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

 /*
  *  Copyright (c) 2012 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/rtp_rtcp/source/producer_fec.h"

 #include "modules/rtp_rtcp/source/forward_error_correction.h"
 #include "modules/rtp_rtcp/source/rtp_utility.h"

 namespace webrtc {

 enum { kREDForFECHeaderLength = 1 };
 // This controls the maximum amount of excess overhead (actual - target)
 // allowed in order to trigger GenerateFEC(), before |params_.max_fec_frames|
 // is reached. Overhead here is defined as relative to number of media packets.
 enum { kMaxExcessOverhead = 50 };  // Q8.
 // This is the minimum number of media packets required (above some protection
 // level) in order to trigger GenerateFEC(), before |params_.max_fec_frames| is
 // reached.
 enum { kMinimumMediaPackets = 4 };
 // Threshold on the received FEC protection level, above which we enforce at
 // least |kMinimumMediaPackets| packets for the FEC code. Below this
 // threshold |kMinimumMediaPackets| is set to default value of 1.
 enum { kHighProtectionThreshold = 80 };  // Corresponds to ~30 overhead, range
 // is 0 to 255, where 255 corresponds to 100% overhead (relative to number of
 // media packets).

 struct RtpPacket {
   WebRtc_UWord16 rtpHeaderLength;
   ForwardErrorCorrection::Packet* pkt;
 };

 RedPacket::RedPacket(int length)
     : data_(new uint8_t[length]),
       length_(length),
       header_length_(0) {
 }

 RedPacket::~RedPacket() {
   delete [] data_;
 }

 void RedPacket::CreateHeader(const uint8_t* rtp_header, int header_length,
                              int red_pl_type, int pl_type) {
   assert(header_length + kREDForFECHeaderLength <= length_);
   memcpy(data_, rtp_header, header_length);
   // Replace payload type.
   data_[1] &= 0x80;
   data_[1] += red_pl_type;
   // Add RED header
   // f-bit always 0
   data_[header_length] = pl_type;
   header_length_ = header_length + kREDForFECHeaderLength;
 }

 void RedPacket::SetSeqNum(int seq_num) {
   assert(seq_num >= 0 && seq_num < (1<<16));
   ModuleRTPUtility::AssignUWord16ToBuffer(&data_[2], seq_num);
 }

 void RedPacket::AssignPayload(const uint8_t* payload, int length) {
   assert(header_length_ + length <= length_);
   memcpy(data_ + header_length_, payload, length);
 }

 void RedPacket::ClearMarkerBit() {
   data_[1] &= 0x7F;
 }

 uint8_t* RedPacket::data() const {
   return data_;
 }

 int RedPacket::length() const {
   return length_;
 }

 ProducerFec::ProducerFec(ForwardErrorCorrection* fec)
     : fec_(fec),
       media_packets_fec_(),
       fec_packets_(),
       num_frames_(0),
       incomplete_frame_(false),
       num_first_partition_(0),
       minimum_media_packets_fec_(1),
       params_(),
       new_params_() {
   memset(&params_, 0, sizeof(params_));
   memset(&new_params_, 0, sizeof(new_params_));
 }

 ProducerFec::~ProducerFec() {
   DeletePackets();
 }

 void ProducerFec::SetFecParameters(const FecProtectionParams* params,
                                    int num_first_partition) {
   // Number of first partition packets cannot exceed kMaxMediaPackets
   assert(params->fec_rate >= 0 && params->fec_rate < 256);
   if (num_first_partition >
       static_cast<int>(ForwardErrorCorrection::kMaxMediaPackets)) {
       num_first_partition =
           ForwardErrorCorrection::kMaxMediaPackets;
   }
   // Store the new params and apply them for the next set of FEC packets being
   // produced.
   new_params_ = *params;
   num_first_partition_ = num_first_partition;
   if (params->fec_rate > kHighProtectionThreshold) {
     minimum_media_packets_fec_ = kMinimumMediaPackets;
   } else {
     minimum_media_packets_fec_ = 1;
   }
 }

 RedPacket* ProducerFec::BuildRedPacket(const uint8_t* data_buffer,
                                        int payload_length,
                                        int rtp_header_length,
                                        int red_pl_type) {
   RedPacket* red_packet = new RedPacket(payload_length +
                                         kREDForFECHeaderLength +
                                         rtp_header_length);
   int pl_type = data_buffer[1] & 0x7f;
   red_packet->CreateHeader(data_buffer, rtp_header_length,
                            red_pl_type, pl_type);
   red_packet->AssignPayload(data_buffer + rtp_header_length, payload_length);
   return red_packet;
 }

 int ProducerFec::AddRtpPacketAndGenerateFec(const uint8_t* data_buffer,
                                             int payload_length,
                                             int rtp_header_length) {
   assert(fec_packets_.empty());
   if (media_packets_fec_.empty()) {
     params_ = new_params_;
   }
   incomplete_frame_ = true;
   const bool marker_bit = (data_buffer[1] & kRtpMarkerBitMask) ? true : false;
   if (media_packets_fec_.size() < ForwardErrorCorrection::kMaxMediaPackets) {
     // Generic FEC can only protect up to kMaxMediaPackets packets.
     ForwardErrorCorrection::Packet* packet = new ForwardErrorCorrection::Packet;
     packet->length = payload_length + rtp_header_length;
     memcpy(packet->data, data_buffer, packet->length);
     media_packets_fec_.push_back(packet);
   }
   if (marker_bit) {
     ++num_frames_;
     incomplete_frame_ = false;
   }
   // Produce FEC over at most |params_.max_fec_frames| frames, or as soon as:
   // (1) the excess overhead (actual overhead - requested/target overhead) is
   // less than |kMaxExcessOverhead|, and
   // (2) at least |minimum_media_packets_fec_| media packets is reached.
   if (!incomplete_frame_ &&
       (num_frames_ == params_.max_fec_frames ||
           (ExcessOverheadBelowMax() && MinimumMediaPacketsReached()))) {
     assert(num_first_partition_ <=
            static_cast<int>(ForwardErrorCorrection::kMaxMediaPackets));
     int ret = fec_->GenerateFEC(media_packets_fec_,
                                 params_.fec_rate,
                                 num_first_partition_,
                                 params_.use_uep_protection,
                                 params_.fec_mask_type,
                                 &fec_packets_);
     if (fec_packets_.empty()) {
       num_frames_ = 0;
       DeletePackets();
     }
     return ret;
   }
   return 0;
 }

 // Returns true if the excess overhead (actual - target) for the FEC is below
 // the amount |kMaxExcessOverhead|. This effects the lower protection level
 // cases and low number of media packets/frame. The target overhead is given by
 // |params_.fec_rate|, and is only achievable in the limit of large number of
 // media packets.
 bool ProducerFec::ExcessOverheadBelowMax() {
   return ((Overhead() - params_.fec_rate) < kMaxExcessOverhead);
 }

 // Returns true if the media packet list for the FEC is at least
 // |minimum_media_packets_fec_|. This condition tries to capture the effect
 // that, for the same amount of protection/overhead, longer codes
 // (e.g. (2k,2m) vs (k,m)) are generally more effective at recovering losses.
 bool ProducerFec::MinimumMediaPacketsReached() {
   float avg_num_packets_frame = static_cast<float>(media_packets_fec_.size()) /
                                 num_frames_;
   if (avg_num_packets_frame < 2.0f) {
   return (static_cast<int>(media_packets_fec_.size()) >=
       minimum_media_packets_fec_);
   } else {
     // For larger rates (more packets/frame), increase the threshold.
     return (static_cast<int>(media_packets_fec_.size()) >=
         minimum_media_packets_fec_ + 1);
   }
 }

 bool ProducerFec::FecAvailable() const {
   return (fec_packets_.size() > 0);
 }

 RedPacket* ProducerFec::GetFecPacket(int red_pl_type,
                                      int fec_pl_type,
                                      uint16_t seq_num,
                                      int rtp_header_length) {
   if (fec_packets_.empty())
     return NULL;
   // Build FEC packet. The FEC packets in |fec_packets_| doesn't
   // have RTP headers, so we're reusing the header from the last
   // media packet.
   ForwardErrorCorrection::Packet* packet_to_send = fec_packets_.front();
   ForwardErrorCorrection::Packet* last_media_packet = media_packets_fec_.back();
   RedPacket* return_packet = new RedPacket(packet_to_send->length +
                                            kREDForFECHeaderLength +
                                            rtp_header_length);
   return_packet->CreateHeader(last_media_packet->data,
                               rtp_header_length,
                               red_pl_type,
                               fec_pl_type);
   return_packet->SetSeqNum(seq_num);
   return_packet->ClearMarkerBit();
   return_packet->AssignPayload(packet_to_send->data, packet_to_send->length);
   fec_packets_.pop_front();
   if (fec_packets_.empty()) {
     // Done with all the FEC packets. Reset for next run.
     DeletePackets();
     num_frames_ = 0;
   }
   return return_packet;
 }

 int ProducerFec::Overhead() const {
   // Overhead is defined as relative to the number of media packets, and not
   // relative to total number of packets. This definition is inhereted from the
   // protection factor produced by video_coding module and how the FEC
   // generation is implemented.
   assert(!media_packets_fec_.empty());
   int num_fec_packets = fec_->GetNumberOfFecPackets(media_packets_fec_.size(),
                                                     params_.fec_rate);
   // Return the overhead in Q8.
   return (num_fec_packets << 8) / media_packets_fec_.size();
 }

 void ProducerFec::DeletePackets() {
   while (!media_packets_fec_.empty()) {
     delete media_packets_fec_.front();
     media_packets_fec_.pop_front();
   }
   assert(media_packets_fec_.empty());
 }

 }  // namespace webrtc
	/*
	* Copyright (c) 2012 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/rtp_rtcp/source/producer_fec.h"

	#include "modules/rtp_rtcp/source/forward_error_correction.h"
	#include "modules/rtp_rtcp/source/rtp_utility.h"

	namespace webrtc {

	enum { kREDForFECHeaderLength = 1 };
	// This controls the maximum amount of excess overhead (actual - target)
	// allowed in order to trigger GenerateFEC(), before \|params_.max_fec_frames\|
	// is reached. Overhead here is defined as relative to number of media packets.
	enum { kMaxExcessOverhead = 50 }; // Q8.
	// This is the minimum number of media packets required (above some protection
	// level) in order to trigger GenerateFEC(), before \|params_.max_fec_frames\| is
	// reached.
	enum { kMinimumMediaPackets = 4 };
	// Threshold on the received FEC protection level, above which we enforce at
	// least \|kMinimumMediaPackets\| packets for the FEC code. Below this
	// threshold \|kMinimumMediaPackets\| is set to default value of 1.
	enum { kHighProtectionThreshold = 80 }; // Corresponds to ~30 overhead, range
	// is 0 to 255, where 255 corresponds to 100% overhead (relative to number of
	// media packets).

	struct RtpPacket {
	WebRtc_UWord16 rtpHeaderLength;
	ForwardErrorCorrection::Packet* pkt;
	};

	RedPacket::RedPacket(int length)
	: data_(new uint8_t[length]),
	length_(length),
	header_length_(0) {
	}

	RedPacket::~RedPacket() {
	delete [] data_;
	}

	void RedPacket::CreateHeader(const uint8_t* rtp_header, int header_length,
	int red_pl_type, int pl_type) {
	assert(header_length + kREDForFECHeaderLength <= length_);
	memcpy(data_, rtp_header, header_length);
	// Replace payload type.
	data_[1] &= 0x80;
	data_[1] += red_pl_type;
	// Add RED header
	// f-bit always 0
	data_[header_length] = pl_type;
	header_length_ = header_length + kREDForFECHeaderLength;
	}

	void RedPacket::SetSeqNum(int seq_num) {
	assert(seq_num >= 0 && seq_num < (1<<16));
	ModuleRTPUtility::AssignUWord16ToBuffer(&data_[2], seq_num);
	}

	void RedPacket::AssignPayload(const uint8_t* payload, int length) {
	assert(header_length_ + length <= length_);
	memcpy(data_ + header_length_, payload, length);
	}

	void RedPacket::ClearMarkerBit() {
	data_[1] &= 0x7F;
	}

	uint8_t* RedPacket::data() const {
	return data_;
	}

	int RedPacket::length() const {
	return length_;
	}

	ProducerFec::ProducerFec(ForwardErrorCorrection* fec)
	: fec_(fec),
	media_packets_fec_(),
	fec_packets_(),
	num_frames_(0),
	incomplete_frame_(false),
	num_first_partition_(0),
	minimum_media_packets_fec_(1),
	params_(),
	new_params_() {
	memset(&params_, 0, sizeof(params_));
	memset(&new_params_, 0, sizeof(new_params_));
	}

	ProducerFec::~ProducerFec() {
	DeletePackets();
	}

	void ProducerFec::SetFecParameters(const FecProtectionParams* params,
	int num_first_partition) {
	// Number of first partition packets cannot exceed kMaxMediaPackets
	assert(params->fec_rate >= 0 && params->fec_rate < 256);
	if (num_first_partition >
	static_cast<int>(ForwardErrorCorrection::kMaxMediaPackets)) {
	num_first_partition =
	ForwardErrorCorrection::kMaxMediaPackets;
	}
	// Store the new params and apply them for the next set of FEC packets being
	// produced.
	new_params_ = *params;
	num_first_partition_ = num_first_partition;
	if (params->fec_rate > kHighProtectionThreshold) {
	minimum_media_packets_fec_ = kMinimumMediaPackets;
	} else {
	minimum_media_packets_fec_ = 1;
	}
	}

	RedPacket* ProducerFec::BuildRedPacket(const uint8_t* data_buffer,
	int payload_length,
	int rtp_header_length,
	int red_pl_type) {
	RedPacket* red_packet = new RedPacket(payload_length +
	kREDForFECHeaderLength +
	rtp_header_length);
	int pl_type = data_buffer[1] & 0x7f;
	red_packet->CreateHeader(data_buffer, rtp_header_length,
	red_pl_type, pl_type);
	red_packet->AssignPayload(data_buffer + rtp_header_length, payload_length);
	return red_packet;
	}

	int ProducerFec::AddRtpPacketAndGenerateFec(const uint8_t* data_buffer,
	int payload_length,
	int rtp_header_length) {
	assert(fec_packets_.empty());
	if (media_packets_fec_.empty()) {
	params_ = new_params_;
	}
	incomplete_frame_ = true;
	const bool marker_bit = (data_buffer[1] & kRtpMarkerBitMask) ? true : false;
	if (media_packets_fec_.size() < ForwardErrorCorrection::kMaxMediaPackets) {
	// Generic FEC can only protect up to kMaxMediaPackets packets.
	ForwardErrorCorrection::Packet* packet = new ForwardErrorCorrection::Packet;
	packet->length = payload_length + rtp_header_length;
	memcpy(packet->data, data_buffer, packet->length);
	media_packets_fec_.push_back(packet);
	}
	if (marker_bit) {
	++num_frames_;
	incomplete_frame_ = false;
	}
	// Produce FEC over at most \|params_.max_fec_frames\| frames, or as soon as:
	// (1) the excess overhead (actual overhead - requested/target overhead) is
	// less than \|kMaxExcessOverhead\|, and
	// (2) at least \|minimum_media_packets_fec_\| media packets is reached.
	if (!incomplete_frame_ &&
	(num_frames_ == params_.max_fec_frames \|\|
	(ExcessOverheadBelowMax() && MinimumMediaPacketsReached()))) {
	assert(num_first_partition_ <=
	static_cast<int>(ForwardErrorCorrection::kMaxMediaPackets));
	int ret = fec_->GenerateFEC(media_packets_fec_,
	params_.fec_rate,
	num_first_partition_,
	params_.use_uep_protection,
	params_.fec_mask_type,
	&fec_packets_);
	if (fec_packets_.empty()) {
	num_frames_ = 0;
	DeletePackets();
	}
	return ret;
	}
	return 0;
	}

	// Returns true if the excess overhead (actual - target) for the FEC is below
	// the amount \|kMaxExcessOverhead\|. This effects the lower protection level
	// cases and low number of media packets/frame. The target overhead is given by
	// \|params_.fec_rate\|, and is only achievable in the limit of large number of
	// media packets.
	bool ProducerFec::ExcessOverheadBelowMax() {
	return ((Overhead() - params_.fec_rate) < kMaxExcessOverhead);
	}

	// Returns true if the media packet list for the FEC is at least
	// \|minimum_media_packets_fec_\|. This condition tries to capture the effect
	// that, for the same amount of protection/overhead, longer codes
	// (e.g. (2k,2m) vs (k,m)) are generally more effective at recovering losses.
	bool ProducerFec::MinimumMediaPacketsReached() {
	float avg_num_packets_frame = static_cast<float>(media_packets_fec_.size()) /
	num_frames_;
	if (avg_num_packets_frame < 2.0f) {
	return (static_cast<int>(media_packets_fec_.size()) >=
	minimum_media_packets_fec_);
	} else {
	// For larger rates (more packets/frame), increase the threshold.
	return (static_cast<int>(media_packets_fec_.size()) >=
	minimum_media_packets_fec_ + 1);
	}
	}

	bool ProducerFec::FecAvailable() const {
	return (fec_packets_.size() > 0);
	}

	RedPacket* ProducerFec::GetFecPacket(int red_pl_type,
	int fec_pl_type,
	uint16_t seq_num,
	int rtp_header_length) {
	if (fec_packets_.empty())
	return NULL;
	// Build FEC packet. The FEC packets in \|fec_packets_\| doesn't
	// have RTP headers, so we're reusing the header from the last
	// media packet.
	ForwardErrorCorrection::Packet* packet_to_send = fec_packets_.front();
	ForwardErrorCorrection::Packet* last_media_packet = media_packets_fec_.back();
	RedPacket* return_packet = new RedPacket(packet_to_send->length +
	kREDForFECHeaderLength +
	rtp_header_length);
	return_packet->CreateHeader(last_media_packet->data,
	rtp_header_length,
	red_pl_type,
	fec_pl_type);
	return_packet->SetSeqNum(seq_num);
	return_packet->ClearMarkerBit();
	return_packet->AssignPayload(packet_to_send->data, packet_to_send->length);
	fec_packets_.pop_front();
	if (fec_packets_.empty()) {
	// Done with all the FEC packets. Reset for next run.
	DeletePackets();
	num_frames_ = 0;
	}
	return return_packet;
	}

	int ProducerFec::Overhead() const {
	// Overhead is defined as relative to the number of media packets, and not
	// relative to total number of packets. This definition is inhereted from the
	// protection factor produced by video_coding module and how the FEC
	// generation is implemented.
	assert(!media_packets_fec_.empty());
	int num_fec_packets = fec_->GetNumberOfFecPackets(media_packets_fec_.size(),
	params_.fec_rate);
	// Return the overhead in Q8.
	return (num_fec_packets << 8) / media_packets_fec_.size();
	}

	void ProducerFec::DeletePackets() {
	while (!media_packets_fec_.empty()) {
	delete media_packets_fec_.front();
	media_packets_fec_.pop_front();
	}
	assert(media_packets_fec_.empty());
	}

	} // namespace webrtc