webrtc codec

1、视频

std::unique_ptr<VideoEncoder> InternalEncoderFactory::CreateVideoEncoder(
    const SdpVideoFormat& format) {
  if (absl::EqualsIgnoreCase(format.name, cricket::kVp8CodecName))
    return VP8Encoder::Create();
  if (absl::EqualsIgnoreCase(format.name, cricket::kVp9CodecName))
    return VP9Encoder::Create(cricket::VideoCodec(format));
  if (absl::EqualsIgnoreCase(format.name, cricket::kH264CodecName))
    return H264Encoder::Create(cricket::VideoCodec(format));
  RTC_LOG(LS_ERROR) << "Trying to created encoder of unsupported format "
                    << format.name;
  return nullptr;
}

　从上到下的优先级的形式设置

2 音频

WebRtcVoiceMediaChannel::SetRecvCodecs

WebRtcVoiceMediaChannel::SetSendCodecs

 for (const AudioCodec& voice_codec : codecs) {
    if (!(IsCodec(voice_codec, kCnCodecName) ||
          IsCodec(voice_codec, kDtmfCodecName) ||
          IsCodec(voice_codec, kRedCodecName))) {
      webrtc::SdpAudioFormat format(voice_codec.name, voice_codec.clockrate,
                                    voice_codec.channels, voice_codec.params);

      voice_codec_info = engine()->encoder_factory_->QueryAudioEncoder(format);
      if (!voice_codec_info) {
        RTC_LOG(LS_WARNING) << "Unknown codec " << ToString(voice_codec);
        continue;
      }

　　这个里边从codecs的列表里从头到尾的优先级找到当前使用的codec。

而这个codecs的列表数据，是音频引擎在启动的时候，获取到的，代码如下：

void WebRtcVoiceEngine::Init() {
  RTC_DCHECK(worker_thread_checker_.IsCurrent());
  RTC_LOG(LS_INFO) << "WebRtcVoiceEngine::Init";

  // TaskQueue expects to be created/destroyed on the same thread.
  low_priority_worker_queue_.reset(
      new rtc::TaskQueue(task_queue_factory_->CreateTaskQueue(
          "rtc-low-prio", webrtc::TaskQueueFactory::Priority::LOW)));

  // Load our audio codec lists.
  RTC_LOG(LS_VERBOSE) << "Supported send codecs in order of preference:";
  send_codecs_ = CollectCodecs(encoder_factory_->GetSupportedEncoders());
  for (const AudioCodec& codec : send_codecs_) {
    RTC_LOG(LS_VERBOSE) << ToString(codec);
  }

  RTC_LOG(LS_VERBOSE) << "Supported recv codecs in order of preference:";
  recv_codecs_ = CollectCodecs(decoder_factory_->GetSupportedDecoders());
  for (const AudioCodec& codec : recv_codecs_) {
    RTC_LOG(LS_VERBOSE) << ToString(codec);
  }

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