flexfec_header_reader_writer.cc | Explore in Territory

/*
 *  Copyright (c) 2023 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/flexfec_header_reader_writer.h"

#include <string.h>

#include "api/scoped_refptr.h"
#include "modules/rtp_rtcp/source/byte_io.h"
#include "modules/rtp_rtcp/source/forward_error_correction_internal.h"
#include "rtc_base/checks.h"
#include "rtc_base/logging.h"

namespace webrtc {

namespace {

// Maximum number of media packets that can be protected in one batch.
constexpr size_t kMaxMediaPackets = …;  // Since we are reusing ULPFEC masks.

// Maximum number of media packets tracked by FEC decoder.
// Maintain a sufficiently larger tracking window than `kMaxMediaPackets`
// to account for packet reordering in pacer/ network.
constexpr size_t kMaxTrackedMediaPackets = …;

// Maximum number of FEC packets stored inside ForwardErrorCorrection.
constexpr size_t kMaxFecPackets = …;

// Size (in bytes) of packet masks, given number of K bits set.
constexpr size_t kFlexfecPacketMaskSizes[] = …;

// Size (in bytes) of part of header which is not packet mask specific.
constexpr size_t kBaseHeaderSize = …;

// Size (in bytes) of part of header which is stream specific.
constexpr size_t kStreamSpecificHeaderSize = …;

// Size (in bytes) of header, given the single stream packet mask size, i.e.
// the number of K-bits set.
constexpr size_t kHeaderSizes[] = …;

// Here we count the K-bits as belonging to the packet mask.
// This can be used in conjunction with FlexfecHeaderWriter::MinPacketMaskSize,
// which calculates a bound on the needed packet mask size including K-bits,
// given a packet mask without K-bits.
size_t FlexfecHeaderSize(size_t packet_mask_size) { … }

}  // namespace

FlexfecHeaderReader::FlexfecHeaderReader()
    : … { … }

FlexfecHeaderReader::~FlexfecHeaderReader() = default;

// TODO(brandtr): Update this function when we support flexible masks,
// and retransmissions.
bool FlexfecHeaderReader::ReadFecHeader(
    ForwardErrorCorrection::ReceivedFecPacket* fec_packet) const { … }

FlexfecHeaderWriter::FlexfecHeaderWriter()
    : … { … }

FlexfecHeaderWriter::~FlexfecHeaderWriter() = default;

size_t FlexfecHeaderWriter::MinPacketMaskSize(const uint8_t* packet_mask,
                                              size_t packet_mask_size) const { … }

size_t FlexfecHeaderWriter::FecHeaderSize(size_t packet_mask_size) const { … }

// This function adapts the precomputed ULPFEC packet masks to the
// FlexFEC header standard. Note that the header size is computed by
// FecHeaderSize(), so in this function we can be sure that we are
// writing in space that is intended for the header.
//
// TODO(brandtr): Update this function when we support offset-based masks
// and retransmissions.
void FlexfecHeaderWriter::FinalizeFecHeader(
    rtc::ArrayView<const ProtectedStream> protected_streams,
    ForwardErrorCorrection::Packet& fec_packet) const { … }

}  // namespace webrtc
chromium/third_party/webrtc/modules/rtp_rtcp/source/flexfec_header_reader_writer.cc
