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 "modules/video_coding/packet_buffer.h"

 #include <string.h>

 #include <algorithm>
 #include <cstdint>
 #include <limits>
 #include <utility>
 #include <vector>

 #include "absl/types/variant.h"
 #include "api/array_view.h"
 #include "api/rtp_packet_info.h"
 #include "api/video/video_frame_type.h"
 #include "common_video/h264/h264_common.h"
 #include "modules/rtp_rtcp/source/rtp_header_extensions.h"
 #include "modules/rtp_rtcp/source/rtp_packet_received.h"
 #include "modules/rtp_rtcp/source/rtp_video_header.h"
 #include "modules/video_coding/codecs/h264/include/h264_globals.h"
 #include "rtc_base/checks.h"
 #include "rtc_base/logging.h"
 #include "rtc_base/numerics/mod_ops.h"

 namespace webrtc {
 namespace video_coding {

 PacketBuffer::Packet::Packet(const RtpPacketReceived& rtp_packet,
                              const RTPVideoHeader& video_header)
     : marker_bit(rtp_packet.Marker()),
       payload_type(rtp_packet.PayloadType()),
       seq_num(rtp_packet.SequenceNumber()),
       timestamp(rtp_packet.Timestamp()),
       times_nacked(-1),
       video_header(video_header) {}

 PacketBuffer::PacketBuffer(size_t start_buffer_size, size_t max_buffer_size)
     : max_size_(max_buffer_size),
       first_seq_num_(0),
       first_packet_received_(false),
       is_cleared_to_first_seq_num_(false),
       buffer_(start_buffer_size),
       sps_pps_idr_is_h264_keyframe_(false) {
   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();
 }

 PacketBuffer::InsertResult PacketBuffer::InsertPacket(
     std::unique_ptr<PacketBuffer::Packet> packet) {
   PacketBuffer::InsertResult result;

   uint16_t seq_num = packet->seq_num;
   size_t index = seq_num % buffer_.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, just silently ignore it.
     if (is_cleared_to_first_seq_num_) {
       return result;
     }

     first_seq_num_ = seq_num;
   }

   if (buffer_[index] != nullptr) {
     // Duplicate packet, just delete the payload.
     if (buffer_[index]->seq_num == packet->seq_num) {
       return result;
     }

     // The packet buffer is full, try to expand the buffer.
     while (ExpandBufferSize() && buffer_[seq_num % buffer_.size()] != nullptr) {
     }
     index = seq_num % buffer_.size();

     // Packet buffer is still full since we were unable to expand the buffer.
     if (buffer_[index] != nullptr) {
       // Clear the buffer, delete payload, and return false to signal that a
       // new keyframe is needed.
       RTC_LOG(LS_WARNING) << "Clear PacketBuffer and request key frame.";
       ClearInternal();
       result.buffer_cleared = true;
       return result;
     }
   }

   packet->continuous = false;
   buffer_[index] = std::move(packet);

   UpdateMissingPackets(seq_num);

   result.packets = FindFrames(seq_num);
   return result;
 }

 void PacketBuffer::ClearTo(uint16_t seq_num) {
   // We have already cleared past this sequence number, no need to do anything.
   if (is_cleared_to_first_seq_num_ &&
       AheadOf<uint16_t>(first_seq_num_, seq_num)) {
     return;
   }

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

   // Avoid iterating over the buffer more than once by capping the number of
   // iterations to the |size_| of the buffer.
   ++seq_num;
   size_t diff = ForwardDiff<uint16_t>(first_seq_num_, seq_num);
   size_t iterations = std::min(diff, buffer_.size());
   for (size_t i = 0; i < iterations; ++i) {
     auto& stored = buffer_[first_seq_num_ % buffer_.size()];
     if (stored != nullptr && AheadOf<uint16_t>(seq_num, stored->seq_num)) {
       stored = nullptr;
     }
     ++first_seq_num_;
   }

   // If |diff| is larger than |iterations| it means that we don't increment
   // |first_seq_num_| until we reach |seq_num|, so we set it here.
   first_seq_num_ = seq_num;

   is_cleared_to_first_seq_num_ = true;
   auto clear_to_it = missing_packets_.upper_bound(seq_num);
   if (clear_to_it != missing_packets_.begin()) {
     --clear_to_it;
     missing_packets_.erase(missing_packets_.begin(), clear_to_it);
   }
 }

 void PacketBuffer::Clear() {
   ClearInternal();
 }

 PacketBuffer::InsertResult PacketBuffer::InsertPadding(uint16_t seq_num) {
   PacketBuffer::InsertResult result;
   UpdateMissingPackets(seq_num);
   result.packets = FindFrames(static_cast<uint16_t>(seq_num + 1));
   return result;
 }

 void PacketBuffer::ForceSpsPpsIdrIsH264Keyframe() {
   sps_pps_idr_is_h264_keyframe_ = true;
 }

 void PacketBuffer::ClearInternal() {
   for (auto& entry : buffer_) {
     entry = nullptr;
   }

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

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

   size_t new_size = std::min(max_size_, 2 * buffer_.size());
   std::vector<std::unique_ptr<Packet>> new_buffer(new_size);
   for (std::unique_ptr<Packet>& entry : buffer_) {
     if (entry != nullptr) {
       new_buffer[entry->seq_num % new_size] = std::move(entry);
     }
   }
   buffer_ = std::move(new_buffer);
   RTC_LOG(LS_INFO) << "PacketBuffer size expanded to " << new_size;
   return true;
 }

 bool PacketBuffer::PotentialNewFrame(uint16_t seq_num) const {
   size_t index = seq_num % buffer_.size();
   int prev_index = index > 0 ? index - 1 : buffer_.size() - 1;
   const auto& entry = buffer_[index];
   const auto& prev_entry = buffer_[prev_index];

   if (entry == nullptr)
     return false;
   if (entry->seq_num != seq_num)
     return false;
   if (entry->is_first_packet_in_frame())
     return true;
   if (prev_entry == nullptr)
     return false;
   if (prev_entry->seq_num != static_cast<uint16_t>(entry->seq_num - 1))
     return false;
   if (prev_entry->timestamp != entry->timestamp)
     return false;
   if (prev_entry->continuous)
     return true;

   return false;
 }

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

     // If all packets of the frame is continuous, find the first packet of the
     // frame and add all packets of the frame to the returned packets.
     if (buffer_[index]->is_last_packet_in_frame()) {
       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;
       size_t tested_packets = 0;
       int64_t frame_timestamp = buffer_[start_index]->timestamp;

       // Identify H.264 keyframes by means of SPS, PPS, and IDR.
       bool is_h264 = buffer_[start_index]->codec() == kVideoCodecH264;
       bool has_h264_sps = false;
       bool has_h264_pps = false;
       bool has_h264_idr = false;
       bool is_h264_keyframe = false;
       int idr_width = -1;
       int idr_height = -1;
       while (true) {
         ++tested_packets;

         if (!is_h264 && buffer_[start_index]->is_first_packet_in_frame())
           break;

         if (is_h264) {
           const auto* h264_header = absl::get_if<RTPVideoHeaderH264>(
               &buffer_[start_index]->video_header.video_type_header);
           if (!h264_header || h264_header->nalus_length >= kMaxNalusPerPacket)
             return found_frames;

           for (size_t j = 0; j < h264_header->nalus_length; ++j) {
             if (h264_header->nalus[j].type == H264::NaluType::kSps) {
               has_h264_sps = true;
             } else if (h264_header->nalus[j].type == H264::NaluType::kPps) {
               has_h264_pps = true;
             } else if (h264_header->nalus[j].type == H264::NaluType::kIdr) {
               has_h264_idr = true;
             }
           }
           if ((sps_pps_idr_is_h264_keyframe_ && has_h264_idr && has_h264_sps &&
                has_h264_pps) ||
               (!sps_pps_idr_is_h264_keyframe_ && has_h264_idr)) {
             is_h264_keyframe = true;
             // Store the resolution of key frame which is the packet with
             // smallest index and valid resolution; typically its IDR or SPS
             // packet; there may be packet preceeding this packet, IDR's
             // resolution will be applied to them.
             if (buffer_[start_index]->width() > 0 &&
                 buffer_[start_index]->height() > 0) {
               idr_width = buffer_[start_index]->width();
               idr_height = buffer_[start_index]->height();
             }
           }
         }

         if (tested_packets == buffer_.size())
           break;

         start_index = start_index > 0 ? start_index - 1 : buffer_.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 && (buffer_[start_index] == nullptr ||
                         buffer_[start_index]->timestamp != frame_timestamp)) {
           break;
         }

         --start_seq_num;
       }

       if (is_h264) {
         // Warn if this is an unsafe frame.
         if (has_h264_idr && (!has_h264_sps || !has_h264_pps)) {
           RTC_LOG(LS_WARNING)
               << "Received H.264-IDR frame "
                  "(SPS: "
               << has_h264_sps << ", PPS: " << has_h264_pps << "). Treating as "
               << (sps_pps_idr_is_h264_keyframe_ ? "delta" : "key")
               << " frame since WebRTC-SpsPpsIdrIsH264Keyframe is "
               << (sps_pps_idr_is_h264_keyframe_ ? "enabled." : "disabled");
         }

         // Now that we have decided whether to treat this frame as a key frame
         // or delta frame in the frame buffer, we update the field that
         // determines if the RtpFrameObject is a key frame or delta frame.
         const size_t first_packet_index = start_seq_num % buffer_.size();
         if (is_h264_keyframe) {
           buffer_[first_packet_index]->video_header.frame_type =
               VideoFrameType::kVideoFrameKey;
           if (idr_width > 0 && idr_height > 0) {
             // IDR frame was finalized and we have the correct resolution for
             // IDR; update first packet to have same resolution as IDR.
             buffer_[first_packet_index]->video_header.width = idr_width;
             buffer_[first_packet_index]->video_header.height = idr_height;
           }
         } else {
           buffer_[first_packet_index]->video_header.frame_type =
               VideoFrameType::kVideoFrameDelta;
         }

         // If this is not a keyframe, make sure there are no gaps in the packet
         // sequence numbers up until this point.
         if (!is_h264_keyframe && missing_packets_.upper_bound(start_seq_num) !=
                                      missing_packets_.begin()) {
           return found_frames;
         }
       }

       const uint16_t end_seq_num = seq_num + 1;
       // Use uint16_t type to handle sequence number wrap around case.
       uint16_t num_packets = end_seq_num - start_seq_num;
       found_frames.reserve(found_frames.size() + num_packets);
       for (uint16_t i = start_seq_num; i != end_seq_num; ++i) {
         std::unique_ptr<Packet>& packet = buffer_[i % buffer_.size()];
         RTC_DCHECK(packet);
         RTC_DCHECK_EQ(i, packet->seq_num);
         // Ensure frame boundary flags are properly set.
         packet->video_header.is_first_packet_in_frame = (i == start_seq_num);
         packet->video_header.is_last_packet_in_frame = (i == seq_num);
         found_frames.push_back(std::move(packet));
       }

       missing_packets_.erase(missing_packets_.begin(),
                              missing_packets_.upper_bound(seq_num));
     }
     ++seq_num;
   }
   return found_frames;
 }

 void PacketBuffer::UpdateMissingPackets(uint16_t seq_num) {
   if (!newest_inserted_seq_num_)
     newest_inserted_seq_num_ = 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 "modules/video_coding/packet_buffer.h"

	#include <string.h>

	#include <algorithm>
	#include <cstdint>
	#include <limits>
	#include <utility>
	#include <vector>

	#include "absl/types/variant.h"
	#include "api/array_view.h"
	#include "api/rtp_packet_info.h"
	#include "api/video/video_frame_type.h"
	#include "common_video/h264/h264_common.h"
	#include "modules/rtp_rtcp/source/rtp_header_extensions.h"
	#include "modules/rtp_rtcp/source/rtp_packet_received.h"
	#include "modules/rtp_rtcp/source/rtp_video_header.h"
	#include "modules/video_coding/codecs/h264/include/h264_globals.h"
	#include "rtc_base/checks.h"
	#include "rtc_base/logging.h"
	#include "rtc_base/numerics/mod_ops.h"

	namespace webrtc {
	namespace video_coding {

	PacketBuffer::Packet::Packet(const RtpPacketReceived& rtp_packet,
	const RTPVideoHeader& video_header)
	: marker_bit(rtp_packet.Marker()),
	payload_type(rtp_packet.PayloadType()),
	seq_num(rtp_packet.SequenceNumber()),
	timestamp(rtp_packet.Timestamp()),
	times_nacked(-1),
	video_header(video_header) {}

	PacketBuffer::PacketBuffer(size_t start_buffer_size, size_t max_buffer_size)
	: max_size_(max_buffer_size),
	first_seq_num_(0),
	first_packet_received_(false),
	is_cleared_to_first_seq_num_(false),
	buffer_(start_buffer_size),
	sps_pps_idr_is_h264_keyframe_(false) {
	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();
	}

	PacketBuffer::InsertResult PacketBuffer::InsertPacket(
	std::unique_ptr<PacketBuffer::Packet> packet) {
	PacketBuffer::InsertResult result;

	uint16_t seq_num = packet->seq_num;
	size_t index = seq_num % buffer_.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, just silently ignore it.
	if (is_cleared_to_first_seq_num_) {
	return result;
	}

	first_seq_num_ = seq_num;
	}

	if (buffer_[index] != nullptr) {
	// Duplicate packet, just delete the payload.
	if (buffer_[index]->seq_num == packet->seq_num) {
	return result;
	}

	// The packet buffer is full, try to expand the buffer.
	while (ExpandBufferSize() && buffer_[seq_num % buffer_.size()] != nullptr) {
	}
	index = seq_num % buffer_.size();

	// Packet buffer is still full since we were unable to expand the buffer.
	if (buffer_[index] != nullptr) {
	// Clear the buffer, delete payload, and return false to signal that a
	// new keyframe is needed.
	RTC_LOG(LS_WARNING) << "Clear PacketBuffer and request key frame.";
	ClearInternal();
	result.buffer_cleared = true;
	return result;
	}
	}

	packet->continuous = false;
	buffer_[index] = std::move(packet);

	UpdateMissingPackets(seq_num);

	result.packets = FindFrames(seq_num);
	return result;
	}

	void PacketBuffer::ClearTo(uint16_t seq_num) {
	// We have already cleared past this sequence number, no need to do anything.
	if (is_cleared_to_first_seq_num_ &&
	AheadOf<uint16_t>(first_seq_num_, seq_num)) {
	return;
	}

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

	// Avoid iterating over the buffer more than once by capping the number of
	// iterations to the \|size_\| of the buffer.
	++seq_num;
	size_t diff = ForwardDiff<uint16_t>(first_seq_num_, seq_num);
	size_t iterations = std::min(diff, buffer_.size());
	for (size_t i = 0; i < iterations; ++i) {
	auto& stored = buffer_[first_seq_num_ % buffer_.size()];
	if (stored != nullptr && AheadOf<uint16_t>(seq_num, stored->seq_num)) {
	stored = nullptr;
	}
	++first_seq_num_;
	}

	// If \|diff\| is larger than \|iterations\| it means that we don't increment
	// \|first_seq_num_\| until we reach \|seq_num\|, so we set it here.
	first_seq_num_ = seq_num;

	is_cleared_to_first_seq_num_ = true;
	auto clear_to_it = missing_packets_.upper_bound(seq_num);
	if (clear_to_it != missing_packets_.begin()) {
	--clear_to_it;
	missing_packets_.erase(missing_packets_.begin(), clear_to_it);
	}
	}

	void PacketBuffer::Clear() {
	ClearInternal();
	}

	PacketBuffer::InsertResult PacketBuffer::InsertPadding(uint16_t seq_num) {
	PacketBuffer::InsertResult result;
	UpdateMissingPackets(seq_num);
	result.packets = FindFrames(static_cast<uint16_t>(seq_num + 1));
	return result;
	}

	void PacketBuffer::ForceSpsPpsIdrIsH264Keyframe() {
	sps_pps_idr_is_h264_keyframe_ = true;
	}

	void PacketBuffer::ClearInternal() {
	for (auto& entry : buffer_) {
	entry = nullptr;
	}

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

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

	size_t new_size = std::min(max_size_, 2 * buffer_.size());
	std::vector<std::unique_ptr<Packet>> new_buffer(new_size);
	for (std::unique_ptr<Packet>& entry : buffer_) {
	if (entry != nullptr) {
	new_buffer[entry->seq_num % new_size] = std::move(entry);
	}
	}
	buffer_ = std::move(new_buffer);
	RTC_LOG(LS_INFO) << "PacketBuffer size expanded to " << new_size;
	return true;
	}

	bool PacketBuffer::PotentialNewFrame(uint16_t seq_num) const {
	size_t index = seq_num % buffer_.size();
	int prev_index = index > 0 ? index - 1 : buffer_.size() - 1;
	const auto& entry = buffer_[index];
	const auto& prev_entry = buffer_[prev_index];

	if (entry == nullptr)
	return false;
	if (entry->seq_num != seq_num)
	return false;
	if (entry->is_first_packet_in_frame())
	return true;
	if (prev_entry == nullptr)
	return false;
	if (prev_entry->seq_num != static_cast<uint16_t>(entry->seq_num - 1))
	return false;
	if (prev_entry->timestamp != entry->timestamp)
	return false;
	if (prev_entry->continuous)
	return true;

	return false;
	}

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

	// If all packets of the frame is continuous, find the first packet of the
	// frame and add all packets of the frame to the returned packets.
	if (buffer_[index]->is_last_packet_in_frame()) {
	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;
	size_t tested_packets = 0;
	int64_t frame_timestamp = buffer_[start_index]->timestamp;

	// Identify H.264 keyframes by means of SPS, PPS, and IDR.
	bool is_h264 = buffer_[start_index]->codec() == kVideoCodecH264;
	bool has_h264_sps = false;
	bool has_h264_pps = false;
	bool has_h264_idr = false;
	bool is_h264_keyframe = false;
	int idr_width = -1;
	int idr_height = -1;
	while (true) {
	++tested_packets;

	if (!is_h264 && buffer_[start_index]->is_first_packet_in_frame())
	break;

	if (is_h264) {
	const auto* h264_header = absl::get_if<RTPVideoHeaderH264>(
	&buffer_[start_index]->video_header.video_type_header);
	if (!h264_header \|\| h264_header->nalus_length >= kMaxNalusPerPacket)
	return found_frames;

	for (size_t j = 0; j < h264_header->nalus_length; ++j) {
	if (h264_header->nalus[j].type == H264::NaluType::kSps) {
	has_h264_sps = true;
	} else if (h264_header->nalus[j].type == H264::NaluType::kPps) {
	has_h264_pps = true;
	} else if (h264_header->nalus[j].type == H264::NaluType::kIdr) {
	has_h264_idr = true;
	}
	}
	if ((sps_pps_idr_is_h264_keyframe_ && has_h264_idr && has_h264_sps &&
	has_h264_pps) \|\|
	(!sps_pps_idr_is_h264_keyframe_ && has_h264_idr)) {
	is_h264_keyframe = true;
	// Store the resolution of key frame which is the packet with
	// smallest index and valid resolution; typically its IDR or SPS
	// packet; there may be packet preceeding this packet, IDR's
	// resolution will be applied to them.
	if (buffer_[start_index]->width() > 0 &&
	buffer_[start_index]->height() > 0) {
	idr_width = buffer_[start_index]->width();
	idr_height = buffer_[start_index]->height();
	}
	}
	}

	if (tested_packets == buffer_.size())
	break;

	start_index = start_index > 0 ? start_index - 1 : buffer_.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 && (buffer_[start_index] == nullptr \|\|
	buffer_[start_index]->timestamp != frame_timestamp)) {
	break;
	}

	--start_seq_num;
	}

	if (is_h264) {
	// Warn if this is an unsafe frame.
	if (has_h264_idr && (!has_h264_sps \|\| !has_h264_pps)) {
	RTC_LOG(LS_WARNING)
	<< "Received H.264-IDR frame "
	"(SPS: "
	<< has_h264_sps << ", PPS: " << has_h264_pps << "). Treating as "
	<< (sps_pps_idr_is_h264_keyframe_ ? "delta" : "key")
	<< " frame since WebRTC-SpsPpsIdrIsH264Keyframe is "
	<< (sps_pps_idr_is_h264_keyframe_ ? "enabled." : "disabled");
	}

	// Now that we have decided whether to treat this frame as a key frame
	// or delta frame in the frame buffer, we update the field that
	// determines if the RtpFrameObject is a key frame or delta frame.
	const size_t first_packet_index = start_seq_num % buffer_.size();
	if (is_h264_keyframe) {
	buffer_[first_packet_index]->video_header.frame_type =
	VideoFrameType::kVideoFrameKey;
	if (idr_width > 0 && idr_height > 0) {
	// IDR frame was finalized and we have the correct resolution for
	// IDR; update first packet to have same resolution as IDR.
	buffer_[first_packet_index]->video_header.width = idr_width;
	buffer_[first_packet_index]->video_header.height = idr_height;
	}
	} else {
	buffer_[first_packet_index]->video_header.frame_type =
	VideoFrameType::kVideoFrameDelta;
	}

	// If this is not a keyframe, make sure there are no gaps in the packet
	// sequence numbers up until this point.
	if (!is_h264_keyframe && missing_packets_.upper_bound(start_seq_num) !=
	missing_packets_.begin()) {
	return found_frames;
	}
	}

	const uint16_t end_seq_num = seq_num + 1;
	// Use uint16_t type to handle sequence number wrap around case.
	uint16_t num_packets = end_seq_num - start_seq_num;
	found_frames.reserve(found_frames.size() + num_packets);
	for (uint16_t i = start_seq_num; i != end_seq_num; ++i) {
	std::unique_ptr<Packet>& packet = buffer_[i % buffer_.size()];
	RTC_DCHECK(packet);
	RTC_DCHECK_EQ(i, packet->seq_num);
	// Ensure frame boundary flags are properly set.
	packet->video_header.is_first_packet_in_frame = (i == start_seq_num);
	packet->video_header.is_last_packet_in_frame = (i == seq_num);
	found_frames.push_back(std::move(packet));
	}

	missing_packets_.erase(missing_packets_.begin(),
	missing_packets_.upper_bound(seq_num));
	}
	++seq_num;
	}
	return found_frames;
	}

	void PacketBuffer::UpdateMissingPackets(uint16_t seq_num) {
	if (!newest_inserted_seq_num_)
	newest_inserted_seq_num_ = 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