock* clock,
                          VCMJitterEstimator* jitter_estimator,
                          VCMTiming* timing,
                          VCMReceiveStatisticsCallback* stats_callback)
     : clock_(clock),
       new_continuous_frame_event_(false, false),
       jitter_estimator_(jitter_estimator),
       timing_(timing),
       inter_frame_delay_(clock_->TimeInMilliseconds()),
       last_decoded_frame_timestamp_(0),
       last_decoded_frame_it_(frames_.end()),
       last_continuous_frame_it_(frames_.end()),
       num_frames_history_(0),
       num_frames_buffered_(0),
       stopped_(false),
       protection_mode_(kProtectionNack),
       stats_callback_(stats_callback) {}

 FrameBuffer::~FrameBuffer() {}

 FrameBuffer::ReturnReason FrameBuffer::NextFrame(
     int64_t max_wait_time_ms,
     std::unique_ptr<FrameObject>* frame_out) {
   TRACE_EVENT0("webrtc", "FrameBuffer::NextFrame");
   int64_t latest_return_time_ms =
       clock_->TimeInMilliseconds() + max_wait_time_ms;
   int64_t wait_ms = max_wait_time_ms;
   int64_t now_ms = 0;

   do {
     now_ms = clock_->TimeInMilliseconds();
     {
       rtc::CritScope lock(&crit_);
       new_continuous_frame_event_.Reset();
       if (stopped_)
         return kStopped;

       wait_ms = max_wait_time_ms;

       // Need to hold |crit_| in order to use |frames_|, therefore we
       // set it here in the loop instead of outside the loop in order to not
       // acquire the lock unnecesserily.
       next_frame_it_ = frames_.end();

       // |frame_it| points to the first frame after the
       // |last_decoded_frame_it_|.
       auto frame_it = frames_.end();
       if (last_decoded_frame_it_ == frames_.end()) {
         frame_it = frames_.begin();
       } else {
         frame_it = last_decoded_frame_it_;
         ++frame_it;
       }

       // |continuous_end_it| points to the first frame after the
       // |last_continuous_frame_it_|.
       auto continuous_end_it = last_continuous_frame_it_;
       if (continuous_end_it != frames_.end())
         ++continuous_end_it;

       for (; frame_it != continuous_end_it && frame_it != frames_.end();
            ++frame_it) {
         if (!frame_it->second.continuous ||
             frame_it->second.num_missing_decodable > 0) {
           continue;
         }

         FrameObject* frame = frame_it->second.frame.get();
         next_frame_it_ = frame_it;
         if (frame->RenderTime() == -1)
           frame->SetRenderTime(timing_->RenderTimeMs(frame->timestamp, now_ms));
         wait_ms = timing_->MaxWaitingTime(frame->RenderTime(), now_ms);

         // This will cause the frame buffer to prefer high framerate rather
         // than high resolution in the case of the decoder not decoding fast
         // enough and the stream has multiple spatial and temporal layers.
         if (wait_ms == 0)
           continue;

         break;
       }
     }  // rtc::Critscope lock(&crit_);

     wait_ms = std::min<int64_t>(wait_ms, latest_return_time_ms - now_ms);
     wait_ms = std::max<int64_t>(wait_ms, 0);
   } while (new_continuous_frame_event_.Wait(wait_ms));

   {
     rtc::CritScope lock(&crit_);
     now_ms = clock_->TimeInMilliseconds();
     if (next_frame_it_ != frames_.end()) {
       std::unique_ptr<FrameObject> frame =
           std::move(next_frame_it_->second.frame);

       if (!frame->delayed_by_retransmission()) {
         int64_t frame_delay;

         if (inter_frame_delay_.CalculateDelay(frame->timestamp, &frame_delay,
                                               frame->ReceivedTime())) {
           jitter_estimator_->UpdateEstimate(frame_delay, frame->size());
         }

         float rtt_mult = protection_mode_ == kProtectionNackFEC ? 0.0 : 1.0;
         timing_->SetJitterDelay(jitter_estimator_->GetJitterEstimate(rtt_mult));
         timing_->UpdateCurrentDelay(frame->RenderTime(), now_ms);
       }

       // Gracefully handle bad RTP timestamps and render time issues.
       if (HasBadRenderTiming(*frame, now_ms)) {
         jitter_estimator_->Reset();
         timing_->Reset();
         frame->SetRenderTime(timing_->RenderTimeMs(frame->timestamp, now_ms));
       }

       UpdateJitterDelay();
       UpdateTimingFrameInfo();
       PropagateDecodability(next_frame_it_->second);

       // Sanity check for RTP timestamp monotonicity.
       if (last_decoded_frame_it_ != frames_.end()) {
         const FrameKey& last_decoded_frame_key = last_decoded_frame_it_->first;
         const FrameKey& frame_key = next_frame_it_->first;

         const bool frame_is_higher_spatial_layer_of_last_decoded_frame =
             last_decoded_frame_timestamp_ == frame->timestamp &&
             last_decoded_frame_key.picture_id == frame_key.picture_id &&
             last_decoded_frame_key.spatial_layer < frame_key.spatial_layer;

         if (AheadOrAt(last_decoded_frame_timestamp_, frame->timestamp) &&
             !frame_is_higher_spatial_layer_of_last_decoded_frame) {
           // TODO(brandtr): Consider clearing the entire buffer when we hit
           // these conditions.
           LOG(LS_WARNING) << "Frame with (timestamp:picture_id:spatial_id) ("
                           << frame->timestamp << ":" << frame->picture_id << ":"
                           << static_cast<int>(frame->spatial_layer) << ")"
                           << " sent to decoder after frame with"
                           << " (timestamp:picture_id:spatial_id) ("
                           << last_decoded_frame_timestamp_ << ":"
                           << last_decoded_frame_key.picture_id << ":"
                           << static_cast<int>(
                                  last_decoded_frame_key.spatial_layer)
                           << ").";
         }
       }

       AdvanceLastDecodedFrame(next_frame_it_);
       last_decoded_frame_timestamp_ = frame->timestamp;
       *frame_out = std::move(frame);
       return kFrameFound;
     }
   }

   if (latest_return_time_ms - now_ms > 0) {
     // If |next_frame_it_ == frames_.end()| and there is still time left, it
     // means that the frame buffer was cleared as the thread in this function
     // was waiting to acquire |crit_| in order to return. Wait for the
     // remaining time and then return.
     return NextFrame(latest_return_time_ms - now_ms, frame_out);
   }

   return kTimeout;
 }

 bool FrameBuffer::HasBadRenderTiming(const FrameObject& frame, int64_t now_ms) {
   // Assume that render timing errors are due to changes in the video stream.
   int64_t render_time_ms = frame.RenderTimeMs();
   const int64_t kMaxVideoDelayMs = 10000;
   if (render_time_ms < 0) {
     return true;
   }
   if (std::abs(render_time_ms - now_ms) > kMaxVideoDelayMs) {
     int frame_delay = static_cast<int>(std::abs(render_time_ms - now_ms));
     LOG(LS_WARNING) << "A frame about to be decoded is out of the configured "
                     << "delay bounds (" << frame_delay << " > "
                     << kMaxVideoDelayMs
                     << "). Resetting the video jitter buffer.";
     return true;
   }
   if (static_cast<int>(timing_->TargetVideoDelay()) > kMaxVideoDelayMs) {
     LOG(LS_WARNING) << "The video target delay has grown larger than "
                     << kMaxVideoDelayMs << " ms.";
     return true;
   }
   return false;
 }

 void FrameBuffer::SetProtectionMode(VCMVideoProtection mode) {
   TRACE_EVENT0("webrtc", "FrameBuffer::SetProtectionMode");
   rtc::CritScope lock(&crit_);
   protection_mode_ = mode;
 }

 void FrameBuffer::Start() {
   TRACE_EVENT0("webrtc", "FrameBuffer::Start");
   rtc::CritScope lock(&crit_);
   stopped_ = false;
 }

 void FrameBuffer::Stop() {
   TRACE_EVENT0("webrtc", "FrameBuffer::Stop");
   rtc::CritScope lock(&crit_);
   stopped_ = true;
   new_continuous_frame_event_.Set();
 }

 bool FrameBuffer::ValidReferences(const FrameObject& frame) const {
   for (size_t i = 0; i < frame.num_references; ++i) {
     if (AheadOrAt(frame.references[i], frame.picture_id))
       return false;
     for (size_t j = i + 1; j < frame.num_references; ++j) {
       if (frame.references[i] == frame.references[j])
         return false;
     }
   }

   if (frame.inter_layer_predicted && frame.spatial_layer == 0)
     return false;

   return true;
 }

 void FrameBuffer::UpdatePlayoutDelays(const FrameObject& frame) {
   TRACE_EVENT0("webrtc", "FrameBuffer::UpdatePlayoutDelays");
   PlayoutDelay playout_delay = frame.EncodedImage().playout_delay_;
   if (playout_delay.min_ms >= 0)
     timing_->set_min_playout_delay(playout_delay.min_ms);

   if (playout_delay.max_ms >= 0)
     timing_->set_max_playout_delay(playout_delay.max_ms);
 }

 int FrameBuffer::InsertFrame(std::unique_ptr<FrameObject> frame) {
   TRACE_EVENT0("webrtc", "FrameBuffer::InsertFrame");
   RTC_DCHECK(frame);
   if (stats_callback_)
     stats_callback_->OnCompleteFrame(frame->num_references == 0, frame->size());
   FrameKey key(frame->picture_id, frame->spatial_layer);

   rtc::CritScope lock(&crit_);

   int last_continuous_picture_id =
       last_continuous_frame_it_ == frames_.end()
           ? -1
           : last_continuous_frame_it_->first.picture_id;

   if (!ValidReferences(*frame)) {
     LOG(LS_WARNING) << "Frame with (picture_id:spatial_id) (" << key.picture_id
                     << ":" << static_cast<int>(key.spatial_layer)
                     << ") has invalid frame references, dropping frame.";
     return last_continuous_picture_id;
   }

   if (num_frames_buffered_ >= kMaxFramesBuffered) {
     LOG(LS_WARNING) << "Frame with (picture_id:spatial_id) (" << key.picture_id
                     << ":" << static_cast<int>(key.spatial_layer)
                     << ") could not be inserted due to the frame "
                     << "buffer being full, dropping frame.";
     return last_continuous_picture_id;
   }

   if (last_decoded_frame_it_ != frames_.end() &&
       key <= last_decoded_frame_it_->first) {
     if (AheadOf(frame->timestamp, last_decoded_frame_timestamp_) &&
         frame->num_references == 0) {
       // If this frame has a newer timestamp but an earlier picture id then we
       // assume there has been a jump in the picture id due to some encoder
       // reconfiguration or some other reason. Even though this is not according
       // to spec we can still continue to decode from this frame if it is a
       // keyframe.
       LOG(LS_WARNING) << "A jump in picture id was detected, clearing buffer.";
       ClearFramesAndHistory();
       last_continuous_picture_id = -1;
     } else {
       LOG(LS_WARNING) << "Frame with (picture_id:spatial_id) ("
                       << key.picture_id << ":"
                       << static_cast<int>(key.spatial_layer)
                       << ") inserted after frame ("
                       << last_decoded_frame_it_->first.picture_id << ":"
                       << static_cast<int>(
                              last_decoded_frame_it_->first.spatial_layer)
                       << ") was handed off for decoding, dropping frame.";
       return last_continuous_picture_id;
     }
   }

   // Test if inserting this frame would cause the order of the frames to become
   // ambiguous (covering more than half the interval of 2^16). This can happen
   // when the picture id make large jumps mid stream.
   if (!frames_.empty() &&
       key < frames_.begin()->first &&
       frames_.rbegin()->first < key) {
     LOG(LS_WARNING) << "A jump in picture id was detected, clearing buffer.";
     ClearFramesAndHistory();
     last_continuous_picture_id = -1;
   }

   auto info = frames_.insert(std::make_pair(key, FrameInfo())).first;

   if (info->second.frame) {
     LOG(LS_WARNING) << "Frame with (picture_id:spatial_id) (" << key.picture_id
                     << ":" << static_cast<int>(key.spatial_layer)
                     << ") already inserted, dropping frame.";
     return last_continuous_picture_id;
   }

   if (!UpdateFrameInfoWithIncomingFrame(*frame, info))
     return last_continuous_picture_id;
   UpdatePlayoutDelays(*frame);
   info->second.frame = std::move(frame);
   ++num_frames_buffered_;

   if (info->second.num_missing_continuous == 0) {
     info->second.continuous = true;
     PropagateContinuity(info);
     last_continuous_picture_id = last_continuous_frame_it_->first.picture_id;

     // Since we now have new continuous frames there might be a better frame
     // to return from NextFrame. Signal that thread so that it again can choose
     // which frame to return.
     new_continuous_frame_event_.Set();
   }

   return last_continuous_picture_id;
 }

 void FrameBuffer::PropagateContinuity(FrameMap::iterator start) {
   TRACE_EVENT0("webrtc", "FrameBuffer::PropagateContinuity");
   RTC_DCHECK(start->second.continuous);
   if (last_continuous_frame_it_ == frames_.end())
     last_continuous_frame_it_ = start;

   std::queue<FrameMap::iterator> continuous_frames;
   continuous_frames.push(start);

   // A simple BFS to traverse continuous frames.
   while (!continuous_frames.empty()) {
     auto frame = continuous_frames.front();
     continuous_frames.pop();

     if (last_continuous_frame_it_->first < frame->first)
       last_continuous_frame_it_ = frame;

     // Loop through all dependent frames, and if that frame no longer has
     // any unfulfilled dependencies then that frame is continuous as well.
     for (size_t d = 0; d < frame->second.num_dependent_frames; ++d) {
       auto frame_ref = frames_.find(frame->second.dependent_frames[d]);
       RTC_DCHECK(frame_ref != frames_.end());

       // TODO(philipel): Look into why we've seen this happen.
       if (frame_ref != frames_.end()) {
         --frame_ref->second.num_missing_continuous;
         if (frame_ref->second.num_missing_continuous == 0) {
           frame_ref->second.continuous = true;
           continuous_frames.push(frame_ref);
         }
       }
     }
   }
 }

 void FrameBuffer::PropagateDecodability(const FrameInfo& info) {
   TRACE_EVENT0("webrtc", "FrameBuffer::PropagateDecodability");
   RTC_CHECK(info.num_dependent_frames < FrameInfo::kMaxNumDependentFrames);
   for (size_t d = 0; d < info.num_dependent_frames; ++d) {
     auto ref_info = frames_.find(info.dependent_frames[d]);
     RTC_DCHECK(ref_info != frames_.end());
     // TODO(philipel): Look into why we've seen this happen.
     if (ref_info != frames_.end()) {
       RTC_DCHECK_GT(ref_info->second.num_missing_decodable, 0U);
       --ref_info->second.num_missing_decodable;
     }
   }
 }

 void FrameBuffer::AdvanceLastDecodedFrame(FrameMap::iterator decoded) {
   TRACE_EVENT0("webrtc", "FrameBuffer::AdvanceLastDecodedFrame");
   if (last_decoded_frame_it_ == frames_.end()) {
     last_decoded_frame_it_ = frames_.begin();
   } else {
     RTC_DCHECK(last_decoded_frame_it_->first < decoded->first);
     ++last_decoded_frame_it_;
   }
   --num_frames_buffered_;
   ++num_frames_history_;

   // First, delete non-decoded frames from the history.
   while (last_decoded_frame_it_ != decoded) {
     if (last_decoded_frame_it_->second.frame)
       --num_frames_buffered_;
     last_decoded_frame_it_ = frames_.erase(last_decoded_frame_it_);
   }

   // Then remove old history if we have too much history saved.
   if (num_frames_history_ > kMaxFramesHistory) {
     frames_.erase(frames_.begin());
     --num_frames_history_;
   }
 }

 bool FrameBuffer::UpdateFrameInfoWithIncomingFrame(const FrameObject& frame,
                                                    FrameMap::iterator info) {
   TRACE_EVENT0("webrtc", "FrameBuffer::UpdateFrameInfoWithIncomingFrame");
   FrameKey key(frame.picture_id, frame.spatial_layer);
   info->second.num_missing_continuous = frame.num_references;
   info->second.num_missing_decodable = frame.num_references;

   RTC_DCHECK(last_decoded_frame_it_ == frames_.end() ||
              last_decoded_frame_it_->first < info->first);

   // Check how many dependencies that have already been fulfilled.
   for (size_t i = 0; i < frame.num_references; ++i) {
     FrameKey ref_key(frame.references[i], frame.spatial_layer);
     auto ref_info = frames_.find(ref_key);

     // Does |frame| depend on a frame earlier than the last decoded frame?
     if (last_decoded_frame_it_ != frames_.end() &&
         ref_key <= last_decoded_frame_it_->first) {
       if (ref_info == frames_.end()) {
         LOG(LS_WARNING) << "Frame with (picture_id:spatial_id) ("
                         << key.picture_id << ":"
                         << static_cast<int>(key.spatial_layer)
                         << " depends on a non-decoded frame more previous than "
                         << "the last decoded frame, dropping frame.";
         return false;
       }

       --info->second.num_missing_continuous;
       --info->second.num_missing_decodable;
     } else {
       if (ref_info == frames_.end())
         ref_info = frames_.insert(std::make_pair(ref_key, FrameInfo())).first;

       if (ref_info->second.continuous)
         --info->second.num_missing_continuous;

       // Add backwards reference so |frame| can be updated when new
       // frames are inserted or decoded.
       ref_info->second.dependent_frames[ref_info->second.num_dependent_frames] =
           key;
       RTC_DCHECK_LT(ref_info->second.num_dependent_frames,
                     (FrameInfo::kMaxNumDependentFrames - 1));
       // TODO(philipel): Look into why this could happen and handle
       // appropriately.
       if (ref_info->second.num_dependent_frames <
           (FrameInfo::kMaxNumDependentFrames - 1)) {
         ++ref_info->second.num_dependent_frames;
       }
     }
     RTC_DCHECK_LE(ref_info->second.num_missing_continuous,
                   ref_info->second.num_missing_decodable);
   }

   // Check if we have the lower spatial layer frame.
   if (frame.inter_layer_predicted) {
     ++info->second.num_missing_continuous;
     ++info->second.num_missing_decodable;

     FrameKey ref_key(frame.picture_id, frame.spatial_layer - 1);
     // Gets or create the FrameInfo for the referenced frame.
     auto ref_info = frames_.insert(std::make_pair(ref_key, FrameInfo())).first;
     if (ref_info->second.continuous)
       --info->second.num_missing_continuous;

     if (ref_info == last_decoded_frame_it_) {
       --info->second.num_missing_decodable;
     } else {
       ref_info->second.dependent_frames[ref_info->second.num_dependent_frames] =
           key;
       ++ref_info->second.num_dependent_frames;
     }
     RTC_DCHECK_LE(ref_info->second.num_missing_continuous,
                   ref_info->second.num_missing_decodable);
   }

   RTC_DCHECK_LE(info->second.num_missing_continuous,
                 info->second.num_missing_decodable);

   return true;
 }

 void FrameBuffer::UpdateJitterDelay() {
   TRACE_EVENT0("webrtc", "FrameBuffer::UpdateJitterDelay");
   if (!stats_callback_)
     return;

   int decode_ms;
   int max_decode_ms;
   int current_delay_ms;
   int target_delay_ms;
   int jitter_buffer_ms;
   int min_playout_delay_ms;
   int render_delay_ms;
   if (timing_->GetTimings(&decode_ms, &max_decode_ms, &current_delay_ms,
                           &target_delay_ms, &jitter_buffer_ms,
                           &min_playout_delay_ms, &render_delay_ms)) {
     stats_callback_->OnFrameBufferTimingsUpdated(
         decode_ms, max_decode_ms, current_delay_ms, target_delay_ms,
         jitter_buffer_ms, min_playout_delay_ms, render_delay_ms);
   }
 }

 void FrameBuffer::UpdateTimingFrameInfo() {
   TRACE_EVENT0("webrtc", "FrameBuffer::UpdateTimingFrameInfo");
   rtc::Optional<TimingFrameInfo> info = timing_->GetTimingFrameInfo();
   if (info)
     stats_callback_->OnTimingFrameInfoUpdated(*info);
 }

 void FrameBuffer::ClearFramesAndHistory() {
   TRACE_EVENT0("webrtc", "FrameBuffer::ClearFramesAndHistory");
   frames_.clear();
   last_decoded_frame_it_ = frames_.end();
   last_continuous_frame_it_ = frames_.end();
   next_frame_it_ = frames_.end();
   num_frames_history_ = 0;
   num_frames_buffered_ = 0;
 }

 }  // namespace video_coding
 }  // namespace webrtc
	/*
	* Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
	*
	* Use of this source code is governed by a BSD-style license
	* that can be found in the LICENSE file in the root of the source
	* tree. An additional intellectual property rights grant can be found
	* in the file PATENTS. All contributing project authors may
	* be found in the AUTHORS file in the root of the source tree.
	*/

	#include "webrtc/modules/video_coding/frame_buffer2.h"

	#include <algorithm>
	#include <cstring>
	#include <queue>

	#include "webrtc/modules/video_coding/include/video_coding_defines.h"
	#include "webrtc/modules/video_coding/jitter_estimator.h"
	#include "webrtc/modules/video_coding/timing.h"
	#include "webrtc/rtc_base/checks.h"
	#include "webrtc/rtc_base/logging.h"
	#include "webrtc/rtc_base/trace_event.h"
	#include "webrtc/system_wrappers/include/clock.h"
	#include "webrtc/system_wrappers/include/metrics.h"

	namespace webrtc {
	namespace video_coding {

	namespace {
	// Max number of frames the buffer will hold.
	constexpr int kMaxFramesBuffered = 600;

	// Max number of decoded frame info that will be saved.
	constexpr int kMaxFramesHistory = 50;
	} // namespace

	FrameBuffer::FrameBuffer(Clock* clock,
	VCMJitterEstimator* jitter_estimator,
	VCMTiming* timing,
	VCMReceiveStatisticsCallback* stats_callback)
	: clock_(clock),
	new_continuous_frame_event_(false, false),
	jitter_estimator_(jitter_estimator),
	timing_(timing),
	inter_frame_delay_(clock_->TimeInMilliseconds()),
	last_decoded_frame_timestamp_(0),
	last_decoded_frame_it_(frames_.end()),
	last_continuous_frame_it_(frames_.end()),
	num_frames_history_(0),
	num_frames_buffered_(0),
	stopped_(false),
	protection_mode_(kProtectionNack),
	stats_callback_(stats_callback) {}

	FrameBuffer::~FrameBuffer() {}

	FrameBuffer::ReturnReason FrameBuffer::NextFrame(
	int64_t max_wait_time_ms,
	std::unique_ptr<FrameObject>* frame_out) {
	TRACE_EVENT0("webrtc", "FrameBuffer::NextFrame");
	int64_t latest_return_time_ms =
	clock_->TimeInMilliseconds() + max_wait_time_ms;
	int64_t wait_ms = max_wait_time_ms;
	int64_t now_ms = 0;

	do {
	now_ms = clock_->TimeInMilliseconds();
	{
	rtc::CritScope lock(&crit_);
	new_continuous_frame_event_.Reset();
	if (stopped_)
	return kStopped;

	wait_ms = max_wait_time_ms;

	// Need to hold \|crit_\| in order to use \|frames_\|, therefore we
	// set it here in the loop instead of outside the loop in order to not
	// acquire the lock unnecesserily.
	next_frame_it_ = frames_.end();

	// \|frame_it\| points to the first frame after the
	// \|last_decoded_frame_it_\|.
	auto frame_it = frames_.end();
	if (last_decoded_frame_it_ == frames_.end()) {
	frame_it = frames_.begin();
	} else {
	frame_it = last_decoded_frame_it_;
	++frame_it;
	}

	// \|continuous_end_it\| points to the first frame after the
	// \|last_continuous_frame_it_\|.
	auto continuous_end_it = last_continuous_frame_it_;
	if (continuous_end_it != frames_.end())
	++continuous_end_it;

	for (; frame_it != continuous_end_it && frame_it != frames_.end();
	++frame_it) {
	if (!frame_it->second.continuous \|\|
	frame_it->second.num_missing_decodable > 0) {
	continue;
	}

	FrameObject* frame = frame_it->second.frame.get();
	next_frame_it_ = frame_it;
	if (frame->RenderTime() == -1)
	frame->SetRenderTime(timing_->RenderTimeMs(frame->timestamp, now_ms));
	wait_ms = timing_->MaxWaitingTime(frame->RenderTime(), now_ms);

	// This will cause the frame buffer to prefer high framerate rather
	// than high resolution in the case of the decoder not decoding fast
	// enough and the stream has multiple spatial and temporal layers.
	if (wait_ms == 0)
	continue;

	break;
	}
	} // rtc::Critscope lock(&crit_);

	wait_ms = std::min<int64_t>(wait_ms, latest_return_time_ms - now_ms);
	wait_ms = std::max<int64_t>(wait_ms, 0);
	} while (new_continuous_frame_event_.Wait(wait_ms));

	{
	rtc::CritScope lock(&crit_);
	now_ms = clock_->TimeInMilliseconds();
	if (next_frame_it_ != frames_.end()) {
	std::unique_ptr<FrameObject> frame =
	std::move(next_frame_it_->second.frame);

	if (!frame->delayed_by_retransmission()) {
	int64_t frame_delay;

	if (inter_frame_delay_.CalculateDelay(frame->timestamp, &frame_delay,
	frame->ReceivedTime())) {
	jitter_estimator_->UpdateEstimate(frame_delay, frame->size());
	}

	float rtt_mult = protection_mode_ == kProtectionNackFEC ? 0.0 : 1.0;
	timing_->SetJitterDelay(jitter_estimator_->GetJitterEstimate(rtt_mult));
	timing_->UpdateCurrentDelay(frame->RenderTime(), now_ms);
	}

	// Gracefully handle bad RTP timestamps and render time issues.
	if (HasBadRenderTiming(*frame, now_ms)) {
	jitter_estimator_->Reset();
	timing_->Reset();
	frame->SetRenderTime(timing_->RenderTimeMs(frame->timestamp, now_ms));
	}

	UpdateJitterDelay();
	UpdateTimingFrameInfo();
	PropagateDecodability(next_frame_it_->second);

	// Sanity check for RTP timestamp monotonicity.
	if (last_decoded_frame_it_ != frames_.end()) {
	const FrameKey& last_decoded_frame_key = last_decoded_frame_it_->first;
	const FrameKey& frame_key = next_frame_it_->first;

	const bool frame_is_higher_spatial_layer_of_last_decoded_frame =
	last_decoded_frame_timestamp_ == frame->timestamp &&
	last_decoded_frame_key.picture_id == frame_key.picture_id &&
	last_decoded_frame_key.spatial_layer < frame_key.spatial_layer;

	if (AheadOrAt(last_decoded_frame_timestamp_, frame->timestamp) &&
	!frame_is_higher_spatial_layer_of_last_decoded_frame) {
	// TODO(brandtr): Consider clearing the entire buffer when we hit
	// these conditions.
	LOG(LS_WARNING) << "Frame with (timestamp:picture_id:spatial_id) ("
	<< frame->timestamp << ":" << frame->picture_id << ":"
	<< static_cast<int>(frame->spatial_layer) << ")"
	<< " sent to decoder after frame with"
	<< " (timestamp:picture_id:spatial_id) ("
	<< last_decoded_frame_timestamp_ << ":"
	<< last_decoded_frame_key.picture_id << ":"
	<< static_cast<int>(
	last_decoded_frame_key.spatial_layer)
	<< ").";
	}
	}

	AdvanceLastDecodedFrame(next_frame_it_);
	last_decoded_frame_timestamp_ = frame->timestamp;
	*frame_out = std::move(frame);
	return kFrameFound;
	}
	}

	if (latest_return_time_ms - now_ms > 0) {
	// If \|next_frame_it_ == frames_.end()\| and there is still time left, it
	// means that the frame buffer was cleared as the thread in this function
	// was waiting to acquire \|crit_\| in order to return. Wait for the
	// remaining time and then return.
	return NextFrame(latest_return_time_ms - now_ms, frame_out);
	}

	return kTimeout;
	}

	bool FrameBuffer::HasBadRenderTiming(const FrameObject& frame, int64_t now_ms) {
	// Assume that render timing errors are due to changes in the video stream.
	int64_t render_time_ms = frame.RenderTimeMs();
	const int64_t kMaxVideoDelayMs = 10000;
	if (render_time_ms < 0) {
	return true;
	}
	if (std::abs(render_time_ms - now_ms) > kMaxVideoDelayMs) {
	int frame_delay = static_cast<int>(std::abs(render_time_ms - now_ms));
	LOG(LS_WARNING) << "A frame about to be decoded is out of the configured "
	<< "delay bounds (" << frame_delay << " > "
	<< kMaxVideoDelayMs
	<< "). Resetting the video jitter buffer.";
	return true;
	}
	if (static_cast<int>(timing_->TargetVideoDelay()) > kMaxVideoDelayMs) {
	LOG(LS_WARNING) << "The video target delay has grown larger than "
	<< kMaxVideoDelayMs << " ms.";
	return true;
	}
	return false;
	}

	void FrameBuffer::SetProtectionMode(VCMVideoProtection mode) {
	TRACE_EVENT0("webrtc", "FrameBuffer::SetProtectionMode");
	rtc::CritScope lock(&crit_);
	protection_mode_ = mode;
	}

	void FrameBuffer::Start() {
	TRACE_EVENT0("webrtc", "FrameBuffer::Start");
	rtc::CritScope lock(&crit_);
	stopped_ = false;
	}

	void FrameBuffer::Stop() {
	TRACE_EVENT0("webrtc", "FrameBuffer::Stop");
	rtc::CritScope lock(&crit_);
	stopped_ = true;
	new_continuous_frame_event_.Set();
	}

	bool FrameBuffer::ValidReferences(const FrameObject& frame) const {
	for (size_t i = 0; i < frame.num_references; ++i) {
	if (AheadOrAt(frame.references[i], frame.picture_id))
	return false;
	for (size_t j = i + 1; j < frame.num_references; ++j) {
	if (frame.references[i] == frame.references[j])
	return false;
	}
	}

	if (frame.inter_layer_predicted && frame.spatial_layer == 0)
	return false;

	return true;
	}

	void FrameBuffer::UpdatePlayoutDelays(const FrameObject& frame) {
	TRACE_EVENT0("webrtc", "FrameBuffer::UpdatePlayoutDelays");
	PlayoutDelay playout_delay = frame.EncodedImage().playout_delay_;
	if (playout_delay.min_ms >= 0)
	timing_->set_min_playout_delay(playout_delay.min_ms);

	if (playout_delay.max_ms >= 0)
	timing_->set_max_playout_delay(playout_delay.max_ms);
	}

	int FrameBuffer::InsertFrame(std::unique_ptr<FrameObject> frame) {
	TRACE_EVENT0("webrtc", "FrameBuffer::InsertFrame");
	RTC_DCHECK(frame);
	if (stats_callback_)
	stats_callback_->OnCompleteFrame(frame->num_references == 0, frame->size());
	FrameKey key(frame->picture_id, frame->spatial_layer);

	rtc::CritScope lock(&crit_);

	int last_continuous_picture_id =
	last_continuous_frame_it_ == frames_.end()
	? -1
	: last_continuous_frame_it_->first.picture_id;

	if (!ValidReferences(*frame)) {
	LOG(LS_WARNING) << "Frame with (picture_id:spatial_id) (" << key.picture_id
	<< ":" << static_cast<int>(key.spatial_layer)
	<< ") has invalid frame references, dropping frame.";
	return last_continuous_picture_id;
	}

	if (num_frames_buffered_ >= kMaxFramesBuffered) {
	LOG(LS_WARNING) << "Frame with (picture_id:spatial_id) (" << key.picture_id
	<< ":" << static_cast<int>(key.spatial_layer)
	<< ") could not be inserted due to the frame "
	<< "buffer being full, dropping frame.";
	return last_continuous_picture_id;
	}

	if (last_decoded_frame_it_ != frames_.end() &&
	key <= last_decoded_frame_it_->first) {
	if (AheadOf(frame->timestamp, last_decoded_frame_timestamp_) &&
	frame->num_references == 0) {
	// If this frame has a newer timestamp but an earlier picture id then we
	// assume there has been a jump in the picture id due to some encoder
	// reconfiguration or some other reason. Even though this is not according
	// to spec we can still continue to decode from this frame if it is a
	// keyframe.
	LOG(LS_WARNING) << "A jump in picture id was detected, clearing buffer.";
	ClearFramesAndHistory();
	last_continuous_picture_id = -1;
	} else {
	LOG(LS_WARNING) << "Frame with (picture_id:spatial_id) ("
	<< key.picture_id << ":"
	<< static_cast<int>(key.spatial_layer)
	<< ") inserted after frame ("
	<< last_decoded_frame_it_->first.picture_id << ":"
	<< static_cast<int>(
	last_decoded_frame_it_->first.spatial_layer)
	<< ") was handed off for decoding, dropping frame.";
	return last_continuous_picture_id;
	}
	}

	// Test if inserting this frame would cause the order of the frames to become
	// ambiguous (covering more than half the interval of 2^16). This can happen
	// when the picture id make large jumps mid stream.
	if (!frames_.empty() &&
	key < frames_.begin()->first &&
	frames_.rbegin()->first < key) {
	LOG(LS_WARNING) << "A jump in picture id was detected, clearing buffer.";
	ClearFramesAndHistory();
	last_continuous_picture_id = -1;
	}

	auto info = frames_.insert(std::make_pair(key, FrameInfo())).first;

	if (info->second.frame) {
	LOG(LS_WARNING) << "Frame with (picture_id:spatial_id) (" << key.picture_id
	<< ":" << static_cast<int>(key.spatial_layer)
	<< ") already inserted, dropping frame.";
	return last_continuous_picture_id;
	}

	if (!UpdateFrameInfoWithIncomingFrame(*frame, info))
	return last_continuous_picture_id;
	UpdatePlayoutDelays(*frame);
	info->second.frame = std::move(frame);
	++num_frames_buffered_;

	if (info->second.num_missing_continuous == 0) {
	info->second.continuous = true;
	PropagateContinuity(info);
	last_continuous_picture_id = last_continuous_frame_it_->first.picture_id;

	// Since we now have new continuous frames there might be a better frame
	// to return from NextFrame. Signal that thread so that it again can choose
	// which frame to return.
	new_continuous_frame_event_.Set();
	}

	return last_continuous_picture_id;
	}

	void FrameBuffer::PropagateContinuity(FrameMap::iterator start) {
	TRACE_EVENT0("webrtc", "FrameBuffer::PropagateContinuity");
	RTC_DCHECK(start->second.continuous);
	if (last_continuous_frame_it_ == frames_.end())
	last_continuous_frame_it_ = start;

	std::queue<FrameMap::iterator> continuous_frames;
	continuous_frames.push(start);

	// A simple BFS to traverse continuous frames.
	while (!continuous_frames.empty()) {
	auto frame = continuous_frames.front();
	continuous_frames.pop();

	if (last_continuous_frame_it_->first < frame->first)
	last_continuous_frame_it_ = frame;

	// Loop through all dependent frames, and if that frame no longer has
	// any unfulfilled dependencies then that frame is continuous as well.
	for (size_t d = 0; d < frame->second.num_dependent_frames; ++d) {
	auto frame_ref = frames_.find(frame->second.dependent_frames[d]);
	RTC_DCHECK(frame_ref != frames_.end());

	// TODO(philipel): Look into why we've seen this happen.
	if (frame_ref != frames_.end()) {
	--frame_ref->second.num_missing_continuous;
	if (frame_ref->second.num_missing_continuous == 0) {
	frame_ref->second.continuous = true;
	continuous_frames.push(frame_ref);
	}
	}
	}
	}
	}

	void FrameBuffer::PropagateDecodability(const FrameInfo& info) {
	TRACE_EVENT0("webrtc", "FrameBuffer::PropagateDecodability");
	RTC_CHECK(info.num_dependent_frames < FrameInfo::kMaxNumDependentFrames);
	for (size_t d = 0; d < info.num_dependent_frames; ++d) {
	auto ref_info = frames_.find(info.dependent_frames[d]);
	RTC_DCHECK(ref_info != frames_.end());
	// TODO(philipel): Look into why we've seen this happen.
	if (ref_info != frames_.end()) {
	RTC_DCHECK_GT(ref_info->second.num_missing_decodable, 0U);
	--ref_info->second.num_missing_decodable;
	}
	}
	}

	void FrameBuffer::AdvanceLastDecodedFrame(FrameMap::iterator decoded) {
	TRACE_EVENT0("webrtc", "FrameBuffer::AdvanceLastDecodedFrame");
	if (last_decoded_frame_it_ == frames_.end()) {
	last_decoded_frame_it_ = frames_.begin();
	} else {
	RTC_DCHECK(last_decoded_frame_it_->first < decoded->first);
	++last_decoded_frame_it_;
	}
	--num_frames_buffered_;
	++num_frames_history_;

	// First, delete non-decoded frames from the history.
	while (last_decoded_frame_it_ != decoded) {
	if (last_decoded_frame_it_->second.frame)
	--num_frames_buffered_;
	last_decoded_frame_it_ = frames_.erase(last_decoded_frame_it_);
	}

	// Then remove old history if we have too much history saved.
	if (num_frames_history_ > kMaxFramesHistory) {
	frames_.erase(frames_.begin());
	--num_frames_history_;
	}
	}

	bool FrameBuffer::UpdateFrameInfoWithIncomingFrame(const FrameObject& frame,
	FrameMap::iterator info) {
	TRACE_EVENT0("webrtc", "FrameBuffer::UpdateFrameInfoWithIncomingFrame");
	FrameKey key(frame.picture_id, frame.spatial_layer);
	info->second.num_missing_continuous = frame.num_references;
	info->second.num_missing_decodable = frame.num_references;

	RTC_DCHECK(last_decoded_frame_it_ == frames_.end() \|\|
	last_decoded_frame_it_->first < info->first);

	// Check how many dependencies that have already been fulfilled.
	for (size_t i = 0; i < frame.num_references; ++i) {
	FrameKey ref_key(frame.references[i], frame.spatial_layer);
	auto ref_info = frames_.find(ref_key);

	// Does \|frame\| depend on a frame earlier than the last decoded frame?
	if (last_decoded_frame_it_ != frames_.end() &&
	ref_key <= last_decoded_frame_it_->first) {
	if (ref_info == frames_.end()) {
	LOG(LS_WARNING) << "Frame with (picture_id:spatial_id) ("
	<< key.picture_id << ":"
	<< static_cast<int>(key.spatial_layer)
	<< " depends on a non-decoded frame more previous than "
	<< "the last decoded frame, dropping frame.";
	return false;
	}

	--info->second.num_missing_continuous;
	--info->second.num_missing_decodable;
	} else {
	if (ref_info == frames_.end())
	ref_info = frames_.insert(std::make_pair(ref_key, FrameInfo())).first;

	if (ref_info->second.continuous)
	--info->second.num_missing_continuous;

	// Add backwards reference so \|frame\| can be updated when new
	// frames are inserted or decoded.
	ref_info->second.dependent_frames[ref_info->second.num_dependent_frames] =
	key;
	RTC_DCHECK_LT(ref_info->second.num_dependent_frames,
	(FrameInfo::kMaxNumDependentFrames - 1));
	// TODO(philipel): Look into why this could happen and handle
	// appropriately.
	if (ref_info->second.num_dependent_frames <
	(FrameInfo::kMaxNumDependentFrames - 1)) {
	++ref_info->second.num_dependent_frames;
	}
	}
	RTC_DCHECK_LE(ref_info->second.num_missing_continuous,
	ref_info->second.num_missing_decodable);
	}

	// Check if we have the lower spatial layer frame.
	if (frame.inter_layer_predicted) {
	++info->second.num_missing_continuous;
	++info->second.num_missing_decodable;

	FrameKey ref_key(frame.picture_id, frame.spatial_layer - 1);
	// Gets or create the FrameInfo for the referenced frame.
	auto ref_info = frames_.insert(std::make_pair(ref_key, FrameInfo())).first;
	if (ref_info->second.continuous)
	--info->second.num_missing_continuous;

	if (ref_info == last_decoded_frame_it_) {
	--info->second.num_missing_decodable;
	} else {
	ref_info->second.dependent_frames[ref_info->second.num_dependent_frames] =
	key;
	++ref_info->second.num_dependent_frames;
	}
	RTC_DCHECK_LE(ref_info->second.num_missing_continuous,
	ref_info->second.num_missing_decodable);
	}

	RTC_DCHECK_LE(info->second.num_missing_continuous,
	info->second.num_missing_decodable);

	return true;
	}

	void FrameBuffer::UpdateJitterDelay() {
	TRACE_EVENT0("webrtc", "FrameBuffer::UpdateJitterDelay");
	if (!stats_callback_)
	return;

	int decode_ms;
	int max_decode_ms;
	int current_delay_ms;
	int target_delay_ms;
	int jitter_buffer_ms;
	int min_playout_delay_ms;
	int render_delay_ms;
	if (timing_->GetTimings(&decode_ms, &max_decode_ms, &current_delay_ms,
	&target_delay_ms, &jitter_buffer_ms,
	&min_playout_delay_ms, &render_delay_ms)) {
	stats_callback_->OnFrameBufferTimingsUpdated(
	decode_ms, max_decode_ms, current_delay_ms, target_delay_ms,
	jitter_buffer_ms, min_playout_delay_ms, render_delay_ms);
	}
	}

	void FrameBuffer::UpdateTimingFrameInfo() {
	TRACE_EVENT0("webrtc", "FrameBuffer::UpdateTimingFrameInfo");
	rtc::Optional<TimingFrameInfo> info = timing_->GetTimingFrameInfo();
	if (info)
	stats_callback_->OnTimingFrameInfoUpdated(*info);
	}

	void FrameBuffer::ClearFramesAndHistory() {
	TRACE_EVENT0("webrtc", "FrameBuffer::ClearFramesAndHistory");
	frames_.clear();
	last_decoded_frame_it_ = frames_.end();
	last_continuous_frame_it_ = frames_.end();
	next_frame_it_ = frames_.end();
	num_frames_history_ = 0;
	num_frames_buffered_ = 0;
	}

	} // namespace video_coding
	} // namespace webrtc