webrtc音视频

std::vector
WebRtcVideoChannel::SelectSendVideoCodecs(
    const std::vector& remote_mapped_codecs) const {
  std::vector sdp_formats =
      encoder_factory_ ? encoder_factory_->GetImplementations()
                       : std::vector();

  // The returned vector holds the VideoCodecSettings in term of preference.
  // They are orderd by receive codec preference first and local implementation
  // preference second.
  std::vector encoders;
  for (const VideoCodecSettings& remote_codec : remote_mapped_codecs) {//遍历远端的codec
    for (auto format_it = sdp_formats.begin();
         format_it != sdp_formats.end();) {//遍历本地的codec
      // For H264, we will limit the encode level to the remote offered level
      // regardless if level asymmetry is allowed or not. This is strictly not
      // following the spec in https://tools.ietf.org/html/rfc6184#section-8.2.2
      // since we should limit the encode level to the lower of local and remote
      // level when level asymmetry is not allowed.
      if (IsSameCodec(format_it->name, format_it->parameters,
                      remote_codec.codec.name, remote_codec.codec.params)) {//本地与远端的codec是否相同
        encoders.push_back(remote_codec);

        // To allow the VideoEncoderFactory to keep information about which
        // implementation to instantitate when CreateEncoder is called the two
        // parmeter sets are merged.
        encoders.back().codec.params.insert(format_it->parameters.begin(),
                                            format_it->parameters.end());

        format_it = sdp_formats.erase(format_it);
      } else {
        ++format_it;
      }
    }
  }

  return encoders;//本地与远端都支持的codecs
}