modules/rtp_rtcp/source/rtp_format_h264.cc - src/webrtc - Git at Google

 /*
  *  Copyright (c) 2014 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/rtp_rtcp/source/rtp_format_h264.h"

 #include <string.h>
 #include <vector>

 #include "webrtc/base/checks.h"
 #include "webrtc/base/logging.h"
 #include "webrtc/modules/include/module_common_types.h"
 #include "webrtc/modules/rtp_rtcp/source/byte_io.h"
 #include "webrtc/common_video/h264/sps_vui_rewriter.h"
 #include "webrtc/common_video/h264/h264_common.h"
 #include "webrtc/common_video/h264/sps_parser.h"
 #include "webrtc/system_wrappers/include/metrics.h"

 namespace webrtc {
 namespace {

 static const size_t kNalHeaderSize = 1;
 static const size_t kFuAHeaderSize = 2;
 static const size_t kLengthFieldSize = 2;
 static const size_t kStapAHeaderSize = kNalHeaderSize + kLengthFieldSize;

 static const char* kSpsValidHistogramName = "WebRTC.Video.H264.SpsValid";
 enum SpsValidEvent {
   kReceivedSpsPocOk = 0,
   kReceivedSpsVuiOk = 1,
   kReceivedSpsRewritten = 2,
   kReceivedSpsParseFailure = 3,
   kSentSpsPocOk = 4,
   kSentSpsVuiOk = 5,
   kSentSpsRewritten = 6,
   kSentSpsParseFailure = 7,
   kSpsRewrittenMax = 8
 };

 // Bit masks for FU (A and B) indicators.
 enum NalDefs : uint8_t { kFBit = 0x80, kNriMask = 0x60, kTypeMask = 0x1F };

 // Bit masks for FU (A and B) headers.
 enum FuDefs : uint8_t { kSBit = 0x80, kEBit = 0x40, kRBit = 0x20 };

 // TODO(pbos): Avoid parsing this here as well as inside the jitter buffer.
 bool ParseStapAStartOffsets(const uint8_t* nalu_ptr,
                             size_t length_remaining,
                             std::vector<size_t>* offsets) {
   size_t offset = 0;
   while (length_remaining > 0) {
     // Buffer doesn't contain room for additional nalu length.
     if (length_remaining < sizeof(uint16_t))
       return false;
     uint16_t nalu_size = ByteReader<uint16_t>::ReadBigEndian(nalu_ptr);
     nalu_ptr += sizeof(uint16_t);
     length_remaining -= sizeof(uint16_t);
     if (nalu_size > length_remaining)
       return false;
     nalu_ptr += nalu_size;
     length_remaining -= nalu_size;

     offsets->push_back(offset + kStapAHeaderSize);
     offset += kLengthFieldSize + nalu_size;
   }
   return true;
 }

 }  // namespace

 RtpPacketizerH264::RtpPacketizerH264(FrameType frame_type,
                                      size_t max_payload_len)
     : max_payload_len_(max_payload_len) {}

 RtpPacketizerH264::~RtpPacketizerH264() {
 }

 RtpPacketizerH264::Fragment::Fragment(const uint8_t* buffer, size_t length)
     : buffer(buffer), length(length) {}
 RtpPacketizerH264::Fragment::Fragment(const Fragment& fragment)
     : buffer(fragment.buffer), length(fragment.length) {}

 void RtpPacketizerH264::SetPayloadData(
     const uint8_t* payload_data,
     size_t payload_size,
     const RTPFragmentationHeader* fragmentation) {
   RTC_DCHECK(packets_.empty());
   RTC_DCHECK(input_fragments_.empty());
   RTC_DCHECK(fragmentation);
   for (int i = 0; i < fragmentation->fragmentationVectorSize; ++i) {
     const uint8_t* buffer =
         &payload_data[fragmentation->fragmentationOffset[i]];
     size_t length = fragmentation->fragmentationLength[i];

     bool updated_sps = false;
     H264::NaluType nalu_type = H264::ParseNaluType(buffer[0]);
     if (nalu_type == H264::NaluType::kSps) {
       // Check if stream uses picture order count type 0, and if so rewrite it
       // to enable faster decoding. Streams in that format incur additional
       // delay because it allows decode order to differ from render order.
       // The mechanism used is to rewrite (edit or add) the SPS's VUI to contain
       // restrictions on the maximum number of reordered pictures. This reduces
       // latency significantly, though it still adds about a frame of latency to
       // decoding.
       // Note that we do this rewriting both here (send side, in order to
       // protect legacy receive clients) and below in
       // RtpDepacketizerH264::ParseSingleNalu (receive side, in orderer to
       // protect us from unknown or legacy send clients).

       // Create temporary RBSP decoded buffer of the payload (exlcuding the
       // leading nalu type header byte (the SpsParser uses only the payload).
       std::unique_ptr<rtc::Buffer> rbsp_buffer = H264::ParseRbsp(
           buffer + H264::kNaluTypeSize, length - H264::kNaluTypeSize);
       rtc::Optional<SpsParser::SpsState> sps;

       std::unique_ptr<rtc::Buffer> output_buffer(new rtc::Buffer());
       // Add the type header to the output buffer first, so that the rewriter
       // can append modified payload on top of that.
       output_buffer->AppendData(buffer[0]);
       SpsVuiRewriter::ParseResult result = SpsVuiRewriter::ParseAndRewriteSps(
           rbsp_buffer->data(), rbsp_buffer->size(), &sps, output_buffer.get());

       switch (result) {
         case SpsVuiRewriter::ParseResult::kVuiRewritten:
           input_fragments_.push_back(
               Fragment(output_buffer->data(), output_buffer->size()));
           input_fragments_.rbegin()->tmp_buffer = std::move(output_buffer);
           updated_sps = true;
           RTC_HISTOGRAM_ENUMERATION(kSpsValidHistogramName,
                                     SpsValidEvent::kSentSpsRewritten,
                                     SpsValidEvent::kSpsRewrittenMax);
           break;
         case SpsVuiRewriter::ParseResult::kPocOk:
           RTC_HISTOGRAM_ENUMERATION(kSpsValidHistogramName,
                                     SpsValidEvent::kSentSpsPocOk,
                                     SpsValidEvent::kSpsRewrittenMax);
           break;
         case SpsVuiRewriter::ParseResult::kVuiOk:
           RTC_HISTOGRAM_ENUMERATION(kSpsValidHistogramName,
                                     SpsValidEvent::kSentSpsVuiOk,
                                     SpsValidEvent::kSpsRewrittenMax);
           break;
         case SpsVuiRewriter::ParseResult::kFailure:
           RTC_HISTOGRAM_ENUMERATION(kSpsValidHistogramName,
                                     SpsValidEvent::kSentSpsParseFailure,
                                     SpsValidEvent::kSpsRewrittenMax);
           break;
       }
     }

     if (!updated_sps)
       input_fragments_.push_back(Fragment(buffer, length));
   }
   GeneratePackets();
 }

 void RtpPacketizerH264::GeneratePackets() {
   for (size_t i = 0; i < input_fragments_.size();) {
     if (input_fragments_[i].length > max_payload_len_) {
       PacketizeFuA(i);
       ++i;
     } else {
       i = PacketizeStapA(i);
     }
   }
 }

 void RtpPacketizerH264::PacketizeFuA(size_t fragment_index) {
   // Fragment payload into packets (FU-A).
   // Strip out the original header and leave room for the FU-A header.
   const Fragment& fragment = input_fragments_[fragment_index];

   size_t fragment_length = fragment.length - kNalHeaderSize;
   size_t offset = kNalHeaderSize;
   size_t bytes_available = max_payload_len_ - kFuAHeaderSize;
   const size_t num_fragments =
       (fragment_length + (bytes_available - 1)) / bytes_available;

   const size_t avg_size = (fragment_length + num_fragments - 1) / num_fragments;
   while (fragment_length > 0) {
     size_t packet_length = avg_size;
     if (fragment_length < avg_size)
       packet_length = fragment_length;
     packets_.push(PacketUnit(Fragment(fragment.buffer + offset, packet_length),
                              offset - kNalHeaderSize == 0,
                              fragment_length == packet_length, false,
                              fragment.buffer[0]));
     offset += packet_length;
     fragment_length -= packet_length;
   }
   RTC_CHECK_EQ(0u, fragment_length);
 }

 size_t RtpPacketizerH264::PacketizeStapA(size_t fragment_index) {
   // Aggregate fragments into one packet (STAP-A).
   size_t payload_size_left = max_payload_len_;
   int aggregated_fragments = 0;
   size_t fragment_headers_length = 0;
   const Fragment* fragment = &input_fragments_[fragment_index];
   RTC_CHECK_GE(payload_size_left, fragment->length);
   while (payload_size_left >= fragment->length + fragment_headers_length) {
     RTC_CHECK_GT(fragment->length, 0u);
     packets_.push(PacketUnit(*fragment, aggregated_fragments == 0, false, true,
                              fragment->buffer[0]));
     payload_size_left -= fragment->length;
     payload_size_left -= fragment_headers_length;

     // Next fragment.
     ++fragment_index;
     if (fragment_index == input_fragments_.size())
       break;
     fragment = &input_fragments_[fragment_index];

     fragment_headers_length = kLengthFieldSize;
     // If we are going to try to aggregate more fragments into this packet
     // we need to add the STAP-A NALU header and a length field for the first
     // NALU of this packet.
     if (aggregated_fragments == 0)
       fragment_headers_length += kNalHeaderSize + kLengthFieldSize;
     ++aggregated_fragments;
   }
   packets_.back().last_fragment = true;
   return fragment_index;
 }

 bool RtpPacketizerH264::NextPacket(uint8_t* buffer,
                                    size_t* bytes_to_send,
                                    bool* last_packet) {
   *bytes_to_send = 0;
   if (packets_.empty()) {
     *bytes_to_send = 0;
     *last_packet = true;
     return false;
   }

   PacketUnit packet = packets_.front();

   if (packet.first_fragment && packet.last_fragment) {
     // Single NAL unit packet.
     *bytes_to_send = packet.source_fragment.length;
     memcpy(buffer, packet.source_fragment.buffer, *bytes_to_send);
     packets_.pop();
     input_fragments_.pop_front();
     RTC_CHECK_LE(*bytes_to_send, max_payload_len_);
   } else if (packet.aggregated) {
     NextAggregatePacket(buffer, bytes_to_send);
     RTC_CHECK_LE(*bytes_to_send, max_payload_len_);
   } else {
     NextFragmentPacket(buffer, bytes_to_send);
     RTC_CHECK_LE(*bytes_to_send, max_payload_len_);
   }
   *last_packet = packets_.empty();
   return true;
 }

 void RtpPacketizerH264::NextAggregatePacket(uint8_t* buffer,
                                             size_t* bytes_to_send) {
   PacketUnit* packet = &packets_.front();
   RTC_CHECK(packet->first_fragment);
   // STAP-A NALU header.
   buffer[0] = (packet->header & (kFBit | kNriMask)) | H264::NaluType::kStapA;
   int index = kNalHeaderSize;
   *bytes_to_send += kNalHeaderSize;
   while (packet->aggregated) {
     const Fragment& fragment = packet->source_fragment;
     // Add NAL unit length field.
     ByteWriter<uint16_t>::WriteBigEndian(&buffer[index], fragment.length);
     index += kLengthFieldSize;
     *bytes_to_send += kLengthFieldSize;
     // Add NAL unit.
     memcpy(&buffer[index], fragment.buffer, fragment.length);
     index += fragment.length;
     *bytes_to_send += fragment.length;
     packets_.pop();
     input_fragments_.pop_front();
     if (packet->last_fragment)
       break;
     packet = &packets_.front();
   }
   RTC_CHECK(packet->last_fragment);
 }

 void RtpPacketizerH264::NextFragmentPacket(uint8_t* buffer,
                                            size_t* bytes_to_send) {
   PacketUnit* packet = &packets_.front();
   // NAL unit fragmented over multiple packets (FU-A).
   // We do not send original NALU header, so it will be replaced by the
   // FU indicator header of the first packet.
   uint8_t fu_indicator =
       (packet->header & (kFBit | kNriMask)) | H264::NaluType::kFuA;
   uint8_t fu_header = 0;

   // S | E | R | 5 bit type.
   fu_header |= (packet->first_fragment ? kSBit : 0);
   fu_header |= (packet->last_fragment ? kEBit : 0);
   uint8_t type = packet->header & kTypeMask;
   fu_header |= type;
   buffer[0] = fu_indicator;
   buffer[1] = fu_header;

   const Fragment& fragment = packet->source_fragment;
   *bytes_to_send = fragment.length + kFuAHeaderSize;
   memcpy(buffer + kFuAHeaderSize, fragment.buffer, fragment.length);
   if (packet->last_fragment)
     input_fragments_.pop_front();
   packets_.pop();
 }

 ProtectionType RtpPacketizerH264::GetProtectionType() {
   return kProtectedPacket;
 }

 StorageType RtpPacketizerH264::GetStorageType(
     uint32_t retransmission_settings) {
   return kAllowRetransmission;
 }

 std::string RtpPacketizerH264::ToString() {
   return "RtpPacketizerH264";
 }

 RtpDepacketizerH264::RtpDepacketizerH264() : offset_(0), length_(0) {}
 RtpDepacketizerH264::~RtpDepacketizerH264() {}

 bool RtpDepacketizerH264::Parse(ParsedPayload* parsed_payload,
                                 const uint8_t* payload_data,
                                 size_t payload_data_length) {
   RTC_CHECK(parsed_payload != nullptr);
   if (payload_data_length == 0) {
     LOG(LS_ERROR) << "Empty payload.";
     return false;
   }

   offset_ = 0;
   length_ = payload_data_length;
   modified_buffer_.reset();

   uint8_t nal_type = payload_data[0] & kTypeMask;
   if (nal_type == H264::NaluType::kFuA) {
     // Fragmented NAL units (FU-A).
     if (!ParseFuaNalu(parsed_payload, payload_data))
       return false;
   } else {
     // We handle STAP-A and single NALU's the same way here. The jitter buffer
     // will depacketize the STAP-A into NAL units later.
     // TODO(sprang): Parse STAP-A offsets here and store in fragmentation vec.
     if (!ProcessStapAOrSingleNalu(parsed_payload, payload_data))
       return false;
   }

   const uint8_t* payload =
       modified_buffer_ ? modified_buffer_->data() : payload_data;

   parsed_payload->payload = payload + offset_;
   parsed_payload->payload_length = length_;
   return true;
 }

 bool RtpDepacketizerH264::ProcessStapAOrSingleNalu(
     ParsedPayload* parsed_payload,
     const uint8_t* payload_data) {
   parsed_payload->type.Video.width = 0;
   parsed_payload->type.Video.height = 0;
   parsed_payload->type.Video.codec = kRtpVideoH264;
   parsed_payload->type.Video.isFirstPacket = true;
   RTPVideoHeaderH264* h264_header =
       &parsed_payload->type.Video.codecHeader.H264;

   const uint8_t* nalu_start = payload_data + kNalHeaderSize;
   const size_t nalu_length = length_ - kNalHeaderSize;
   uint8_t nal_type = payload_data[0] & kTypeMask;
   std::vector<size_t> nalu_start_offsets;
   if (nal_type == H264::NaluType::kStapA) {
     // Skip the StapA header (StapA NAL type + length).
     if (length_ <= kStapAHeaderSize) {
       LOG(LS_ERROR) << "StapA header truncated.";
       return false;
     }

     if (!ParseStapAStartOffsets(nalu_start, nalu_length, &nalu_start_offsets)) {
       LOG(LS_ERROR) << "StapA packet with incorrect NALU packet lengths.";
       return false;
     }

     h264_header->packetization_type = kH264StapA;
     nal_type = payload_data[kStapAHeaderSize] & kTypeMask;
   } else {
     h264_header->packetization_type = kH264SingleNalu;
     nalu_start_offsets.push_back(0);
   }
   h264_header->nalu_type = nal_type;
   parsed_payload->frame_type = kVideoFrameDelta;

   nalu_start_offsets.push_back(length_ + kLengthFieldSize);  // End offset.
   for (size_t i = 0; i < nalu_start_offsets.size() - 1; ++i) {
     size_t start_offset = nalu_start_offsets[i];
     // End offset is actually start offset for next unit, excluding length field
     // so remove that from this units length.
     size_t end_offset = nalu_start_offsets[i + 1] - kLengthFieldSize;
     if (end_offset - start_offset < H264::kNaluTypeSize) {
       LOG(LS_ERROR) << "STAP-A packet too short";
       return false;
     }

     nal_type = payload_data[start_offset] & kTypeMask;
     start_offset += H264::kNaluTypeSize;

     if (nal_type == H264::NaluType::kSps) {
       // Check if VUI is present in SPS and if it needs to be modified to avoid
       // excessive decoder latency.

       // Copy any previous data first (likely just the first header).
       std::unique_ptr<rtc::Buffer> output_buffer(new rtc::Buffer());
       if (start_offset)
         output_buffer->AppendData(payload_data, start_offset);

       // RBSP decode of payload data.
       std::unique_ptr<rtc::Buffer> rbsp_buffer = H264::ParseRbsp(
           &payload_data[start_offset], end_offset - start_offset);
       rtc::Optional<SpsParser::SpsState> sps;

       SpsVuiRewriter::ParseResult result = SpsVuiRewriter::ParseAndRewriteSps(
           rbsp_buffer->data(), rbsp_buffer->size(), &sps, output_buffer.get());
       switch (result) {
         case SpsVuiRewriter::ParseResult::kVuiRewritten:
           if (modified_buffer_) {
             LOG(LS_WARNING) << "More than one H264 SPS NAL units needing "
                                "rewriting found within a single STAP-A packet. "
                                "Keeping the first and rewriting the last.";
           }

           // Rewrite length field to new SPS size.
           if (h264_header->packetization_type == kH264StapA) {
             size_t length_field_offset =
                 start_offset - (H264::kNaluTypeSize + kLengthFieldSize);
             // Stap-A Length includes payload data and type header.
             size_t rewritten_size =
                 output_buffer->size() - start_offset + H264::kNaluTypeSize;
             ByteWriter<uint16_t>::WriteBigEndian(
                 &(*output_buffer)[length_field_offset], rewritten_size);
           }

           // Append rest of packet.
           output_buffer->AppendData(&payload_data[end_offset],
                                     nalu_length + kNalHeaderSize - end_offset);

           modified_buffer_ = std::move(output_buffer);
           length_ = modified_buffer_->size();

           RTC_HISTOGRAM_ENUMERATION(kSpsValidHistogramName,
                                     SpsValidEvent::kReceivedSpsRewritten,
                                     SpsValidEvent::kSpsRewrittenMax);
           break;
         case SpsVuiRewriter::ParseResult::kPocOk:
           RTC_HISTOGRAM_ENUMERATION(kSpsValidHistogramName,
                                     SpsValidEvent::kReceivedSpsPocOk,
                                     SpsValidEvent::kSpsRewrittenMax);
           break;
         case SpsVuiRewriter::ParseResult::kVuiOk:
           RTC_HISTOGRAM_ENUMERATION(kSpsValidHistogramName,
                                     SpsValidEvent::kReceivedSpsVuiOk,
                                     SpsValidEvent::kSpsRewrittenMax);
           break;
         case SpsVuiRewriter::ParseResult::kFailure:
           RTC_HISTOGRAM_ENUMERATION(kSpsValidHistogramName,
                                     SpsValidEvent::kReceivedSpsParseFailure,
                                     SpsValidEvent::kSpsRewrittenMax);
           break;
       }

       if (sps) {
         parsed_payload->type.Video.width = sps->width;
         parsed_payload->type.Video.height = sps->height;
       }
       parsed_payload->frame_type = kVideoFrameKey;
     } else if (nal_type == H264::NaluType::kPps ||
                nal_type == H264::NaluType::kSei ||
                nal_type == H264::NaluType::kIdr) {
       parsed_payload->frame_type = kVideoFrameKey;
     }
   }

   return true;
 }

 bool RtpDepacketizerH264::ParseFuaNalu(
     RtpDepacketizer::ParsedPayload* parsed_payload,
     const uint8_t* payload_data) {
   if (length_ < kFuAHeaderSize) {
     LOG(LS_ERROR) << "FU-A NAL units truncated.";
     return false;
   }
   uint8_t fnri = payload_data[0] & (kFBit | kNriMask);
   uint8_t original_nal_type = payload_data[1] & kTypeMask;
   bool first_fragment = (payload_data[1] & kSBit) > 0;

   if (first_fragment) {
     offset_ = 0;
     length_ -= kNalHeaderSize;
     uint8_t original_nal_header = fnri | original_nal_type;
     modified_buffer_.reset(new rtc::Buffer());
     modified_buffer_->AppendData(payload_data + kNalHeaderSize, length_);
     (*modified_buffer_)[0] = original_nal_header;
   } else {
     offset_ = kFuAHeaderSize;
     length_ -= kFuAHeaderSize;
   }

   if (original_nal_type == H264::NaluType::kIdr) {
     parsed_payload->frame_type = kVideoFrameKey;
   } else {
     parsed_payload->frame_type = kVideoFrameDelta;
   }
   parsed_payload->type.Video.width = 0;
   parsed_payload->type.Video.height = 0;
   parsed_payload->type.Video.codec = kRtpVideoH264;
   parsed_payload->type.Video.isFirstPacket = first_fragment;
   RTPVideoHeaderH264* h264_header =
       &parsed_payload->type.Video.codecHeader.H264;
   h264_header->packetization_type = kH264FuA;
   h264_header->nalu_type = original_nal_type;
   return true;
 }

 }  // namespace webrtc
	/*
	* Copyright (c) 2014 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/rtp_rtcp/source/rtp_format_h264.h"

	#include <string.h>
	#include <vector>

	#include "webrtc/base/checks.h"
	#include "webrtc/base/logging.h"
	#include "webrtc/modules/include/module_common_types.h"
	#include "webrtc/modules/rtp_rtcp/source/byte_io.h"
	#include "webrtc/common_video/h264/sps_vui_rewriter.h"
	#include "webrtc/common_video/h264/h264_common.h"
	#include "webrtc/common_video/h264/sps_parser.h"
	#include "webrtc/system_wrappers/include/metrics.h"

	namespace webrtc {
	namespace {

	static const size_t kNalHeaderSize = 1;
	static const size_t kFuAHeaderSize = 2;
	static const size_t kLengthFieldSize = 2;
	static const size_t kStapAHeaderSize = kNalHeaderSize + kLengthFieldSize;

	static const char* kSpsValidHistogramName = "WebRTC.Video.H264.SpsValid";
	enum SpsValidEvent {
	kReceivedSpsPocOk = 0,
	kReceivedSpsVuiOk = 1,
	kReceivedSpsRewritten = 2,
	kReceivedSpsParseFailure = 3,
	kSentSpsPocOk = 4,
	kSentSpsVuiOk = 5,
	kSentSpsRewritten = 6,
	kSentSpsParseFailure = 7,
	kSpsRewrittenMax = 8
	};

	// Bit masks for FU (A and B) indicators.
	enum NalDefs : uint8_t { kFBit = 0x80, kNriMask = 0x60, kTypeMask = 0x1F };

	// Bit masks for FU (A and B) headers.
	enum FuDefs : uint8_t { kSBit = 0x80, kEBit = 0x40, kRBit = 0x20 };

	// TODO(pbos): Avoid parsing this here as well as inside the jitter buffer.
	bool ParseStapAStartOffsets(const uint8_t* nalu_ptr,
	size_t length_remaining,
	std::vector<size_t>* offsets) {
	size_t offset = 0;
	while (length_remaining > 0) {
	// Buffer doesn't contain room for additional nalu length.
	if (length_remaining < sizeof(uint16_t))
	return false;
	uint16_t nalu_size = ByteReader<uint16_t>::ReadBigEndian(nalu_ptr);
	nalu_ptr += sizeof(uint16_t);
	length_remaining -= sizeof(uint16_t);
	if (nalu_size > length_remaining)
	return false;
	nalu_ptr += nalu_size;
	length_remaining -= nalu_size;

	offsets->push_back(offset + kStapAHeaderSize);
	offset += kLengthFieldSize + nalu_size;
	}
	return true;
	}

	} // namespace

	RtpPacketizerH264::RtpPacketizerH264(FrameType frame_type,
	size_t max_payload_len)
	: max_payload_len_(max_payload_len) {}

	RtpPacketizerH264::~RtpPacketizerH264() {
	}

	RtpPacketizerH264::Fragment::Fragment(const uint8_t* buffer, size_t length)
	: buffer(buffer), length(length) {}
	RtpPacketizerH264::Fragment::Fragment(const Fragment& fragment)
	: buffer(fragment.buffer), length(fragment.length) {}

	void RtpPacketizerH264::SetPayloadData(
	const uint8_t* payload_data,
	size_t payload_size,
	const RTPFragmentationHeader* fragmentation) {
	RTC_DCHECK(packets_.empty());
	RTC_DCHECK(input_fragments_.empty());
	RTC_DCHECK(fragmentation);
	for (int i = 0; i < fragmentation->fragmentationVectorSize; ++i) {
	const uint8_t* buffer =
	&payload_data[fragmentation->fragmentationOffset[i]];
	size_t length = fragmentation->fragmentationLength[i];

	bool updated_sps = false;
	H264::NaluType nalu_type = H264::ParseNaluType(buffer[0]);
	if (nalu_type == H264::NaluType::kSps) {
	// Check if stream uses picture order count type 0, and if so rewrite it
	// to enable faster decoding. Streams in that format incur additional
	// delay because it allows decode order to differ from render order.
	// The mechanism used is to rewrite (edit or add) the SPS's VUI to contain
	// restrictions on the maximum number of reordered pictures. This reduces
	// latency significantly, though it still adds about a frame of latency to
	// decoding.
	// Note that we do this rewriting both here (send side, in order to
	// protect legacy receive clients) and below in
	// RtpDepacketizerH264::ParseSingleNalu (receive side, in orderer to
	// protect us from unknown or legacy send clients).

	// Create temporary RBSP decoded buffer of the payload (exlcuding the
	// leading nalu type header byte (the SpsParser uses only the payload).
	std::unique_ptr<rtc::Buffer> rbsp_buffer = H264::ParseRbsp(
	buffer + H264::kNaluTypeSize, length - H264::kNaluTypeSize);
	rtc::Optional<SpsParser::SpsState> sps;

	std::unique_ptr<rtc::Buffer> output_buffer(new rtc::Buffer());
	// Add the type header to the output buffer first, so that the rewriter
	// can append modified payload on top of that.
	output_buffer->AppendData(buffer[0]);
	SpsVuiRewriter::ParseResult result = SpsVuiRewriter::ParseAndRewriteSps(
	rbsp_buffer->data(), rbsp_buffer->size(), &sps, output_buffer.get());

	switch (result) {
	case SpsVuiRewriter::ParseResult::kVuiRewritten:
	input_fragments_.push_back(
	Fragment(output_buffer->data(), output_buffer->size()));
	input_fragments_.rbegin()->tmp_buffer = std::move(output_buffer);
	updated_sps = true;
	RTC_HISTOGRAM_ENUMERATION(kSpsValidHistogramName,
	SpsValidEvent::kSentSpsRewritten,
	SpsValidEvent::kSpsRewrittenMax);
	break;
	case SpsVuiRewriter::ParseResult::kPocOk:
	RTC_HISTOGRAM_ENUMERATION(kSpsValidHistogramName,
	SpsValidEvent::kSentSpsPocOk,
	SpsValidEvent::kSpsRewrittenMax);
	break;
	case SpsVuiRewriter::ParseResult::kVuiOk:
	RTC_HISTOGRAM_ENUMERATION(kSpsValidHistogramName,
	SpsValidEvent::kSentSpsVuiOk,
	SpsValidEvent::kSpsRewrittenMax);
	break;
	case SpsVuiRewriter::ParseResult::kFailure:
	RTC_HISTOGRAM_ENUMERATION(kSpsValidHistogramName,
	SpsValidEvent::kSentSpsParseFailure,
	SpsValidEvent::kSpsRewrittenMax);
	break;
	}
	}

	if (!updated_sps)
	input_fragments_.push_back(Fragment(buffer, length));
	}
	GeneratePackets();
	}

	void RtpPacketizerH264::GeneratePackets() {
	for (size_t i = 0; i < input_fragments_.size();) {
	if (input_fragments_[i].length > max_payload_len_) {
	PacketizeFuA(i);
	++i;
	} else {
	i = PacketizeStapA(i);
	}
	}
	}

	void RtpPacketizerH264::PacketizeFuA(size_t fragment_index) {
	// Fragment payload into packets (FU-A).
	// Strip out the original header and leave room for the FU-A header.
	const Fragment& fragment = input_fragments_[fragment_index];

	size_t fragment_length = fragment.length - kNalHeaderSize;
	size_t offset = kNalHeaderSize;
	size_t bytes_available = max_payload_len_ - kFuAHeaderSize;
	const size_t num_fragments =
	(fragment_length + (bytes_available - 1)) / bytes_available;

	const size_t avg_size = (fragment_length + num_fragments - 1) / num_fragments;
	while (fragment_length > 0) {
	size_t packet_length = avg_size;
	if (fragment_length < avg_size)
	packet_length = fragment_length;
	packets_.push(PacketUnit(Fragment(fragment.buffer + offset, packet_length),
	offset - kNalHeaderSize == 0,
	fragment_length == packet_length, false,
	fragment.buffer[0]));
	offset += packet_length;
	fragment_length -= packet_length;
	}
	RTC_CHECK_EQ(0u, fragment_length);
	}

	size_t RtpPacketizerH264::PacketizeStapA(size_t fragment_index) {
	// Aggregate fragments into one packet (STAP-A).
	size_t payload_size_left = max_payload_len_;
	int aggregated_fragments = 0;
	size_t fragment_headers_length = 0;
	const Fragment* fragment = &input_fragments_[fragment_index];
	RTC_CHECK_GE(payload_size_left, fragment->length);
	while (payload_size_left >= fragment->length + fragment_headers_length) {
	RTC_CHECK_GT(fragment->length, 0u);
	packets_.push(PacketUnit(*fragment, aggregated_fragments == 0, false, true,
	fragment->buffer[0]));
	payload_size_left -= fragment->length;
	payload_size_left -= fragment_headers_length;

	// Next fragment.
	++fragment_index;
	if (fragment_index == input_fragments_.size())
	break;
	fragment = &input_fragments_[fragment_index];

	fragment_headers_length = kLengthFieldSize;
	// If we are going to try to aggregate more fragments into this packet
	// we need to add the STAP-A NALU header and a length field for the first
	// NALU of this packet.
	if (aggregated_fragments == 0)
	fragment_headers_length += kNalHeaderSize + kLengthFieldSize;
	++aggregated_fragments;
	}
	packets_.back().last_fragment = true;
	return fragment_index;
	}

	bool RtpPacketizerH264::NextPacket(uint8_t* buffer,
	size_t* bytes_to_send,
	bool* last_packet) {
	*bytes_to_send = 0;
	if (packets_.empty()) {
	*bytes_to_send = 0;
	*last_packet = true;
	return false;
	}

	PacketUnit packet = packets_.front();

	if (packet.first_fragment && packet.last_fragment) {
	// Single NAL unit packet.
	*bytes_to_send = packet.source_fragment.length;
	memcpy(buffer, packet.source_fragment.buffer, *bytes_to_send);
	packets_.pop();
	input_fragments_.pop_front();
	RTC_CHECK_LE(*bytes_to_send, max_payload_len_);
	} else if (packet.aggregated) {
	NextAggregatePacket(buffer, bytes_to_send);
	RTC_CHECK_LE(*bytes_to_send, max_payload_len_);
	} else {
	NextFragmentPacket(buffer, bytes_to_send);
	RTC_CHECK_LE(*bytes_to_send, max_payload_len_);
	}
	*last_packet = packets_.empty();
	return true;
	}

	void RtpPacketizerH264::NextAggregatePacket(uint8_t* buffer,
	size_t* bytes_to_send) {
	PacketUnit* packet = &packets_.front();
	RTC_CHECK(packet->first_fragment);
	// STAP-A NALU header.
	buffer[0] = (packet->header & (kFBit \| kNriMask)) \| H264::NaluType::kStapA;
	int index = kNalHeaderSize;
	*bytes_to_send += kNalHeaderSize;
	while (packet->aggregated) {
	const Fragment& fragment = packet->source_fragment;
	// Add NAL unit length field.
	ByteWriter<uint16_t>::WriteBigEndian(&buffer[index], fragment.length);
	index += kLengthFieldSize;
	*bytes_to_send += kLengthFieldSize;
	// Add NAL unit.
	memcpy(&buffer[index], fragment.buffer, fragment.length);
	index += fragment.length;
	*bytes_to_send += fragment.length;
	packets_.pop();
	input_fragments_.pop_front();
	if (packet->last_fragment)
	break;
	packet = &packets_.front();
	}
	RTC_CHECK(packet->last_fragment);
	}

	void RtpPacketizerH264::NextFragmentPacket(uint8_t* buffer,
	size_t* bytes_to_send) {
	PacketUnit* packet = &packets_.front();
	// NAL unit fragmented over multiple packets (FU-A).
	// We do not send original NALU header, so it will be replaced by the
	// FU indicator header of the first packet.
	uint8_t fu_indicator =
	(packet->header & (kFBit \| kNriMask)) \| H264::NaluType::kFuA;
	uint8_t fu_header = 0;

	// S \| E \| R \| 5 bit type.
	fu_header \|= (packet->first_fragment ? kSBit : 0);
	fu_header \|= (packet->last_fragment ? kEBit : 0);
	uint8_t type = packet->header & kTypeMask;
	fu_header \|= type;
	buffer[0] = fu_indicator;
	buffer[1] = fu_header;

	const Fragment& fragment = packet->source_fragment;
	*bytes_to_send = fragment.length + kFuAHeaderSize;
	memcpy(buffer + kFuAHeaderSize, fragment.buffer, fragment.length);
	if (packet->last_fragment)
	input_fragments_.pop_front();
	packets_.pop();
	}

	ProtectionType RtpPacketizerH264::GetProtectionType() {
	return kProtectedPacket;
	}

	StorageType RtpPacketizerH264::GetStorageType(
	uint32_t retransmission_settings) {
	return kAllowRetransmission;
	}

	std::string RtpPacketizerH264::ToString() {
	return "RtpPacketizerH264";
	}

	RtpDepacketizerH264::RtpDepacketizerH264() : offset_(0), length_(0) {}
	RtpDepacketizerH264::~RtpDepacketizerH264() {}

	bool RtpDepacketizerH264::Parse(ParsedPayload* parsed_payload,
	const uint8_t* payload_data,
	size_t payload_data_length) {
	RTC_CHECK(parsed_payload != nullptr);
	if (payload_data_length == 0) {
	LOG(LS_ERROR) << "Empty payload.";
	return false;
	}

	offset_ = 0;
	length_ = payload_data_length;
	modified_buffer_.reset();

	uint8_t nal_type = payload_data[0] & kTypeMask;
	if (nal_type == H264::NaluType::kFuA) {
	// Fragmented NAL units (FU-A).
	if (!ParseFuaNalu(parsed_payload, payload_data))
	return false;
	} else {
	// We handle STAP-A and single NALU's the same way here. The jitter buffer
	// will depacketize the STAP-A into NAL units later.
	// TODO(sprang): Parse STAP-A offsets here and store in fragmentation vec.
	if (!ProcessStapAOrSingleNalu(parsed_payload, payload_data))
	return false;
	}

	const uint8_t* payload =
	modified_buffer_ ? modified_buffer_->data() : payload_data;

	parsed_payload->payload = payload + offset_;
	parsed_payload->payload_length = length_;
	return true;
	}

	bool RtpDepacketizerH264::ProcessStapAOrSingleNalu(
	ParsedPayload* parsed_payload,
	const uint8_t* payload_data) {
	parsed_payload->type.Video.width = 0;
	parsed_payload->type.Video.height = 0;
	parsed_payload->type.Video.codec = kRtpVideoH264;
	parsed_payload->type.Video.isFirstPacket = true;
	RTPVideoHeaderH264* h264_header =
	&parsed_payload->type.Video.codecHeader.H264;

	const uint8_t* nalu_start = payload_data + kNalHeaderSize;
	const size_t nalu_length = length_ - kNalHeaderSize;
	uint8_t nal_type = payload_data[0] & kTypeMask;
	std::vector<size_t> nalu_start_offsets;
	if (nal_type == H264::NaluType::kStapA) {
	// Skip the StapA header (StapA NAL type + length).
	if (length_ <= kStapAHeaderSize) {
	LOG(LS_ERROR) << "StapA header truncated.";
	return false;
	}

	if (!ParseStapAStartOffsets(nalu_start, nalu_length, &nalu_start_offsets)) {
	LOG(LS_ERROR) << "StapA packet with incorrect NALU packet lengths.";
	return false;
	}

	h264_header->packetization_type = kH264StapA;
	nal_type = payload_data[kStapAHeaderSize] & kTypeMask;
	} else {
	h264_header->packetization_type = kH264SingleNalu;
	nalu_start_offsets.push_back(0);
	}
	h264_header->nalu_type = nal_type;
	parsed_payload->frame_type = kVideoFrameDelta;

	nalu_start_offsets.push_back(length_ + kLengthFieldSize); // End offset.
	for (size_t i = 0; i < nalu_start_offsets.size() - 1; ++i) {
	size_t start_offset = nalu_start_offsets[i];
	// End offset is actually start offset for next unit, excluding length field
	// so remove that from this units length.
	size_t end_offset = nalu_start_offsets[i + 1] - kLengthFieldSize;
	if (end_offset - start_offset < H264::kNaluTypeSize) {
	LOG(LS_ERROR) << "STAP-A packet too short";
	return false;
	}

	nal_type = payload_data[start_offset] & kTypeMask;
	start_offset += H264::kNaluTypeSize;

	if (nal_type == H264::NaluType::kSps) {
	// Check if VUI is present in SPS and if it needs to be modified to avoid
	// excessive decoder latency.

	// Copy any previous data first (likely just the first header).
	std::unique_ptr<rtc::Buffer> output_buffer(new rtc::Buffer());
	if (start_offset)
	output_buffer->AppendData(payload_data, start_offset);

	// RBSP decode of payload data.
	std::unique_ptr<rtc::Buffer> rbsp_buffer = H264::ParseRbsp(
	&payload_data[start_offset], end_offset - start_offset);
	rtc::Optional<SpsParser::SpsState> sps;

	SpsVuiRewriter::ParseResult result = SpsVuiRewriter::ParseAndRewriteSps(
	rbsp_buffer->data(), rbsp_buffer->size(), &sps, output_buffer.get());
	switch (result) {
	case SpsVuiRewriter::ParseResult::kVuiRewritten:
	if (modified_buffer_) {
	LOG(LS_WARNING) << "More than one H264 SPS NAL units needing "
	"rewriting found within a single STAP-A packet. "
	"Keeping the first and rewriting the last.";
	}

	// Rewrite length field to new SPS size.
	if (h264_header->packetization_type == kH264StapA) {
	size_t length_field_offset =
	start_offset - (H264::kNaluTypeSize + kLengthFieldSize);
	// Stap-A Length includes payload data and type header.
	size_t rewritten_size =
	output_buffer->size() - start_offset + H264::kNaluTypeSize;
	ByteWriter<uint16_t>::WriteBigEndian(
	&(*output_buffer)[length_field_offset], rewritten_size);
	}

	// Append rest of packet.
	output_buffer->AppendData(&payload_data[end_offset],
	nalu_length + kNalHeaderSize - end_offset);

	modified_buffer_ = std::move(output_buffer);
	length_ = modified_buffer_->size();

	RTC_HISTOGRAM_ENUMERATION(kSpsValidHistogramName,
	SpsValidEvent::kReceivedSpsRewritten,
	SpsValidEvent::kSpsRewrittenMax);
	break;
	case SpsVuiRewriter::ParseResult::kPocOk:
	RTC_HISTOGRAM_ENUMERATION(kSpsValidHistogramName,
	SpsValidEvent::kReceivedSpsPocOk,
	SpsValidEvent::kSpsRewrittenMax);
	break;
	case SpsVuiRewriter::ParseResult::kVuiOk:
	RTC_HISTOGRAM_ENUMERATION(kSpsValidHistogramName,
	SpsValidEvent::kReceivedSpsVuiOk,
	SpsValidEvent::kSpsRewrittenMax);
	break;
	case SpsVuiRewriter::ParseResult::kFailure:
	RTC_HISTOGRAM_ENUMERATION(kSpsValidHistogramName,
	SpsValidEvent::kReceivedSpsParseFailure,
	SpsValidEvent::kSpsRewrittenMax);
	break;
	}

	if (sps) {
	parsed_payload->type.Video.width = sps->width;
	parsed_payload->type.Video.height = sps->height;
	}
	parsed_payload->frame_type = kVideoFrameKey;
	} else if (nal_type == H264::NaluType::kPps \|\|
	nal_type == H264::NaluType::kSei \|\|
	nal_type == H264::NaluType::kIdr) {
	parsed_payload->frame_type = kVideoFrameKey;
	}
	}

	return true;
	}

	bool RtpDepacketizerH264::ParseFuaNalu(
	RtpDepacketizer::ParsedPayload* parsed_payload,
	const uint8_t* payload_data) {
	if (length_ < kFuAHeaderSize) {
	LOG(LS_ERROR) << "FU-A NAL units truncated.";
	return false;
	}
	uint8_t fnri = payload_data[0] & (kFBit \| kNriMask);
	uint8_t original_nal_type = payload_data[1] & kTypeMask;
	bool first_fragment = (payload_data[1] & kSBit) > 0;

	if (first_fragment) {
	offset_ = 0;
	length_ -= kNalHeaderSize;
	uint8_t original_nal_header = fnri \| original_nal_type;
	modified_buffer_.reset(new rtc::Buffer());
	modified_buffer_->AppendData(payload_data + kNalHeaderSize, length_);
	(*modified_buffer_)[0] = original_nal_header;
	} else {
	offset_ = kFuAHeaderSize;
	length_ -= kFuAHeaderSize;
	}

	if (original_nal_type == H264::NaluType::kIdr) {
	parsed_payload->frame_type = kVideoFrameKey;
	} else {
	parsed_payload->frame_type = kVideoFrameDelta;
	}
	parsed_payload->type.Video.width = 0;
	parsed_payload->type.Video.height = 0;
	parsed_payload->type.Video.codec = kRtpVideoH264;
	parsed_payload->type.Video.isFirstPacket = first_fragment;
	RTPVideoHeaderH264* h264_header =
	&parsed_payload->type.Video.codecHeader.H264;
	h264_header->packetization_type = kH264FuA;
	h264_header->nalu_type = original_nal_type;
	return true;
	}

	} // namespace webrtc