webrtc-m79-音频相关 DecoderDatabase 中 decoders_ 的设置

1 代码

void AudioReceiveStream::ConfigureStream(AudioReceiveStream* stream,
                                         const Config& new_config,
                                         bool first_time) {
  RTC_LOG(LS_INFO) << "AudioReceiveStream::ConfigureStream: "
                   << new_config.ToString();
  RTC_DCHECK(stream);
  const auto& channel_receive = stream->channel_receive_;
  const auto& old_config = stream->config_;

  // Configuration parameters which cannot be changed.
  RTC_DCHECK(first_time ||
             old_config.rtp.remote_ssrc == new_config.rtp.remote_ssrc);
  RTC_DCHECK(first_time ||
             old_config.rtcp_send_transport == new_config.rtcp_send_transport);
  // Decoder factory cannot be changed because it is configured at
  // voe::Channel construction time.
  RTC_DCHECK(first_time ||
             old_config.decoder_factory == new_config.decoder_factory);

  if (!first_time) {
    // SSRC can't be changed mid-stream.
    RTC_DCHECK_EQ(old_config.rtp.local_ssrc, new_config.rtp.local_ssrc);
    RTC_DCHECK_EQ(old_config.rtp.remote_ssrc, new_config.rtp.remote_ssrc);
  }

  // TODO(solenberg): Config NACK history window (which is a packet count),
  // using the actual packet size for the configured codec.
  if (first_time || old_config.rtp.nack.rtp_history_ms !=
                        new_config.rtp.nack.rtp_history_ms) {
    channel_receive->SetNACKStatus(new_config.rtp.nack.rtp_history_ms != 0,
                                   new_config.rtp.nack.rtp_history_ms / 20);
  }
  if (first_time || old_config.decoder_map != new_config.decoder_map) {
    channel_receive->SetReceiveCodecs(new_config.decoder_map); //ChannelReceive::SetReceiveCodecs 
  }

  stream->config_ = new_config;
}


void ChannelReceive::SetReceiveCodecs(
    const std::map& codecs) {
  RTC_DCHECK(worker_thread_checker_.IsCurrent());
  for (const auto& kv : codecs) {
    RTC_DCHECK_GE(kv.second.clockrate_hz, 1000);
    payload_type_frequencies_[kv.first] = kv.second.clockrate_hz;
  }
  acm_receiver_.SetCodecs(codecs); // 注意这里
}

void AcmReceiver::SetCodecs(const std::map& codecs) {
  neteq_->SetCodecs(codecs);//注意这里
}

void NetEqImpl::SetCodecs(const std::map& codecs) {
  rtc::CritScope lock(&crit_sect_);
  const std::vector changed_payload_types =
      decoder_database_->SetCodecs(codecs); //注意这里
  for (const int pt : changed_payload_types) {
    packet_buffer_->DiscardPacketsWithPayloadType(pt, stats_.get());
  }
}

std::vector DecoderDatabase::SetCodecs(
    const std::map& codecs) {
  // First collect all payload types that we'll remove or reassign, then remove
  // them from the database.
  std::vector changed_payload_types;
  for (const std::pair kv : decoders_) {
    auto i = codecs.find(kv.first);
    if (i == codecs.end() || i->second != kv.second.GetFormat()) {
      changed_payload_types.push_back(kv.first);
    }
  }
  for (int pl_type : changed_payload_types) {
    Remove(pl_type);
  }

  // Enter the new and changed payload type mappings into the database.
  for (const auto& kv : codecs) {
    const int& rtp_payload_type = kv.first;
    const SdpAudioFormat& audio_format = kv.second;
    RTC_DCHECK_GE(rtp_payload_type, 0);
    RTC_DCHECK_LE(rtp_payload_type, 0x7f);
    if (decoders_.count(rtp_payload_type) == 0) {
      decoders_.insert(std::make_pair( //注意这里
          rtp_payload_type,
          DecoderInfo(audio_format, codec_pair_id_, decoder_factory_.get())));// decoder_factory 就是 CreateBuiltinAudioDecoderFactory() 的返回值
    } else {
      // The mapping for this payload type hasn't changed.
    }
  }

  return changed_payload_types;
}


DecoderDatabase::DecoderInfo::DecoderInfo(
    const SdpAudioFormat& audio_format,
    absl::optional codec_pair_id,
    AudioDecoderFactory* factory)
    : DecoderInfo(audio_format, codec_pair_id, factory, audio_format.name) {}
    
    
DecoderDatabase::DecoderInfo::DecoderInfo(
    const SdpAudioFormat& audio_format,
    absl::optional codec_pair_id,
    AudioDecoderFactory* factory, //注意这里
    const std::string& codec_name)
    : name_(codec_name),
      audio_format_(audio_format),
      codec_pair_id_(codec_pair_id),
      factory_(factory), //注意这里
      cng_decoder_(CngDecoder::Create(audio_format)), //注意这里
      subtype_(SubtypeFromFormat(audio_format)) {}