Quelle  media_session.cc   Sprache: C

/*
 *  Copyright 2004 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 "pc/media_session.h"

#include <stddef.h>

#include <algorithm>
#include <map>
#include <memory>
#include <optional>
#include <string>
#include <unordered_map>
#include <utility>
#include <vector>

#include "absl/algorithm/container.h"
#include "absl/strings/match.h"
#include "absl/strings/string_view.h"
#include "api/field_trials_view.h"
#include "api/media_types.h"
#include "api/rtc_error.h"
#include "api/rtp_parameters.h"
#include "api/rtp_transceiver_direction.h"
#include "call/payload_type.h"
#include "media/base/codec.h"
#include "media/base/codec_comparators.h"
#include "media/base/media_constants.h"
#include "media/base/media_engine.h"
#include "media/base/rid_description.h"
#include "media/base/sdp_video_format_utils.h"
#include "media/base/stream_params.h"
#include "media/sctp/sctp_transport_internal.h"
#include "p2p/base/ice_credentials_iterator.h"
#include "p2p/base/p2p_constants.h"
#include "p2p/base/transport_description.h"
#include "p2p/base/transport_description_factory.h"
#include "p2p/base/transport_info.h"
#include "pc/media_protocol_names.h"
#include "pc/rtp_media_utils.h"
#include "pc/session_description.h"
#include "pc/simulcast_description.h"
#include "pc/used_ids.h"
#include "rtc_base/checks.h"
#include "rtc_base/logging.h"
#include "rtc_base/string_encode.h"
#include "rtc_base/strings/string_builder.h"
#include "rtc_base/unique_id_generator.h"

namespace {

using rtc::UniqueRandomIdGenerator;
using webrtc::RTCError;
using webrtc::RTCErrorType;
using webrtc::RtpTransceiverDirection;

webrtc::RtpExtension RtpExtensionFromCapability(
    const webrtc::RtpHeaderExtensionCapability& capability) {
  return webrtc::RtpExtension(capability.uri,
                              capability.preferred_id.value_or(1),
                              capability.preferred_encrypt);
}

cricket::RtpHeaderExtensions RtpHeaderExtensionsFromCapabilities(
    const std::vector<webrtc::RtpHeaderExtensionCapability>& capabilities) {
  cricket::RtpHeaderExtensions exts;
  for (const auto& capability : capabilities) {
    exts.push_back(RtpExtensionFromCapability(capability));
  }
  return exts;
}

std::vector<webrtc::RtpHeaderExtensionCapability>
UnstoppedRtpHeaderExtensionCapabilities(
    std::vector<webrtc::RtpHeaderExtensionCapability> capabilities) {
  capabilities.erase(
      std::remove_if(
          capabilities.begin(), capabilities.end(),
          [](const webrtc::RtpHeaderExtensionCapability& capability) {
            return capability.direction == RtpTransceiverDirection::kStopped;
          }),
      capabilities.end());
  return capabilities;
}

bool IsCapabilityPresent(const webrtc::RtpHeaderExtensionCapability& capability,
                         const cricket::RtpHeaderExtensions& extensions) {
  return std::find_if(extensions.begin(), extensions.end(),
                      [&capability](const webrtc::RtpExtension& extension) {
                        return capability.uri == extension.uri;
                      }) != extensions.end();
}

cricket::RtpHeaderExtensions UnstoppedOrPresentRtpHeaderExtensions(
    const std::vector<webrtc::RtpHeaderExtensionCapability>& capabilities,
    const cricket::RtpHeaderExtensions& all_encountered_extensions) {
  cricket::RtpHeaderExtensions extensions;
  for (const auto& capability : capabilities) {
    if (capability.direction != RtpTransceiverDirection::kStopped ||
        IsCapabilityPresent(capability, all_encountered_extensions)) {
      extensions.push_back(RtpExtensionFromCapability(capability));
    }
  }
  return extensions;
}

}  // namespace

namespace cricket {

namespace {

bool IsRtxCodec(const webrtc::RtpCodecCapability& capability) {
  return absl::EqualsIgnoreCase(capability.name, kRtxCodecName);
}

bool ContainsRtxCodec(const std::vector<Codec>& codecs) {
  return absl::c_find_if(codecs, [](const Codec& c) {
           return c.GetResiliencyType() == Codec::ResiliencyType::kRtx;
         }) != codecs.end();
}

bool IsRedCodec(const webrtc::RtpCodecCapability& capability) {
  return absl::EqualsIgnoreCase(capability.name, kRedCodecName);
}

bool ContainsFlexfecCodec(const std::vector<Codec>& codecs) {
  return absl::c_find_if(codecs, [](const Codec& c) {
           return c.GetResiliencyType() == Codec::ResiliencyType::kFlexfec;
         }) != codecs.end();
}

bool IsComfortNoiseCodec(const Codec& codec) {
  return absl::EqualsIgnoreCase(codec.name, kComfortNoiseCodecName);
}

void StripCNCodecs(Codecs* audio_codecs) {
  audio_codecs->erase(std::remove_if(audio_codecs->begin(), audio_codecs->end(),
                                     [](const Codec& codec) {
                                       return IsComfortNoiseCodec(codec);
                                     }),
                      audio_codecs->end());
}

RtpTransceiverDirection NegotiateRtpTransceiverDirection(
    RtpTransceiverDirection offer,
    RtpTransceiverDirection wants) {
  bool offer_send = webrtc::RtpTransceiverDirectionHasSend(offer);
  bool offer_recv = webrtc::RtpTransceiverDirectionHasRecv(offer);
  bool wants_send = webrtc::RtpTransceiverDirectionHasSend(wants);
  bool wants_recv = webrtc::RtpTransceiverDirectionHasRecv(wants);
  return webrtc::RtpTransceiverDirectionFromSendRecv(offer_recv && wants_send,
                                                     offer_send && wants_recv);
}

bool IsMediaContentOfType(const ContentInfo* content, MediaType media_type) {
  if (!content || !content->media_description()) {
    return false;
  }
  return content->media_description()->type() == media_type;
}

// Finds all StreamParams of all media types and attach them to stream_params.
StreamParamsVec GetCurrentStreamParams(
    const std::vector<const ContentInfo*>& active_local_contents) {
  StreamParamsVec stream_params;
  for (const ContentInfo* content : active_local_contents) {
    for (const StreamParams& params : content->media_description()->streams()) {
      stream_params.push_back(params);
    }
  }
  return stream_params;
}

StreamParams CreateStreamParamsForNewSenderWithSsrcs(
    const SenderOptions& sender,
    const std::string& rtcp_cname,
    bool include_rtx_streams,
    bool include_flexfec_stream,
    UniqueRandomIdGenerator* ssrc_generator,
    const webrtc::FieldTrialsView& field_trials) {
  StreamParams result;
  result.id = sender.track_id;

  // TODO(brandtr): Update when we support multistream protection.
  if (include_flexfec_stream && sender.num_sim_layers > 1) {
    include_flexfec_stream = false;
    RTC_LOG(LS_WARNING)
        << "Our FlexFEC implementation only supports protecting "
           "a single media streams. This session has multiple "
           "media streams however, so no FlexFEC SSRC will be generated.";
  }
  if (include_flexfec_stream && !field_trials.IsEnabled("WebRTC-FlexFEC-03")) {
    include_flexfec_stream = false;
    RTC_LOG(LS_WARNING)
        << "WebRTC-FlexFEC trial is not enabled, not sending FlexFEC";
  }

  result.GenerateSsrcs(sender.num_sim_layers, include_rtx_streams,
                       include_flexfec_stream, ssrc_generator);

  result.cname = rtcp_cname;
  result.set_stream_ids(sender.stream_ids);

  return result;
}

bool ValidateSimulcastLayers(const std::vector<RidDescription>& rids,
                             const SimulcastLayerList& simulcast_layers) {
  return absl::c_all_of(
      simulcast_layers.GetAllLayers(), [&rids](const SimulcastLayer& layer) {
        return absl::c_any_of(rids, [&layer](const RidDescription& rid) {
          return rid.rid == layer.rid;
        });
      });
}

StreamParams CreateStreamParamsForNewSenderWithRids(
    const SenderOptions& sender,
    const std::string& rtcp_cname) {
  RTC_DCHECK(!sender.rids.empty());
  RTC_DCHECK_EQ(sender.num_sim_layers, 0)
      << "RIDs are the compliant way to indicate simulcast.";
  RTC_DCHECK(ValidateSimulcastLayers(sender.rids, sender.simulcast_layers));
  StreamParams result;
  result.id = sender.track_id;
  result.cname = rtcp_cname;
  result.set_stream_ids(sender.stream_ids);

  // More than one rid should be signaled.
  if (sender.rids.size() > 1) {
    result.set_rids(sender.rids);
  }

  return result;
}

// Adds SimulcastDescription if indicated by the media description options.
// MediaContentDescription should already be set up with the send rids.
void AddSimulcastToMediaDescription(
    const MediaDescriptionOptions& media_description_options,
    MediaContentDescription* description) {
  RTC_DCHECK(description);

  // Check if we are using RIDs in this scenario.
  if (absl::c_all_of(description->streams(), [](const StreamParams& params) {
        return !params.has_rids();
      })) {
    return;
  }

  RTC_DCHECK_EQ(1, description->streams().size())
      << "RIDs are only supported in Unified Plan semantics.";
  RTC_DCHECK_EQ(1, media_description_options.sender_options.size());
  RTC_DCHECK(description->type() == MediaType::MEDIA_TYPE_AUDIO ||
             description->type() == MediaType::MEDIA_TYPE_VIDEO);

  // One RID or less indicates that simulcast is not needed.
  if (description->streams()[0].rids().size() <= 1) {
    return;
  }

  // Only negotiate the send layers.
  SimulcastDescription simulcast;
  simulcast.send_layers() =
      media_description_options.sender_options[0].simulcast_layers;
  description->set_simulcast_description(simulcast);
}

// Adds a StreamParams for each SenderOptions in `sender_options` to
// content_description.
// `current_params` - All currently known StreamParams of any media type.
bool AddStreamParams(const std::vector<SenderOptions>& sender_options,
                     const std::string& rtcp_cname,
                     UniqueRandomIdGenerator* ssrc_generator,
                     StreamParamsVec* current_streams,
                     MediaContentDescription* content_description,
                     const webrtc::FieldTrialsView& field_trials) {
  // SCTP streams are not negotiated using SDP/ContentDescriptions.
  if (IsSctpProtocol(content_description->protocol())) {
    return true;
  }

  const bool include_rtx_streams =
      ContainsRtxCodec(content_description->codecs());

  const bool include_flexfec_stream =
      ContainsFlexfecCodec(content_description->codecs());

  for (const SenderOptions& sender : sender_options) {
    StreamParams* param = GetStreamByIds(*current_streams, sender.track_id);
    if (!param) {
      // This is a new sender.
      StreamParams stream_param =
          sender.rids.empty()
              ?
              // Signal SSRCs and legacy simulcast (if requested).
              CreateStreamParamsForNewSenderWithSsrcs(
                  sender, rtcp_cname, include_rtx_streams,
                  include_flexfec_stream, ssrc_generator, field_trials)
              :
              // Signal RIDs and spec-compliant simulcast (if requested).
              CreateStreamParamsForNewSenderWithRids(sender, rtcp_cname);

      content_description->AddStream(stream_param);

      // Store the new StreamParams in current_streams.
      // This is necessary so that we can use the CNAME for other media types.
      current_streams->push_back(stream_param);
    } else {
      // Use existing generated SSRCs/groups, but update the sync_label if
      // necessary. This may be needed if a MediaStreamTrack was moved from one
      // MediaStream to another.
      param->set_stream_ids(sender.stream_ids);
      content_description->AddStream(*param);
    }
  }
  return true;
}

// Updates the transport infos of the `sdesc` according to the given
// `bundle_group`. The transport infos of the content names within the
// `bundle_group` should be updated to use the ufrag, pwd and DTLS role of the
// first content within the `bundle_group`.
bool UpdateTransportInfoForBundle(const ContentGroup& bundle_group,
                                  SessionDescription* sdesc) {
  // The bundle should not be empty.
  if (!sdesc || !bundle_group.FirstContentName()) {
    return false;
  }

  // We should definitely have a transport for the first content.
  const std::string& selected_content_name = *bundle_group.FirstContentName();
  const TransportInfo* selected_transport_info =
      sdesc->GetTransportInfoByName(selected_content_name);
  if (!selected_transport_info) {
    return false;
  }

  // Set the other contents to use the same ICE credentials.
  const std::string& selected_ufrag =
      selected_transport_info->description.ice_ufrag;
  const std::string& selected_pwd =
      selected_transport_info->description.ice_pwd;
  ConnectionRole selected_connection_role =
      selected_transport_info->description.connection_role;
  for (TransportInfo& transport_info : sdesc->transport_infos()) {
    if (bundle_group.HasContentName(transport_info.content_name) &&
        transport_info.content_name != selected_content_name) {
      transport_info.description.ice_ufrag = selected_ufrag;
      transport_info.description.ice_pwd = selected_pwd;
      transport_info.description.connection_role = selected_connection_role;
    }
  }
  return true;
}

std::vector<const ContentInfo*> GetActiveContents(
    const SessionDescription& description,
    const MediaSessionOptions& session_options) {
  std::vector<const ContentInfo*> active_contents;
  for (size_t i = 0; i < description.contents().size(); ++i) {
    RTC_DCHECK_LT(i, session_options.media_description_options.size());
    const ContentInfo& content = description.contents()[i];
    const MediaDescriptionOptions& media_options =
        session_options.media_description_options[i];
    if (!content.rejected && !media_options.stopped &&
        content.name == media_options.mid) {
      active_contents.push_back(&content);
    }
  }
  return active_contents;
}

// Create a media content to be offered for the given `sender_options`,
// according to the given options.rtcp_mux, session_options.is_muc, codecs,
// secure_transport, crypto, and current_streams. If we don't currently have
// crypto (in current_cryptos) and it is enabled (in secure_policy), crypto is
// created (according to crypto_suites). The created content is added to the
// offer.
RTCError CreateContentOffer(
    const MediaDescriptionOptions& media_description_options,
    const MediaSessionOptions& session_options,
    const RtpHeaderExtensions& rtp_extensions,
    UniqueRandomIdGenerator* ssrc_generator,
    StreamParamsVec* current_streams,
    MediaContentDescription* offer) {
  offer->set_rtcp_mux(session_options.rtcp_mux_enabled);
  offer->set_rtcp_reduced_size(true);

  // Build the vector of header extensions with directions for this
  // media_description's options.
  RtpHeaderExtensions extensions;
  for (const auto& extension_with_id : rtp_extensions) {
    for (const auto& extension : media_description_options.header_extensions) {
      if (extension_with_id.uri == extension.uri &&
          extension_with_id.encrypt == extension.preferred_encrypt) {
        // TODO(crbug.com/1051821): Configure the extension direction from
        // the information in the media_description_options extension
        // capability.
        if (extension.direction != RtpTransceiverDirection::kStopped) {
          extensions.push_back(extension_with_id);
        }
      }
    }
  }
  offer->set_rtp_header_extensions(extensions);

  AddSimulcastToMediaDescription(media_description_options, offer);

  return RTCError::OK();
}

RTCError CreateMediaContentOffer(
    const MediaDescriptionOptions& media_description_options,
    const MediaSessionOptions& session_options,
    const std::vector<Codec>& codecs,
    const RtpHeaderExtensions& rtp_extensions,
    UniqueRandomIdGenerator* ssrc_generator,
    StreamParamsVec* current_streams,
    MediaContentDescription* offer,
    const webrtc::FieldTrialsView& field_trials) {
  offer->AddCodecs(codecs);
  if (!AddStreamParams(media_description_options.sender_options,
                       session_options.rtcp_cname, ssrc_generator,
                       current_streams, offer, field_trials)) {
    LOG_AND_RETURN_ERROR(RTCErrorType::INTERNAL_ERROR,
                         "Failed to add stream parameters");
  }

  return CreateContentOffer(media_description_options, session_options,
                            rtp_extensions, ssrc_generator, current_streams,
                            offer);
}

void NegotiatePacketization(const Codec& local_codec,
                            const Codec& remote_codec,
                            Codec* negotiated_codec) {
  negotiated_codec->packetization =
      (local_codec.packetization == remote_codec.packetization)
          ? local_codec.packetization
          : std::nullopt;
}

#ifdef RTC_ENABLE_H265
void NegotiateTxMode(const Codec& local_codec,
                     const Codec& remote_codec,
                     Codec* negotiated_codec) {
  negotiated_codec->tx_mode = (local_codec.tx_mode == remote_codec.tx_mode)
                                  ? local_codec.tx_mode
                                  : std::nullopt;
}
#endif

// Update the ID fields of the codec vector.
// If any codec has an ID with value "kIdNotSet", use the payload type suggester
// to assign and record a payload type for it.
// If there is a RED codec without its fmtp parameter, give it the ID of the
// first OPUS codec in the codec list.
webrtc::RTCError AssignCodecIdsAndLinkRed(
    webrtc::PayloadTypeSuggester* pt_suggester,
    const std::string& mid,
    std::vector<Codec>& codecs) {
  int opus_codec = Codec::kIdNotSet;
  for (cricket::Codec& codec : codecs) {
    if (codec.id == Codec::kIdNotSet) {
      // Add payload types to codecs, if needed
      // This should only happen if WebRTC-PayloadTypesInTransport field trial
      // is enabled.
      RTC_CHECK(pt_suggester);
      auto result = pt_suggester->SuggestPayloadType(mid, codec);
      if (!result.ok()) {
        return result.error();
      }
      codec.id = result.value();
    }
    // record first Opus codec id
    if (absl::EqualsIgnoreCase(codec.name, kOpusCodecName) &&
        opus_codec == Codec::kIdNotSet) {
      opus_codec = codec.id;
    }
  }
  if (opus_codec != Codec::kIdNotSet) {
    for (cricket::Codec& codec : codecs) {
      if (codec.type == Codec::Type::kAudio &&
          absl::EqualsIgnoreCase(codec.name, kRedCodecName)) {
        if (codec.params.empty()) {
          char buffer[100];
          rtc::SimpleStringBuilder param(buffer);
          param << opus_codec << "/" << opus_codec;
          RTC_LOG(LS_ERROR) << "DEBUG: Setting RED param to " << param.str();
          codec.SetParam(kCodecParamNotInNameValueFormat, param.str());
        }
      }
    }
  }
  return webrtc::RTCError::OK();
}

void NegotiateCodecs(const std::vector<Codec>& local_codecs,
                     const std::vector<Codec>& offered_codecs,
                     std::vector<Codec>* negotiated_codecs,
                     bool keep_offer_order) {
  for (const Codec& ours : local_codecs) {
    std::optional<Codec> theirs =
        webrtc::FindMatchingCodec(local_codecs, offered_codecs, ours);
    // Note that we intentionally only find one matching codec for each of our
    // local codecs, in case the remote offer contains duplicate codecs.
    if (theirs) {
      Codec negotiated = ours;
      NegotiatePacketization(ours, *theirs, &negotiated);
      negotiated.IntersectFeedbackParams(*theirs);
      if (negotiated.GetResiliencyType() == Codec::ResiliencyType::kRtx) {
        const auto apt_it =
            theirs->params.find(kCodecParamAssociatedPayloadType);
        // webrtc::FindMatchingCodec shouldn't return something with no apt
        // value.
        RTC_DCHECK(apt_it != theirs->params.end());
        negotiated.SetParam(kCodecParamAssociatedPayloadType, apt_it->second);

        // We support parsing the declarative rtx-time parameter.
        const auto rtx_time_it = theirs->params.find(kCodecParamRtxTime);
        if (rtx_time_it != theirs->params.end()) {
          negotiated.SetParam(kCodecParamRtxTime, rtx_time_it->second);
        }
      } else if (negotiated.GetResiliencyType() ==
                 Codec::ResiliencyType::kRed) {
        const auto red_it =
            theirs->params.find(kCodecParamNotInNameValueFormat);
        if (red_it != theirs->params.end()) {
          negotiated.SetParam(kCodecParamNotInNameValueFormat, red_it->second);
        }
      }
      if (absl::EqualsIgnoreCase(ours.name, kH264CodecName)) {
        webrtc::H264GenerateProfileLevelIdForAnswer(ours.params, theirs->params,
                                                    &negotiated.params);
      }
#ifdef RTC_ENABLE_H265
      if (absl::EqualsIgnoreCase(ours.name, kH265CodecName)) {
        webrtc::H265GenerateProfileTierLevelForAnswer(
            ours.params, theirs->params, &negotiated.params);
        NegotiateTxMode(ours, *theirs, &negotiated);
      }
#endif
      negotiated.id = theirs->id;
      negotiated.name = theirs->name;
      negotiated_codecs->push_back(std::move(negotiated));
    }
  }
  if (keep_offer_order) {
    // RFC3264: Although the answerer MAY list the formats in their desired
    // order of preference, it is RECOMMENDED that unless there is a
    // specific reason, the answerer list formats in the same relative order
    // they were present in the offer.
    // This can be skipped when the transceiver has any codec preferences.
    std::unordered_map<int, int> payload_type_preferences;
    int preference = static_cast<int>(offered_codecs.size() + 1);
    for (const Codec& codec : offered_codecs) {
      payload_type_preferences[codec.id] = preference--;
    }
    absl::c_sort(*negotiated_codecs, [&payload_type_preferences](
                                         const Codec& a, const Codec& b) {
      return payload_type_preferences[a.id] > payload_type_preferences[b.id];
    });
  }
}

// Find the codec in `codec_list` that `rtx_codec` is associated with.
const Codec* GetAssociatedCodecForRtx(const std::vector<Codec>& codec_list,
                                      const Codec& rtx_codec) {
  std::string associated_pt_str;
  if (!rtx_codec.GetParam(kCodecParamAssociatedPayloadType,
                          &associated_pt_str)) {
    RTC_LOG(LS_WARNING) << "RTX codec " << rtx_codec.id
                        << " is missing an associated payload type.";
    return nullptr;
  }

  int associated_pt;
  if (!rtc::FromString(associated_pt_str, &associated_pt)) {
    RTC_LOG(LS_WARNING) << "Couldn't convert payload type " << associated_pt_str
                        << " of RTX codec " << rtx_codec.id
                        << " to an integer.";
    return nullptr;
  }

  // Find the associated codec for the RTX codec.
  const Codec* associated_codec = FindCodecById(codec_list, associated_pt);
  if (!associated_codec) {
    RTC_LOG(LS_WARNING) << "Couldn't find associated codec with payload type "
                        << associated_pt << " for RTX codec " << rtx_codec.id
                        << ".";
  }
  return associated_codec;
}

// Find the codec in `codec_list` that `red_codec` is associated with.
const Codec* GetAssociatedCodecForRed(const std::vector<Codec>& codec_list,
                                      const Codec& red_codec) {
  std::string fmtp;
  if (!red_codec.GetParam(kCodecParamNotInNameValueFormat, &fmtp)) {
    // Don't log for video/RED where this is normal.
    if (red_codec.type == Codec::Type::kAudio) {
      RTC_LOG(LS_WARNING) << "RED codec " << red_codec.id
                          << " is missing an associated payload type.";
    }
    return nullptr;
  }

  std::vector<absl::string_view> redundant_payloads = rtc::split(fmtp, '/');
  if (redundant_payloads.size() < 2) {
    return nullptr;
  }

  absl::string_view associated_pt_str = redundant_payloads[0];
  int associated_pt;
  if (!rtc::FromString(associated_pt_str, &associated_pt)) {
    RTC_LOG(LS_WARNING) << "Couldn't convert first payload type "
                        << associated_pt_str << " of RED codec " << red_codec.id
                        << " to an integer.";
    return nullptr;
  }

  // Find the associated codec for the RED codec.
  const Codec* associated_codec = FindCodecById(codec_list, associated_pt);
  if (!associated_codec) {
    RTC_LOG(LS_WARNING) << "Couldn't find associated codec with payload type "
                        << associated_pt << " for RED codec " << red_codec.id
                        << ".";
  }
  return associated_codec;
}

// Adds all codecs from `reference_codecs` to `offered_codecs` that don't
// already exist in `offered_codecs` and ensure the payload types don't
// collide.
void MergeCodecs(const std::vector<Codec>& reference_codecs,
                 std::vector<Codec>* offered_codecs,
                 UsedPayloadTypes* used_pltypes) {
  // Add all new codecs that are not RTX/RED codecs.
  // The two-pass splitting of the loops means preferring payload types
  // of actual codecs with respect to collisions.
  for (const Codec& reference_codec : reference_codecs) {
    if (reference_codec.GetResiliencyType() != Codec::ResiliencyType::kRtx &&
        reference_codec.GetResiliencyType() != Codec::ResiliencyType::kRed &&
        !webrtc::FindMatchingCodec(reference_codecs, *offered_codecs,
                                   reference_codec)) {
      Codec codec = reference_codec;
      used_pltypes->FindAndSetIdUsed(&codec);
      offered_codecs->push_back(codec);
    }
  }

  // Add all new RTX or RED codecs.
  for (const Codec& reference_codec : reference_codecs) {
    if (reference_codec.GetResiliencyType() == Codec::ResiliencyType::kRtx &&
        !webrtc::FindMatchingCodec(reference_codecs, *offered_codecs,
                                   reference_codec)) {
      Codec rtx_codec = reference_codec;
      const Codec* associated_codec =
          GetAssociatedCodecForRtx(reference_codecs, rtx_codec);
      if (!associated_codec) {
        continue;
      }
      // Find a codec in the offered list that matches the reference codec.
      // Its payload type may be different than the reference codec.
      std::optional<Codec> matching_codec = webrtc::FindMatchingCodec(
          reference_codecs, *offered_codecs, *associated_codec);
      if (!matching_codec) {
        RTC_LOG(LS_WARNING)
            << "Couldn't find matching " << associated_codec->name << " codec.";
        continue;
      }

      rtx_codec.params[kCodecParamAssociatedPayloadType] =
          rtc::ToString(matching_codec->id);
      used_pltypes->FindAndSetIdUsed(&rtx_codec);
      offered_codecs->push_back(rtx_codec);
    } else if (reference_codec.GetResiliencyType() ==
                   Codec::ResiliencyType::kRed &&
               !webrtc::FindMatchingCodec(reference_codecs, *offered_codecs,
                                          reference_codec)) {
      Codec red_codec = reference_codec;
      const Codec* associated_codec =
          GetAssociatedCodecForRed(reference_codecs, red_codec);
      if (associated_codec) {
        std::optional<Codec> matching_codec = webrtc::FindMatchingCodec(
            reference_codecs, *offered_codecs, *associated_codec);
        if (!matching_codec) {
          RTC_LOG(LS_WARNING) << "Couldn't find matching "
                              << associated_codec->name << " codec.";
          continue;
        }

        red_codec.params[kCodecParamNotInNameValueFormat] =
            rtc::ToString(matching_codec->id) + "/" +
            rtc::ToString(matching_codec->id);
      }
      used_pltypes->FindAndSetIdUsed(&red_codec);
      offered_codecs->push_back(red_codec);
    }
  }
}

// `codecs` is a full list of codecs with correct payload type mappings, which
// don't conflict with mappings of the other media type; `supported_codecs` is
// a list filtered for the media section`s direction but with default payload
// types.
std::vector<Codec> MatchCodecPreference(
    const std::vector<webrtc::RtpCodecCapability>& codec_preferences,
    const std::vector<Codec>& codecs,
    const std::vector<Codec>& supported_codecs) {
  std::vector<Codec> filtered_codecs;
  bool want_rtx = false;
  bool want_red = false;

  for (const auto& codec_preference : codec_preferences) {
    if (IsRtxCodec(codec_preference)) {
      want_rtx = true;
    } else if (IsRedCodec(codec_preference)) {
      want_red = true;
    }
  }
  bool red_was_added = false;
  for (const auto& codec_preference : codec_preferences) {
    auto found_codec = absl::c_find_if(
        supported_codecs, [&codec_preference](const Codec& codec) {
          webrtc::RtpCodecParameters codec_parameters =
              codec.ToCodecParameters();
          return codec_parameters.name == codec_preference.name &&
                 codec_parameters.kind == codec_preference.kind &&
                 codec_parameters.num_channels ==
                     codec_preference.num_channels &&
                 codec_parameters.clock_rate == codec_preference.clock_rate &&
                 codec_parameters.parameters == codec_preference.parameters;
        });

    if (found_codec != supported_codecs.end()) {
      std::optional<Codec> found_codec_with_correct_pt =
          webrtc::FindMatchingCodec(supported_codecs, codecs, *found_codec);
      if (found_codec_with_correct_pt) {
        // RED may already have been added if its primary codec is before RED
        // in the codec list.
        bool is_red_codec = found_codec_with_correct_pt->GetResiliencyType() ==
                            Codec::ResiliencyType::kRed;
        if (!is_red_codec || !red_was_added) {
          filtered_codecs.push_back(*found_codec_with_correct_pt);
          red_was_added = is_red_codec ? true : red_was_added;
        }
        std::string id = rtc::ToString(found_codec_with_correct_pt->id);
        // Search for the matching rtx or red codec.
        if (want_red || want_rtx) {
          for (const auto& codec : codecs) {
            if (codec.GetResiliencyType() == Codec::ResiliencyType::kRtx) {
              const auto apt =
                  codec.params.find(cricket::kCodecParamAssociatedPayloadType);
              if (apt != codec.params.end() && apt->second == id) {
                filtered_codecs.push_back(codec);
                break;
              }
            } else if (codec.GetResiliencyType() ==
                       Codec::ResiliencyType::kRed) {
              // For RED, do not insert the codec again if it was already
              // inserted. audio/red for opus gets enabled by having RED before
              // the primary codec.
              const auto fmtp =
                  codec.params.find(cricket::kCodecParamNotInNameValueFormat);
              if (fmtp != codec.params.end()) {
                std::vector<absl::string_view> redundant_payloads =
                    rtc::split(fmtp->second, '/');
                if (!redundant_payloads.empty() &&
                    redundant_payloads[0] == id) {
                  if (!red_was_added) {
                    filtered_codecs.push_back(codec);
                    red_was_added = true;
                  }
                  break;
                }
              }
            }
          }
        }
      }
    }
  }

  return filtered_codecs;
}

// Compute the union of `codecs1` and `codecs2`.
std::vector<Codec> ComputeCodecsUnion(const std::vector<Codec>& codecs1,
                                      const std::vector<Codec>& codecs2) {
  std::vector<Codec> all_codecs;
  UsedPayloadTypes used_payload_types;
  for (const Codec& codec : codecs1) {
    Codec codec_mutable = codec;
    used_payload_types.FindAndSetIdUsed(&codec_mutable);
    all_codecs.push_back(codec_mutable);
  }

  // Use MergeCodecs to merge the second half of our list as it already checks
  // and fixes problems with duplicate payload types.
  MergeCodecs(codecs2, &all_codecs, &used_payload_types);

  return all_codecs;
}

// Adds all extensions from `reference_extensions` to `offered_extensions` that
// don't already exist in `offered_extensions` and ensures the IDs don't
// collide. If an extension is added, it's also added to
// `all_encountered_extensions`. Also when doing the addition a new ID is set
// for that extension. `offered_extensions` is for either audio or video while
// `all_encountered_extensions` is used for both audio and video. There could be
// overlap between audio extensions and video extensions.
void MergeRtpHdrExts(const RtpHeaderExtensions& reference_extensions,
                     bool enable_encrypted_rtp_header_extensions,
                     RtpHeaderExtensions* offered_extensions,
                     RtpHeaderExtensions* all_encountered_extensions,
                     UsedRtpHeaderExtensionIds* used_ids) {
  for (auto reference_extension : reference_extensions) {
    if (!webrtc::RtpExtension::FindHeaderExtensionByUriAndEncryption(
            *offered_extensions, reference_extension.uri,
            reference_extension.encrypt)) {
      if (reference_extension.encrypt &&
          !enable_encrypted_rtp_header_extensions) {
        // Negotiating of encrypted headers is deactivated.
        continue;
      }
      const webrtc::RtpExtension* existing =
          webrtc::RtpExtension::FindHeaderExtensionByUriAndEncryption(
              *all_encountered_extensions, reference_extension.uri,
              reference_extension.encrypt);
      if (existing) {
        // E.g. in the case where the same RTP header extension is used for
        // audio and video.
        offered_extensions->push_back(*existing);
      } else {
        used_ids->FindAndSetIdUsed(&reference_extension);
        all_encountered_extensions->push_back(reference_extension);
        offered_extensions->push_back(reference_extension);
      }
    }
  }
}

// Mostly identical to RtpExtension::FindHeaderExtensionByUri but discards any
// encrypted extensions that this implementation cannot encrypt.
const webrtc::RtpExtension* FindHeaderExtensionByUriDiscardUnsupported(
    const std::vector<webrtc::RtpExtension>& extensions,
    absl::string_view uri,
    webrtc::RtpExtension::Filter filter) {
  // Note: While it's technically possible to decrypt extensions that we don't
  // encrypt, the symmetric API of libsrtp does not allow us to supply
  // different IDs for encryption/decryption of header extensions depending on
  // whether the packet is inbound or outbound. Thereby, we are limited to
  // what we can send in encrypted form.
  if (!webrtc::RtpExtension::IsEncryptionSupported(uri)) {
    // If there's no encryption support and we only want encrypted extensions,
    // there's no point in continuing the search here.
    if (filter == webrtc::RtpExtension::kRequireEncryptedExtension) {
      return nullptr;
    }

    // Instruct to only return non-encrypted extensions
    filter = webrtc::RtpExtension::Filter::kDiscardEncryptedExtension;
  }

  return webrtc::RtpExtension::FindHeaderExtensionByUri(extensions, uri,
                                                        filter);
}

void NegotiateRtpHeaderExtensions(const RtpHeaderExtensions& local_extensions,
                                  const RtpHeaderExtensions& offered_extensions,
                                  webrtc::RtpExtension::Filter filter,
                                  RtpHeaderExtensions* negotiated_extensions) {
  bool frame_descriptor_in_local = false;
  bool dependency_descriptor_in_local = false;
  bool abs_capture_time_in_local = false;

  for (const webrtc::RtpExtension& ours : local_extensions) {
    if (ours.uri == webrtc::RtpExtension::kGenericFrameDescriptorUri00)
      frame_descriptor_in_local = true;
    else if (ours.uri == webrtc::RtpExtension::kDependencyDescriptorUri)
      dependency_descriptor_in_local = true;
    else if (ours.uri == webrtc::RtpExtension::kAbsoluteCaptureTimeUri)
      abs_capture_time_in_local = true;

    const webrtc::RtpExtension* theirs =
        FindHeaderExtensionByUriDiscardUnsupported(offered_extensions, ours.uri,
                                                   filter);
    if (theirs && theirs->encrypt == ours.encrypt) {
      // We respond with their RTP header extension id.
      negotiated_extensions->push_back(*theirs);
    }
  }

  // Frame descriptors support. If the extension is not present locally, but is
  // in the offer, we add it to the list.
  if (!dependency_descriptor_in_local) {
    const webrtc::RtpExtension* theirs =
        FindHeaderExtensionByUriDiscardUnsupported(
            offered_extensions, webrtc::RtpExtension::kDependencyDescriptorUri,
            filter);
    if (theirs) {
      negotiated_extensions->push_back(*theirs);
    }
  }
  if (!frame_descriptor_in_local) {
    const webrtc::RtpExtension* theirs =
        FindHeaderExtensionByUriDiscardUnsupported(
            offered_extensions,
            webrtc::RtpExtension::kGenericFrameDescriptorUri00, filter);
    if (theirs) {
      negotiated_extensions->push_back(*theirs);
    }
  }

  // Absolute capture time support. If the extension is not present locally, but
  // is in the offer, we add it to the list.
  if (!abs_capture_time_in_local) {
    const webrtc::RtpExtension* theirs =
        FindHeaderExtensionByUriDiscardUnsupported(
            offered_extensions, webrtc::RtpExtension::kAbsoluteCaptureTimeUri,
            filter);
    if (theirs) {
      negotiated_extensions->push_back(*theirs);
    }
  }
}

bool SetCodecsInAnswer(const MediaContentDescription* offer,
                       const std::vector<Codec>& local_codecs,
                       const MediaDescriptionOptions& media_description_options,
                       const MediaSessionOptions& session_options,
                       UniqueRandomIdGenerator* ssrc_generator,
                       StreamParamsVec* current_streams,
                       MediaContentDescription* answer,
                       const webrtc::FieldTrialsView& field_trials) {
  RTC_DCHECK(offer->type() == MEDIA_TYPE_AUDIO ||
             offer->type() == MEDIA_TYPE_VIDEO);
  answer->AddCodecs(local_codecs);
  answer->set_protocol(offer->protocol());
  if (!AddStreamParams(media_description_options.sender_options,
                       session_options.rtcp_cname, ssrc_generator,
                       current_streams, answer, field_trials)) {
    return false;  // Something went seriously wrong.
  }
  return true;
}

// Create a media content to be answered for the given `sender_options`
// according to the given session_options.rtcp_mux, session_options.streams,
// codecs, crypto, and current_streams.  If we don't currently have crypto (in
// current_cryptos) and it is enabled (in secure_policy), crypto is created
// (according to crypto_suites). The codecs, rtcp_mux, and crypto are all
// negotiated with the offer. If the negotiation fails, this method returns
// false.  The created content is added to the offer.
bool CreateMediaContentAnswer(
    const MediaContentDescription* offer,
    const MediaDescriptionOptions& media_description_options,
    const MediaSessionOptions& session_options,
    const RtpHeaderExtensions& local_rtp_extensions,
    UniqueRandomIdGenerator* ssrc_generator,
    bool enable_encrypted_rtp_header_extensions,
    StreamParamsVec* current_streams,
    bool bundle_enabled,
    MediaContentDescription* answer) {
  answer->set_extmap_allow_mixed_enum(offer->extmap_allow_mixed_enum());
  const webrtc::RtpExtension::Filter extensions_filter =
      enable_encrypted_rtp_header_extensions
          ? webrtc::RtpExtension::Filter::kPreferEncryptedExtension
          : webrtc::RtpExtension::Filter::kDiscardEncryptedExtension;

  // Filter local extensions by capabilities and direction.
  RtpHeaderExtensions local_rtp_extensions_to_reply_with;
  for (const auto& extension_with_id : local_rtp_extensions) {
    for (const auto& extension : media_description_options.header_extensions) {
      if (extension_with_id.uri == extension.uri &&
          extension_with_id.encrypt == extension.preferred_encrypt) {
        // TODO(crbug.com/1051821): Configure the extension direction from
        // the information in the media_description_options extension
        // capability. For now, do not include stopped extensions.
        // See also crbug.com/webrtc/7477 about the general lack of direction.
        if (extension.direction != RtpTransceiverDirection::kStopped) {
          local_rtp_extensions_to_reply_with.push_back(extension_with_id);
        }
      }
    }
  }
  RtpHeaderExtensions negotiated_rtp_extensions;
  NegotiateRtpHeaderExtensions(local_rtp_extensions_to_reply_with,
                               offer->rtp_header_extensions(),
                               extensions_filter, &negotiated_rtp_extensions);
  answer->set_rtp_header_extensions(negotiated_rtp_extensions);

  answer->set_rtcp_mux(session_options.rtcp_mux_enabled && offer->rtcp_mux());
  answer->set_rtcp_reduced_size(offer->rtcp_reduced_size());
  answer->set_remote_estimate(offer->remote_estimate());

  AddSimulcastToMediaDescription(media_description_options, answer);

  answer->set_direction(NegotiateRtpTransceiverDirection(
      offer->direction(), media_description_options.direction));

  return true;
}

bool IsMediaProtocolSupported(MediaType type,
                              const std::string& protocol,
                              bool secure_transport) {
  // Since not all applications serialize and deserialize the media protocol,
  // we will have to accept `protocol` to be empty.
  if (protocol.empty()) {
    return true;
  }

  if (type == MEDIA_TYPE_DATA) {
    // Check for SCTP
    if (secure_transport) {
      // Most likely scenarios first.
      return IsDtlsSctp(protocol);
    } else {
      return IsPlainSctp(protocol);
    }
  }

  // Allow for non-DTLS RTP protocol even when using DTLS because that's what
  // JSEP specifies.
  if (secure_transport) {
    // Most likely scenarios first.
    return IsDtlsRtp(protocol) || IsPlainRtp(protocol);
  } else {
    return IsPlainRtp(protocol);
  }
}

void SetMediaProtocol(bool secure_transport, MediaContentDescription* desc) {
  if (secure_transport)
    desc->set_protocol(kMediaProtocolDtlsSavpf);
  else
    desc->set_protocol(kMediaProtocolAvpf);
}

// Gets the TransportInfo of the given `content_name` from the
// `current_description`. If doesn't exist, returns a new one.
const TransportDescription* GetTransportDescription(
    const std::string& content_name,
    const SessionDescription* current_description) {
  const TransportDescription* desc = NULL;
  if (current_description) {
    const TransportInfo* info =
        current_description->GetTransportInfoByName(content_name);
    if (info) {
      desc = &info->description;
    }
  }
  return desc;
}

webrtc::RTCErrorOr<Codecs> GetNegotiatedCodecsForOffer(
    const MediaDescriptionOptions& media_description_options,
    const MediaSessionOptions& session_options,
    const ContentInfo* current_content,
    const std::vector<Codec>& codecs,
    const std::vector<Codec>& supported_codecs) {
  std::vector<Codec> filtered_codecs;
  if (!media_description_options.codec_preferences.empty()) {
    // Add the codecs from the current transceiver's codec preferences.
    // They override any existing codecs from previous negotiations.
    filtered_codecs = MatchCodecPreference(
        media_description_options.codec_preferences, codecs, supported_codecs);
  } else {
    // Add the codecs from current content if it exists and is not rejected nor
    // recycled.
    if (current_content && !current_content->rejected &&
        current_content->name == media_description_options.mid) {
      if (!IsMediaContentOfType(current_content,
                                media_description_options.type)) {
        // Can happen if the remote side re-uses a MID while recycling.
        LOG_AND_RETURN_ERROR(RTCErrorType::INTERNAL_ERROR,
                             "Media type for content with mid='" +
                                 current_content->name +
                                 "' does not match previous type.");
      }
      const MediaContentDescription* mcd = current_content->media_description();
      for (const Codec& codec : mcd->codecs()) {
        if (webrtc::FindMatchingCodec(mcd->codecs(), codecs, codec)) {
          filtered_codecs.push_back(codec);
        }
      }
    }
    // Add other supported codecs.
    for (const Codec& codec : supported_codecs) {
      std::optional<Codec> found_codec =
          webrtc::FindMatchingCodec(supported_codecs, codecs, codec);
      if (found_codec && !webrtc::FindMatchingCodec(supported_codecs,
                                                    filtered_codecs, codec)) {
        // Use the `found_codec` from `codecs` because it has the
        // correctly mapped payload type.
        // This is only done for video since we do not yet have rtx for audio.
        if (media_description_options.type == MEDIA_TYPE_VIDEO &&
            found_codec->GetResiliencyType() == Codec::ResiliencyType::kRtx) {
          // For RTX we might need to adjust the apt parameter if we got a
          // remote offer without RTX for a codec for which we support RTX.
          auto referenced_codec =
              GetAssociatedCodecForRtx(supported_codecs, codec);
          RTC_DCHECK(referenced_codec);

          // Find the codec we should be referencing and point to it.
          std::optional<Codec> changed_referenced_codec =
              webrtc::FindMatchingCodec(supported_codecs, filtered_codecs,
                                        *referenced_codec);
          if (changed_referenced_codec) {
            found_codec->SetParam(kCodecParamAssociatedPayloadType,
                                  changed_referenced_codec->id);
          }
        }
        filtered_codecs.push_back(*found_codec);
      }
    }
  }

  if (media_description_options.type == MEDIA_TYPE_AUDIO &&
      !session_options.vad_enabled) {
    // If application doesn't want CN codecs in offer.
    StripCNCodecs(&filtered_codecs);
  } else if (media_description_options.type == MEDIA_TYPE_VIDEO &&
             session_options.raw_packetization_for_video) {
    for (Codec& codec : filtered_codecs) {
      if (codec.IsMediaCodec()) {
        codec.packetization = kPacketizationParamRaw;
      }
    }
  }
  return filtered_codecs;
}

webrtc::RTCErrorOr<Codecs> GetNegotiatedCodecsForAnswer(
    const MediaDescriptionOptions& media_description_options,
    const MediaSessionOptions& session_options,
    const ContentInfo* current_content,
    const std::vector<Codec>& codecs,
    const std::vector<Codec>& supported_codecs) {
  std::vector<Codec> filtered_codecs;

  if (!media_description_options.codec_preferences.empty()) {
    filtered_codecs = MatchCodecPreference(
        media_description_options.codec_preferences, codecs, supported_codecs);
  } else {
    // Add the codecs from current content if it exists and is not rejected nor
    // recycled.
    if (current_content && !current_content->rejected &&
        current_content->name == media_description_options.mid) {
      if (!IsMediaContentOfType(current_content,
                                media_description_options.type)) {
        // Can happen if the remote side re-uses a MID while recycling.
        LOG_AND_RETURN_ERROR(RTCErrorType::INTERNAL_ERROR,
                             "Media type for content with mid='" +
                                 current_content->name +
                                 "' does not match previous type.");
      }
      const MediaContentDescription* mcd = current_content->media_description();
      for (const Codec& codec : mcd->codecs()) {
        if (webrtc::FindMatchingCodec(mcd->codecs(), codecs, codec)) {
          filtered_codecs.push_back(codec);
        }
      }
    }
    // Add other supported codecs.
    std::vector<Codec> other_codecs;
    for (const Codec& codec : supported_codecs) {
      if (webrtc::FindMatchingCodec(supported_codecs, codecs, codec) &&
          !webrtc::FindMatchingCodec(supported_codecs, filtered_codecs,
                                     codec)) {
        // We should use the local codec with local parameters and the codec id
        // would be correctly mapped in `NegotiateCodecs`.
        other_codecs.push_back(codec);
      }
    }

    // Use ComputeCodecsUnion to avoid having duplicate payload IDs.
    // This is a no-op for audio until RTX is added.
    filtered_codecs = ComputeCodecsUnion(filtered_codecs, other_codecs);
  }

  if (media_description_options.type == MEDIA_TYPE_AUDIO &&
      !session_options.vad_enabled) {
    // If application doesn't want CN codecs in offer.
    StripCNCodecs(&filtered_codecs);
  } else if (media_description_options.type == MEDIA_TYPE_VIDEO &&
             session_options.raw_packetization_for_video) {
    for (Codec& codec : filtered_codecs) {
      if (codec.IsMediaCodec()) {
        codec.packetization = kPacketizationParamRaw;
      }
    }
  }
  return filtered_codecs;
}

}  // namespace

void MediaDescriptionOptions::AddAudioSender(
    const std::string& track_id,
    const std::vector<std::string>& stream_ids) {
  RTC_DCHECK(type == MEDIA_TYPE_AUDIO);
  AddSenderInternal(track_id, stream_ids, {}, SimulcastLayerList(), 1);
}

void MediaDescriptionOptions::AddVideoSender(
    const std::string& track_id,
    const std::vector<std::string>& stream_ids,
    const std::vector<RidDescription>& rids,
    const SimulcastLayerList& simulcast_layers,
    int num_sim_layers) {
  RTC_DCHECK(type == MEDIA_TYPE_VIDEO);
  RTC_DCHECK(rids.empty() || num_sim_layers == 0)
      << "RIDs are the compliant way to indicate simulcast.";
  RTC_DCHECK(ValidateSimulcastLayers(rids, simulcast_layers));
  AddSenderInternal(track_id, stream_ids, rids, simulcast_layers,
                    num_sim_layers);
}

void MediaDescriptionOptions::AddSenderInternal(
    const std::string& track_id,
    const std::vector<std::string>& stream_ids,
    const std::vector<RidDescription>& rids,
    const SimulcastLayerList& simulcast_layers,
    int num_sim_layers) {
  // TODO(steveanton): Support any number of stream ids.
  RTC_CHECK(stream_ids.size() == 1U);
  SenderOptions options;
  options.track_id = track_id;
  options.stream_ids = stream_ids;
  options.simulcast_layers = simulcast_layers;
  options.rids = rids;
  options.num_sim_layers = num_sim_layers;
  sender_options.push_back(options);
}

bool MediaSessionOptions::HasMediaDescription(MediaType type) const {
  return absl::c_any_of(
      media_description_options,
      [type](const MediaDescriptionOptions& t) { return t.type == type; });
}

MediaSessionDescriptionFactory::MediaSessionDescriptionFactory(
    cricket::MediaEngineInterface* media_engine,
    bool rtx_enabled,
    rtc::UniqueRandomIdGenerator* ssrc_generator,
    const TransportDescriptionFactory* transport_desc_factory,
    webrtc::PayloadTypeSuggester* pt_suggester)
    : ssrc_generator_(ssrc_generator),
      transport_desc_factory_(transport_desc_factory),
      pt_suggester_(pt_suggester),
      payload_types_in_transport_trial_enabled_(
          transport_desc_factory_->trials().IsEnabled(
              "WebRTC-PayloadTypesInTransport")) {
  RTC_CHECK(transport_desc_factory_);
  if (media_engine) {
    audio_send_codecs_ = media_engine->voice().send_codecs();
    audio_recv_codecs_ = media_engine->voice().recv_codecs();
    video_send_codecs_ = media_engine->video().send_codecs(rtx_enabled);
    video_recv_codecs_ = media_engine->video().recv_codecs(rtx_enabled);
  }
  ComputeAudioCodecsIntersectionAndUnion();
  ComputeVideoCodecsIntersectionAndUnion();
}

const Codecs& MediaSessionDescriptionFactory::audio_sendrecv_codecs() const {
  return audio_sendrecv_codecs_;
}

const Codecs& MediaSessionDescriptionFactory::audio_send_codecs() const {
  return audio_send_codecs_;
}

const Codecs& MediaSessionDescriptionFactory::audio_recv_codecs() const {
  return audio_recv_codecs_;
}

void MediaSessionDescriptionFactory::set_audio_codecs(
    const Codecs& send_codecs,
    const Codecs& recv_codecs) {
  audio_send_codecs_ = send_codecs;
  audio_recv_codecs_ = recv_codecs;
  ComputeAudioCodecsIntersectionAndUnion();
}

const Codecs& MediaSessionDescriptionFactory::video_sendrecv_codecs() const {
  return video_sendrecv_codecs_;
}

const Codecs& MediaSessionDescriptionFactory::video_send_codecs() const {
  return video_send_codecs_;
}

const Codecs& MediaSessionDescriptionFactory::video_recv_codecs() const {
  return video_recv_codecs_;
}

void MediaSessionDescriptionFactory::set_video_codecs(
    const Codecs& send_codecs,
    const Codecs& recv_codecs) {
  video_send_codecs_ = send_codecs;
  video_recv_codecs_ = recv_codecs;
  ComputeVideoCodecsIntersectionAndUnion();
}

RtpHeaderExtensions
MediaSessionDescriptionFactory::filtered_rtp_header_extensions(
    RtpHeaderExtensions extensions) const {
  if (!is_unified_plan_) {
    // Remove extensions only supported with unified-plan.
    extensions.erase(
        std::remove_if(
            extensions.begin(), extensions.end(),
            [](const webrtc::RtpExtension& extension) {
              return extension.uri == webrtc::RtpExtension::kMidUri ||
                     extension.uri == webrtc::RtpExtension::kRidUri ||
                     extension.uri == webrtc::RtpExtension::kRepairedRidUri;
            }),
        extensions.end());
  }
  return extensions;
}

webrtc::RTCErrorOr<std::unique_ptr<SessionDescription>>
MediaSessionDescriptionFactory::CreateOfferOrError(
    const MediaSessionOptions& session_options,
    const SessionDescription* current_description) const {
  // Must have options for each existing section.
  if (current_description) {
    RTC_DCHECK_LE(current_description->contents().size(),
                  session_options.media_description_options.size());
  }

  IceCredentialsIterator ice_credentials(
      session_options.pooled_ice_credentials);

  std::vector<const ContentInfo*> current_active_contents;
  if (current_description) {
    current_active_contents =
        GetActiveContents(*current_description, session_options);
  }

  StreamParamsVec current_streams =
      GetCurrentStreamParams(current_active_contents);

  Codecs offer_audio_codecs;
  Codecs offer_video_codecs;
  GetCodecsForOffer(current_active_contents, &offer_audio_codecs,
                    &offer_video_codecs);

  AudioVideoRtpHeaderExtensions extensions_with_ids =
      GetOfferedRtpHeaderExtensionsWithIds(
          current_active_contents, session_options.offer_extmap_allow_mixed,
          session_options.media_description_options);

  auto offer = std::make_unique<SessionDescription>();

  // Iterate through the media description options, matching with existing media
  // descriptions in `current_description`.
  size_t msection_index = 0;
  for (const MediaDescriptionOptions& media_description_options :
       session_options.media_description_options) {
    const ContentInfo* current_content = nullptr;
    if (current_description &&
        msection_index < current_description->contents().size()) {
      current_content = ¤t_description->contents()[msection_index];
      // Media type must match unless this media section is being recycled.
    }
    RTCError error;
    switch (media_description_options.type) {
      case MEDIA_TYPE_AUDIO:
      case MEDIA_TYPE_VIDEO:
        error = AddRtpContentForOffer(
            media_description_options, session_options, current_content,
            current_description,
            media_description_options.type == MEDIA_TYPE_AUDIO
                ? extensions_with_ids.audio
                : extensions_with_ids.video,
            media_description_options.type == MEDIA_TYPE_AUDIO
                ? offer_audio_codecs
                : offer_video_codecs,
            ¤t_streams, offer.get(), &ice_credentials);
        break;
      case MEDIA_TYPE_DATA:
        error = AddDataContentForOffer(media_description_options,
                                       session_options, current_content,
                                       current_description, ¤t_streams,
                                       offer.get(), &ice_credentials);
        break;
      case MEDIA_TYPE_UNSUPPORTED:
        error = AddUnsupportedContentForOffer(
            media_description_options, session_options, current_content,
            current_description, offer.get(), &ice_credentials);
        break;
      default:
        RTC_DCHECK_NOTREACHED();
    }
    if (!error.ok()) {
      return error;
    }
    ++msection_index;
  }

  // Bundle the contents together, if we've been asked to do so, and update any
  // parameters that need to be tweaked for BUNDLE.
  if (session_options.bundle_enabled) {
    ContentGroup offer_bundle(GROUP_TYPE_BUNDLE);
    for (const ContentInfo& content : offer->contents()) {
      if (content.rejected) {
        continue;
      }
      // TODO(deadbeef): There are conditions that make bundling two media
      // descriptions together illegal. For example, they use the same payload
      // type to represent different codecs, or same IDs for different header
      // extensions. We need to detect this and not try to bundle those media
      // descriptions together.
      offer_bundle.AddContentName(content.name);
    }
    if (!offer_bundle.content_names().empty()) {
      offer->AddGroup(offer_bundle);
      if (!UpdateTransportInfoForBundle(offer_bundle, offer.get())) {
        LOG_AND_RETURN_ERROR(
            RTCErrorType::INTERNAL_ERROR,
            "CreateOffer failed to UpdateTransportInfoForBundle");
      }
    }
  }

  // The following determines how to signal MSIDs to ensure compatibility with
  // older endpoints (in particular, older Plan B endpoints).
  if (is_unified_plan_) {
    // Be conservative and signal using both a=msid and a=ssrc lines. Unified
    // Plan answerers will look at a=msid and Plan B answerers will look at the
    // a=ssrc MSID line.
    offer->set_msid_signaling(cricket::kMsidSignalingSemantic |
                              cricket::kMsidSignalingMediaSection |
                              cricket::kMsidSignalingSsrcAttribute);
  } else {
    // Plan B always signals MSID using a=ssrc lines.
    offer->set_msid_signaling(cricket::kMsidSignalingSemantic |
                              cricket::kMsidSignalingSsrcAttribute);
  }

  offer->set_extmap_allow_mixed(session_options.offer_extmap_allow_mixed);

  return offer;
}

webrtc::RTCErrorOr<std::unique_ptr<SessionDescription>>
MediaSessionDescriptionFactory::CreateAnswerOrError(
    const SessionDescription* offer,
    const MediaSessionOptions& session_options,
    const SessionDescription* current_description) const {
  if (!offer) {
    LOG_AND_RETURN_ERROR(RTCErrorType::INTERNAL_ERROR, "Called without offer.");
  }

  // Must have options for exactly as many sections as in the offer.
  RTC_DCHECK_EQ(offer->contents().size(),
                session_options.media_description_options.size());

  IceCredentialsIterator ice_credentials(
      session_options.pooled_ice_credentials);

  std::vector<const ContentInfo*> current_active_contents;
  if (current_description) {
    current_active_contents =
        GetActiveContents(*current_description, session_options);
  }

  StreamParamsVec current_streams =
      GetCurrentStreamParams(current_active_contents);

  // Get list of all possible codecs that respects existing payload type
  // mappings and uses a single payload type space.
  //
  // Note that these lists may be further filtered for each m= section; this
  // step is done just to establish the payload type mappings shared by all
  // sections.
  Codecs answer_audio_codecs;
  Codecs answer_video_codecs;
  GetCodecsForAnswer(current_active_contents, *offer, &answer_audio_codecs,
                     &answer_video_codecs);

  auto answer = std::make_unique<SessionDescription>();

  // If the offer supports BUNDLE, and we want to use it too, create a BUNDLE
  // group in the answer with the appropriate content names.
  std::vector<const ContentGroup*> offer_bundles =
      offer->GetGroupsByName(GROUP_TYPE_BUNDLE);
  // There are as many answer BUNDLE groups as offer BUNDLE groups (even if
  // rejected, we respond with an empty group). `offer_bundles`,
  // `answer_bundles` and `bundle_transports` share the same size and indices.
  std::vector<ContentGroup> answer_bundles;
  std::vector<std::unique_ptr<TransportInfo>> bundle_transports;
  answer_bundles.reserve(offer_bundles.size());
  bundle_transports.reserve(offer_bundles.size());
  for (size_t i = 0; i < offer_bundles.size(); ++i) {
    answer_bundles.emplace_back(GROUP_TYPE_BUNDLE);
    bundle_transports.emplace_back(nullptr);
  }

  answer->set_extmap_allow_mixed(offer->extmap_allow_mixed());

  // Iterate through the media description options, matching with existing
  // media descriptions in `current_description`.
  size_t msection_index = 0;
  for (const MediaDescriptionOptions& media_description_options :
       session_options.media_description_options) {
    const ContentInfo* offer_content = &offer->contents()[msection_index];
    // Media types and MIDs must match between the remote offer and the
    // MediaDescriptionOptions.
    RTC_DCHECK(
        IsMediaContentOfType(offer_content, media_description_options.type));
    RTC_DCHECK(media_description_options.mid == offer_content->name);
    // Get the index of the BUNDLE group that this MID belongs to, if any.
    std::optional<size_t> bundle_index;
    for (size_t i = 0; i < offer_bundles.size(); ++i) {
      if (offer_bundles[i]->HasContentName(media_description_options.mid)) {
        bundle_index = i;
        break;
      }
    }
    TransportInfo* bundle_transport =
        bundle_index.has_value() ? bundle_transports[bundle_index.value()].get()
                                 : nullptr;

    const ContentInfo* current_content = nullptr;
    if (current_description &&
        msection_index < current_description->contents().size()) {
      current_content = ¤t_description->contents()[msection_index];
    }
    RtpHeaderExtensions header_extensions = RtpHeaderExtensionsFromCapabilities(
        UnstoppedRtpHeaderExtensionCapabilities(
            media_description_options.header_extensions));
    RTCError error;
    switch (media_description_options.type) {
      case MEDIA_TYPE_AUDIO:
      case MEDIA_TYPE_VIDEO:
        error = AddRtpContentForAnswer(
            media_description_options, session_options, offer_content, offer,
            current_content, current_description, bundle_transport,
            media_description_options.type == MEDIA_TYPE_AUDIO
                ? answer_audio_codecs
                : answer_video_codecs,
            header_extensions, ¤t_streams, answer.get(),
            &ice_credentials);
        break;
      case MEDIA_TYPE_DATA:
        error = AddDataContentForAnswer(
            media_description_options, session_options, offer_content, offer,
            current_content, current_description, bundle_transport,
            ¤t_streams, answer.get(), &ice_credentials);
        break;
      case MEDIA_TYPE_UNSUPPORTED:
        error = AddUnsupportedContentForAnswer(
            media_description_options, session_options, offer_content, offer,
            current_content, current_description, bundle_transport,
            answer.get(), &ice_credentials);
        break;
      default:
        RTC_DCHECK_NOTREACHED();
    }
    if (!error.ok()) {
      return error;
    }
    ++msection_index;
    // See if we can add the newly generated m= section to the BUNDLE group in
    // the answer.
    ContentInfo& added = answer->contents().back();
    if (!added.rejected && session_options.bundle_enabled &&
        bundle_index.has_value()) {
      // The `bundle_index` is for `media_description_options.mid`.
      RTC_DCHECK_EQ(media_description_options.mid, added.name);
      answer_bundles[bundle_index.value()].AddContentName(added.name);
      bundle_transports[bundle_index.value()].reset(
          new TransportInfo(*answer->GetTransportInfoByName(added.name)));
    }
  }

  // If BUNDLE group(s) were offered, put the same number of BUNDLE groups in
  // the answer even if they're empty. RFC5888 says:
  //
  //   A SIP entity that receives an offer that contains an "a=group" line
  //   with semantics that are understood MUST return an answer that
  //   contains an "a=group" line with the same semantics.
  if (!offer_bundles.empty()) {
    for (const ContentGroup& answer_bundle : answer_bundles) {
      answer->AddGroup(answer_bundle);

      if (answer_bundle.FirstContentName()) {
        // Share the same ICE credentials and crypto params across all contents,
        // as BUNDLE requires.
        if (!UpdateTransportInfoForBundle(answer_bundle, answer.get())) {
          LOG_AND_RETURN_ERROR(
              RTCErrorType::INTERNAL_ERROR,
              "CreateAnswer failed to UpdateTransportInfoForBundle.");
        }
      }
    }
  }

  // The following determines how to signal MSIDs to ensure compatibility with
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