webrtc/modules/video_coding/packet_buffer.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/packet_buffer.h"

 #include <algorithm>
 #include <limits>
 #include <utility>

 #include "webrtc/common_video/h264/h264_common.h"
 #include "webrtc/modules/video_coding/frame_object.h"
 #include "webrtc/rtc_base/atomicops.h"
 #include "webrtc/rtc_base/checks.h"
 #include "webrtc/rtc_base/logging.h"
 #include "webrtc/system_wrappers/include/clock.h"

 namespace webrtc {
 namespace video_coding {

 rtc::scoped_refptr<PacketBuffer> PacketBuffer::Create(
     Clock* clock,
     size_t start_buffer_size,
     size_t max_buffer_size,
     OnReceivedFrameCallback* received_frame_callback) {
   return rtc::scoped_refptr<PacketBuffer>(new PacketBuffer(
       clock, start_buffer_size, max_buffer_size, received_frame_callback));
 }

 PacketBuffer::PacketBuffer(Clock* clock,
                            size_t start_buffer_size,
                            size_t max_buffer_size,
                            OnReceivedFrameCallback* received_frame_callback)
     : clock_(clock),
       size_(start_buffer_size),
       max_size_(max_buffer_size),
       first_seq_num_(0),
       first_packet_received_(false),
       is_cleared_to_first_seq_num_(false),
       data_buffer_(start_buffer_size),
       sequence_buffer_(start_buffer_size),
       received_frame_callback_(received_frame_callback) {
   RTC_DCHECK_LE(start_buffer_size, max_buffer_size);
   // Buffer size must always be a power of 2.
   RTC_DCHECK((start_buffer_size & (start_buffer_size - 1)) == 0);
   RTC_DCHECK((max_buffer_size & (max_buffer_size - 1)) == 0);
 }

 PacketBuffer::~PacketBuffer() {
   Clear();
 }

 bool PacketBuffer::InsertPacket(VCMPacket* packet) {
   std::vector<std::unique_ptr<RtpFrameObject>> found_frames;
   {
     rtc::CritScope lock(&crit_);

     uint16_t seq_num = packet->seqNum;
     size_t index = seq_num % size_;

     if (!first_packet_received_) {
       first_seq_num_ = seq_num;
       first_packet_received_ = true;
     } else if (AheadOf(first_seq_num_, seq_num)) {
       // If we have explicitly cleared past this packet then it's old,
       // don't insert it.
       if (is_cleared_to_first_seq_num_) {
         delete[] packet->dataPtr;
         packet->dataPtr = nullptr;
         return false;
       }

       first_seq_num_ = seq_num;
     }

     if (sequence_buffer_[index].used) {
       // Duplicate packet, just delete the payload.
       if (data_buffer_[index].seqNum == packet->seqNum) {
         delete[] packet->dataPtr;
         packet->dataPtr = nullptr;
         return true;
       }

       // The packet buffer is full, try to expand the buffer.
       while (ExpandBufferSize() && sequence_buffer_[seq_num % size_].used) {
       }
       index = seq_num % size_;

       // Packet buffer is still full.
       if (sequence_buffer_[index].used) {
         delete[] packet->dataPtr;
         packet->dataPtr = nullptr;
         return false;
       }
     }

     sequence_buffer_[index].frame_begin = packet->is_first_packet_in_frame;
     sequence_buffer_[index].frame_end = packet->markerBit;
     sequence_buffer_[index].seq_num = packet->seqNum;
     sequence_buffer_[index].continuous = false;
     sequence_buffer_[index].frame_created = false;
     sequence_buffer_[index].used = true;
     data_buffer_[index] = *packet;
     packet->dataPtr = nullptr;

     UpdateMissingPackets(packet->seqNum);

     int64_t now_ms = clock_->TimeInMilliseconds();
     last_received_packet_ms_ = rtc::Optional<int64_t>(now_ms);
     if (packet->frameType == kVideoFrameKey)
       last_received_keyframe_packet_ms_ = rtc::Optional<int64_t>(now_ms);

     found_frames = FindFrames(seq_num);
   }

   for (std::unique_ptr<RtpFrameObject>& frame : found_frames)
     received_frame_callback_->OnReceivedFrame(std::move(frame));

   return true;
 }

 void PacketBuffer::ClearTo(uint16_t seq_num) {
   rtc::CritScope lock(&crit_);

   // If the packet buffer was cleared between a frame was created and returned.
   if (!first_packet_received_)
     return;

   is_cleared_to_first_seq_num_ = true;
   while (AheadOrAt<uint16_t>(seq_num, first_seq_num_)) {
     size_t index = first_seq_num_ % size_;
     delete[] data_buffer_[index].dataPtr;
     data_buffer_[index].dataPtr = nullptr;
     sequence_buffer_[index].used = false;
     ++first_seq_num_;
   }

   missing_packets_.erase(missing_packets_.begin(),
                          missing_packets_.upper_bound(seq_num));
 }

 void PacketBuffer::Clear() {
   rtc::CritScope lock(&crit_);
   for (size_t i = 0; i < size_; ++i) {
     delete[] data_buffer_[i].dataPtr;
     data_buffer_[i].dataPtr = nullptr;
     sequence_buffer_[i].used = false;
   }

   first_packet_received_ = false;
   is_cleared_to_first_seq_num_ = false;
   last_received_packet_ms_.reset();
   last_received_keyframe_packet_ms_.reset();
   newest_inserted_seq_num_.reset();
   missing_packets_.clear();
 }

 void PacketBuffer::PaddingReceived(uint16_t seq_num) {
   std::vector<std::unique_ptr<RtpFrameObject>> found_frames;
   {
     rtc::CritScope lock(&crit_);
     UpdateMissingPackets(seq_num);
     found_frames = FindFrames(static_cast<uint16_t>(seq_num + 1));
   }

   for (std::unique_ptr<RtpFrameObject>& frame : found_frames)
     received_frame_callback_->OnReceivedFrame(std::move(frame));
 }

 rtc::Optional<int64_t> PacketBuffer::LastReceivedPacketMs() const {
   rtc::CritScope lock(&crit_);
   return last_received_packet_ms_;
 }

 rtc::Optional<int64_t> PacketBuffer::LastReceivedKeyframePacketMs() const {
   rtc::CritScope lock(&crit_);
   return last_received_keyframe_packet_ms_;
 }

 bool PacketBuffer::ExpandBufferSize() {
   if (size_ == max_size_) {
     LOG(LS_WARNING) << "PacketBuffer is already at max size (" << max_size_
                     << "), failed to increase size. Clearing PacketBuffer.";
     Clear();
     return false;
   }

   size_t new_size = std::min(max_size_, 2 * size_);
   std::vector<VCMPacket> new_data_buffer(new_size);
   std::vector<ContinuityInfo> new_sequence_buffer(new_size);
   for (size_t i = 0; i < size_; ++i) {
     if (sequence_buffer_[i].used) {
       size_t index = sequence_buffer_[i].seq_num % new_size;
       new_sequence_buffer[index] = sequence_buffer_[i];
       new_data_buffer[index] = data_buffer_[i];
     }
   }
   size_ = new_size;
   sequence_buffer_ = std::move(new_sequence_buffer);
   data_buffer_ = std::move(new_data_buffer);
   LOG(LS_INFO) << "PacketBuffer size expanded to " << new_size;
   return true;
 }

 bool PacketBuffer::PotentialNewFrame(uint16_t seq_num) const {
   size_t index = seq_num % size_;
   int prev_index = index > 0 ? index - 1 : size_ - 1;

   if (!sequence_buffer_[index].used)
     return false;
   if (sequence_buffer_[index].seq_num != seq_num)
     return false;
   if (sequence_buffer_[index].frame_created)
     return false;
   if (sequence_buffer_[index].frame_begin)
     return true;
   if (!sequence_buffer_[prev_index].used)
     return false;
   if (sequence_buffer_[prev_index].frame_created)
     return false;
   if (sequence_buffer_[prev_index].seq_num !=
       static_cast<uint16_t>(sequence_buffer_[index].seq_num - 1)) {
     return false;
   }
   if (sequence_buffer_[prev_index].continuous)
     return true;

   return false;
 }

 std::vector<std::unique_ptr<RtpFrameObject>> PacketBuffer::FindFrames(
     uint16_t seq_num) {
   std::vector<std::unique_ptr<RtpFrameObject>> found_frames;
   for (size_t i = 0; i < size_ && PotentialNewFrame(seq_num); ++i) {
     size_t index = seq_num % size_;
     sequence_buffer_[index].continuous = true;

     // If all packets of the frame is continuous, find the first packet of the
     // frame and create an RtpFrameObject.
     if (sequence_buffer_[index].frame_end) {
       size_t frame_size = 0;
       int max_nack_count = -1;
       uint16_t start_seq_num = seq_num;

       // Find the start index by searching backward until the packet with
       // the |frame_begin| flag is set.
       int start_index = index;

       bool is_h264 = data_buffer_[start_index].codec == kVideoCodecH264;
       bool is_h264_keyframe = false;
       int64_t frame_timestamp = data_buffer_[start_index].timestamp;

       // Since packet at |data_buffer_[index]| is already part of the frame
       // we will have at most |size_ - 1| packets left to check.
       for (size_t j = 0; j < size_ - 1; ++j) {
         frame_size += data_buffer_[start_index].sizeBytes;
         max_nack_count =
             std::max(max_nack_count, data_buffer_[start_index].timesNacked);
         sequence_buffer_[start_index].frame_created = true;

         if (!is_h264 && sequence_buffer_[start_index].frame_begin)
           break;

         if (is_h264 && !is_h264_keyframe) {
           const RTPVideoHeaderH264& header =
               data_buffer_[start_index].video_header.codecHeader.H264;
           for (size_t i = 0; i < header.nalus_length; ++i) {
             if (header.nalus[i].type == H264::NaluType::kIdr) {
               is_h264_keyframe = true;
               break;
             }
           }
         }

         start_index = start_index > 0 ? start_index - 1 : size_ - 1;

         // In the case of H264 we don't have a frame_begin bit (yes,
         // |frame_begin| might be set to true but that is a lie). So instead
         // we traverese backwards as long as we have a previous packet and
         // the timestamp of that packet is the same as this one. This may cause
         // the PacketBuffer to hand out incomplete frames.
         // See: https://bugs.chromium.org/p/webrtc/issues/detail?id=7106
         if (is_h264 &&
             (!sequence_buffer_[start_index].used ||
              data_buffer_[start_index].timestamp != frame_timestamp)) {
           break;
         }

         --start_seq_num;
       }

       // If this is H264 but not a keyframe, make sure there are no gaps in the
       // packet sequence numbers up until this point.
       if (is_h264 && !is_h264_keyframe &&
           missing_packets_.upper_bound(start_seq_num) !=
               missing_packets_.begin()) {
         uint16_t stop_index = (index + 1) % size_;
         while (start_index != stop_index) {
           sequence_buffer_[start_index].frame_created = false;
           start_index = (start_index + 1) % size_;
         }

         return found_frames;
       }

       missing_packets_.erase(missing_packets_.begin(),
                              missing_packets_.upper_bound(seq_num));

       found_frames.emplace_back(
           new RtpFrameObject(this, start_seq_num, seq_num, frame_size,
                              max_nack_count, clock_->TimeInMilliseconds()));
     }
     ++seq_num;
   }
   return found_frames;
 }

 void PacketBuffer::ReturnFrame(RtpFrameObject* frame) {
   rtc::CritScope lock(&crit_);
   size_t index = frame->first_seq_num() % size_;
   size_t end = (frame->last_seq_num() + 1) % size_;
   uint16_t seq_num = frame->first_seq_num();
   while (index != end) {
     if (sequence_buffer_[index].seq_num == seq_num) {
       delete[] data_buffer_[index].dataPtr;
       data_buffer_[index].dataPtr = nullptr;
       sequence_buffer_[index].used = false;
     }

     index = (index + 1) % size_;
     ++seq_num;
   }
 }

 bool PacketBuffer::GetBitstream(const RtpFrameObject& frame,
                                 uint8_t* destination) {
   rtc::CritScope lock(&crit_);

   size_t index = frame.first_seq_num() % size_;
   size_t end = (frame.last_seq_num() + 1) % size_;
   uint16_t seq_num = frame.first_seq_num();
   while (index != end) {
     if (!sequence_buffer_[index].used ||
         sequence_buffer_[index].seq_num != seq_num) {
       return false;
     }

     const uint8_t* source = data_buffer_[index].dataPtr;
     size_t length = data_buffer_[index].sizeBytes;
     memcpy(destination, source, length);
     destination += length;
     index = (index + 1) % size_;
     ++seq_num;
   }
   return true;
 }

 VCMPacket* PacketBuffer::GetPacket(uint16_t seq_num) {
   size_t index = seq_num % size_;
   if (!sequence_buffer_[index].used ||
       seq_num != sequence_buffer_[index].seq_num) {
     return nullptr;
   }
   return &data_buffer_[index];
 }

 int PacketBuffer::AddRef() const {
   return rtc::AtomicOps::Increment(&ref_count_);
 }

 int PacketBuffer::Release() const {
   int count = rtc::AtomicOps::Decrement(&ref_count_);
   if (!count) {
     delete this;
   }
   return count;
 }

 void PacketBuffer::UpdateMissingPackets(uint16_t seq_num) {
   if (!newest_inserted_seq_num_)
     newest_inserted_seq_num_ = rtc::Optional<uint16_t>(seq_num);

   const int kMaxPaddingAge = 1000;
   if (AheadOf(seq_num, *newest_inserted_seq_num_)) {
     uint16_t old_seq_num = seq_num - kMaxPaddingAge;
     auto erase_to = missing_packets_.lower_bound(old_seq_num);
     missing_packets_.erase(missing_packets_.begin(), erase_to);

     // Guard against inserting a large amount of missing packets if there is a
     // jump in the sequence number.
     if (AheadOf(old_seq_num, *newest_inserted_seq_num_))
       *newest_inserted_seq_num_ = old_seq_num;

     ++*newest_inserted_seq_num_;
     while (AheadOf(seq_num, *newest_inserted_seq_num_)) {
       missing_packets_.insert(*newest_inserted_seq_num_);
       ++*newest_inserted_seq_num_;
     }
   } else {
     missing_packets_.erase(seq_num);
   }
 }

 }  // 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/packet_buffer.h"

	#include <algorithm>
	#include <limits>
	#include <utility>

	#include "webrtc/common_video/h264/h264_common.h"
	#include "webrtc/modules/video_coding/frame_object.h"
	#include "webrtc/rtc_base/atomicops.h"
	#include "webrtc/rtc_base/checks.h"
	#include "webrtc/rtc_base/logging.h"
	#include "webrtc/system_wrappers/include/clock.h"

	namespace webrtc {
	namespace video_coding {

	rtc::scoped_refptr<PacketBuffer> PacketBuffer::Create(
	Clock* clock,
	size_t start_buffer_size,
	size_t max_buffer_size,
	OnReceivedFrameCallback* received_frame_callback) {
	return rtc::scoped_refptr<PacketBuffer>(new PacketBuffer(
	clock, start_buffer_size, max_buffer_size, received_frame_callback));
	}

	PacketBuffer::PacketBuffer(Clock* clock,
	size_t start_buffer_size,
	size_t max_buffer_size,
	OnReceivedFrameCallback* received_frame_callback)
	: clock_(clock),
	size_(start_buffer_size),
	max_size_(max_buffer_size),
	first_seq_num_(0),
	first_packet_received_(false),
	is_cleared_to_first_seq_num_(false),
	data_buffer_(start_buffer_size),
	sequence_buffer_(start_buffer_size),
	received_frame_callback_(received_frame_callback) {
	RTC_DCHECK_LE(start_buffer_size, max_buffer_size);
	// Buffer size must always be a power of 2.
	RTC_DCHECK((start_buffer_size & (start_buffer_size - 1)) == 0);
	RTC_DCHECK((max_buffer_size & (max_buffer_size - 1)) == 0);
	}

	PacketBuffer::~PacketBuffer() {
	Clear();
	}

	bool PacketBuffer::InsertPacket(VCMPacket* packet) {
	std::vector<std::unique_ptr<RtpFrameObject>> found_frames;
	{
	rtc::CritScope lock(&crit_);

	uint16_t seq_num = packet->seqNum;
	size_t index = seq_num % size_;

	if (!first_packet_received_) {
	first_seq_num_ = seq_num;
	first_packet_received_ = true;
	} else if (AheadOf(first_seq_num_, seq_num)) {
	// If we have explicitly cleared past this packet then it's old,
	// don't insert it.
	if (is_cleared_to_first_seq_num_) {
	delete[] packet->dataPtr;
	packet->dataPtr = nullptr;
	return false;
	}

	first_seq_num_ = seq_num;
	}

	if (sequence_buffer_[index].used) {
	// Duplicate packet, just delete the payload.
	if (data_buffer_[index].seqNum == packet->seqNum) {
	delete[] packet->dataPtr;
	packet->dataPtr = nullptr;
	return true;
	}

	// The packet buffer is full, try to expand the buffer.
	while (ExpandBufferSize() && sequence_buffer_[seq_num % size_].used) {
	}
	index = seq_num % size_;

	// Packet buffer is still full.
	if (sequence_buffer_[index].used) {
	delete[] packet->dataPtr;
	packet->dataPtr = nullptr;
	return false;
	}
	}

	sequence_buffer_[index].frame_begin = packet->is_first_packet_in_frame;
	sequence_buffer_[index].frame_end = packet->markerBit;
	sequence_buffer_[index].seq_num = packet->seqNum;
	sequence_buffer_[index].continuous = false;
	sequence_buffer_[index].frame_created = false;
	sequence_buffer_[index].used = true;
	data_buffer_[index] = *packet;
	packet->dataPtr = nullptr;

	UpdateMissingPackets(packet->seqNum);

	int64_t now_ms = clock_->TimeInMilliseconds();
	last_received_packet_ms_ = rtc::Optional<int64_t>(now_ms);
	if (packet->frameType == kVideoFrameKey)
	last_received_keyframe_packet_ms_ = rtc::Optional<int64_t>(now_ms);

	found_frames = FindFrames(seq_num);
	}

	for (std::unique_ptr<RtpFrameObject>& frame : found_frames)
	received_frame_callback_->OnReceivedFrame(std::move(frame));

	return true;
	}

	void PacketBuffer::ClearTo(uint16_t seq_num) {
	rtc::CritScope lock(&crit_);

	// If the packet buffer was cleared between a frame was created and returned.
	if (!first_packet_received_)
	return;

	is_cleared_to_first_seq_num_ = true;
	while (AheadOrAt<uint16_t>(seq_num, first_seq_num_)) {
	size_t index = first_seq_num_ % size_;
	delete[] data_buffer_[index].dataPtr;
	data_buffer_[index].dataPtr = nullptr;
	sequence_buffer_[index].used = false;
	++first_seq_num_;
	}

	missing_packets_.erase(missing_packets_.begin(),
	missing_packets_.upper_bound(seq_num));
	}

	void PacketBuffer::Clear() {
	rtc::CritScope lock(&crit_);
	for (size_t i = 0; i < size_; ++i) {
	delete[] data_buffer_[i].dataPtr;
	data_buffer_[i].dataPtr = nullptr;
	sequence_buffer_[i].used = false;
	}

	first_packet_received_ = false;
	is_cleared_to_first_seq_num_ = false;
	last_received_packet_ms_.reset();
	last_received_keyframe_packet_ms_.reset();
	newest_inserted_seq_num_.reset();
	missing_packets_.clear();
	}

	void PacketBuffer::PaddingReceived(uint16_t seq_num) {
	std::vector<std::unique_ptr<RtpFrameObject>> found_frames;
	{
	rtc::CritScope lock(&crit_);
	UpdateMissingPackets(seq_num);
	found_frames = FindFrames(static_cast<uint16_t>(seq_num + 1));
	}

	for (std::unique_ptr<RtpFrameObject>& frame : found_frames)
	received_frame_callback_->OnReceivedFrame(std::move(frame));
	}

	rtc::Optional<int64_t> PacketBuffer::LastReceivedPacketMs() const {
	rtc::CritScope lock(&crit_);
	return last_received_packet_ms_;
	}

	rtc::Optional<int64_t> PacketBuffer::LastReceivedKeyframePacketMs() const {
	rtc::CritScope lock(&crit_);
	return last_received_keyframe_packet_ms_;
	}

	bool PacketBuffer::ExpandBufferSize() {
	if (size_ == max_size_) {
	LOG(LS_WARNING) << "PacketBuffer is already at max size (" << max_size_
	<< "), failed to increase size. Clearing PacketBuffer.";
	Clear();
	return false;
	}

	size_t new_size = std::min(max_size_, 2 * size_);
	std::vector<VCMPacket> new_data_buffer(new_size);
	std::vector<ContinuityInfo> new_sequence_buffer(new_size);
	for (size_t i = 0; i < size_; ++i) {
	if (sequence_buffer_[i].used) {
	size_t index = sequence_buffer_[i].seq_num % new_size;
	new_sequence_buffer[index] = sequence_buffer_[i];
	new_data_buffer[index] = data_buffer_[i];
	}
	}
	size_ = new_size;
	sequence_buffer_ = std::move(new_sequence_buffer);
	data_buffer_ = std::move(new_data_buffer);
	LOG(LS_INFO) << "PacketBuffer size expanded to " << new_size;
	return true;
	}

	bool PacketBuffer::PotentialNewFrame(uint16_t seq_num) const {
	size_t index = seq_num % size_;
	int prev_index = index > 0 ? index - 1 : size_ - 1;

	if (!sequence_buffer_[index].used)
	return false;
	if (sequence_buffer_[index].seq_num != seq_num)
	return false;
	if (sequence_buffer_[index].frame_created)
	return false;
	if (sequence_buffer_[index].frame_begin)
	return true;
	if (!sequence_buffer_[prev_index].used)
	return false;
	if (sequence_buffer_[prev_index].frame_created)
	return false;
	if (sequence_buffer_[prev_index].seq_num !=
	static_cast<uint16_t>(sequence_buffer_[index].seq_num - 1)) {
	return false;
	}
	if (sequence_buffer_[prev_index].continuous)
	return true;

	return false;
	}

	std::vector<std::unique_ptr<RtpFrameObject>> PacketBuffer::FindFrames(
	uint16_t seq_num) {
	std::vector<std::unique_ptr<RtpFrameObject>> found_frames;
	for (size_t i = 0; i < size_ && PotentialNewFrame(seq_num); ++i) {
	size_t index = seq_num % size_;
	sequence_buffer_[index].continuous = true;

	// If all packets of the frame is continuous, find the first packet of the
	// frame and create an RtpFrameObject.
	if (sequence_buffer_[index].frame_end) {
	size_t frame_size = 0;
	int max_nack_count = -1;
	uint16_t start_seq_num = seq_num;

	// Find the start index by searching backward until the packet with
	// the \|frame_begin\| flag is set.
	int start_index = index;

	bool is_h264 = data_buffer_[start_index].codec == kVideoCodecH264;
	bool is_h264_keyframe = false;
	int64_t frame_timestamp = data_buffer_[start_index].timestamp;

	// Since packet at \|data_buffer_[index]\| is already part of the frame
	// we will have at most \|size_ - 1\| packets left to check.
	for (size_t j = 0; j < size_ - 1; ++j) {
	frame_size += data_buffer_[start_index].sizeBytes;
	max_nack_count =
	std::max(max_nack_count, data_buffer_[start_index].timesNacked);
	sequence_buffer_[start_index].frame_created = true;

	if (!is_h264 && sequence_buffer_[start_index].frame_begin)
	break;

	if (is_h264 && !is_h264_keyframe) {
	const RTPVideoHeaderH264& header =
	data_buffer_[start_index].video_header.codecHeader.H264;
	for (size_t i = 0; i < header.nalus_length; ++i) {
	if (header.nalus[i].type == H264::NaluType::kIdr) {
	is_h264_keyframe = true;
	break;
	}
	}
	}

	start_index = start_index > 0 ? start_index - 1 : size_ - 1;

	// In the case of H264 we don't have a frame_begin bit (yes,
	// \|frame_begin\| might be set to true but that is a lie). So instead
	// we traverese backwards as long as we have a previous packet and
	// the timestamp of that packet is the same as this one. This may cause
	// the PacketBuffer to hand out incomplete frames.
	// See: https://bugs.chromium.org/p/webrtc/issues/detail?id=7106
	if (is_h264 &&
	(!sequence_buffer_[start_index].used \|\|
	data_buffer_[start_index].timestamp != frame_timestamp)) {
	break;
	}

	--start_seq_num;
	}

	// If this is H264 but not a keyframe, make sure there are no gaps in the
	// packet sequence numbers up until this point.
	if (is_h264 && !is_h264_keyframe &&
	missing_packets_.upper_bound(start_seq_num) !=
	missing_packets_.begin()) {
	uint16_t stop_index = (index + 1) % size_;
	while (start_index != stop_index) {
	sequence_buffer_[start_index].frame_created = false;
	start_index = (start_index + 1) % size_;
	}

	return found_frames;
	}

	missing_packets_.erase(missing_packets_.begin(),
	missing_packets_.upper_bound(seq_num));

	found_frames.emplace_back(
	new RtpFrameObject(this, start_seq_num, seq_num, frame_size,
	max_nack_count, clock_->TimeInMilliseconds()));
	}
	++seq_num;
	}
	return found_frames;
	}

	void PacketBuffer::ReturnFrame(RtpFrameObject* frame) {
	rtc::CritScope lock(&crit_);
	size_t index = frame->first_seq_num() % size_;
	size_t end = (frame->last_seq_num() + 1) % size_;
	uint16_t seq_num = frame->first_seq_num();
	while (index != end) {
	if (sequence_buffer_[index].seq_num == seq_num) {
	delete[] data_buffer_[index].dataPtr;
	data_buffer_[index].dataPtr = nullptr;
	sequence_buffer_[index].used = false;
	}

	index = (index + 1) % size_;
	++seq_num;
	}
	}

	bool PacketBuffer::GetBitstream(const RtpFrameObject& frame,
	uint8_t* destination) {
	rtc::CritScope lock(&crit_);

	size_t index = frame.first_seq_num() % size_;
	size_t end = (frame.last_seq_num() + 1) % size_;
	uint16_t seq_num = frame.first_seq_num();
	while (index != end) {
	if (!sequence_buffer_[index].used \|\|
	sequence_buffer_[index].seq_num != seq_num) {
	return false;
	}

	const uint8_t* source = data_buffer_[index].dataPtr;
	size_t length = data_buffer_[index].sizeBytes;
	memcpy(destination, source, length);
	destination += length;
	index = (index + 1) % size_;
	++seq_num;
	}
	return true;
	}

	VCMPacket* PacketBuffer::GetPacket(uint16_t seq_num) {
	size_t index = seq_num % size_;
	if (!sequence_buffer_[index].used \|\|
	seq_num != sequence_buffer_[index].seq_num) {
	return nullptr;
	}
	return &data_buffer_[index];
	}

	int PacketBuffer::AddRef() const {
	return rtc::AtomicOps::Increment(&ref_count_);
	}

	int PacketBuffer::Release() const {
	int count = rtc::AtomicOps::Decrement(&ref_count_);
	if (!count) {
	delete this;
	}
	return count;
	}

	void PacketBuffer::UpdateMissingPackets(uint16_t seq_num) {
	if (!newest_inserted_seq_num_)
	newest_inserted_seq_num_ = rtc::Optional<uint16_t>(seq_num);

	const int kMaxPaddingAge = 1000;
	if (AheadOf(seq_num, *newest_inserted_seq_num_)) {
	uint16_t old_seq_num = seq_num - kMaxPaddingAge;
	auto erase_to = missing_packets_.lower_bound(old_seq_num);
	missing_packets_.erase(missing_packets_.begin(), erase_to);

	// Guard against inserting a large amount of missing packets if there is a
	// jump in the sequence number.
	if (AheadOf(old_seq_num, *newest_inserted_seq_num_))
	*newest_inserted_seq_num_ = old_seq_num;

	++*newest_inserted_seq_num_;
	while (AheadOf(seq_num, *newest_inserted_seq_num_)) {
	missing_packets_.insert(*newest_inserted_seq_num_);
	++*newest_inserted_seq_num_;
	}
	} else {
	missing_packets_.erase(seq_num);
	}
	}

	} // namespace video_coding
	} // namespace webrtc