text: /*
   *  Copyright (c) 2017 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 "api/audio_codecs/opus/audio_decoder_opus.h"
  
  #include <memory>
  #include <utility>
  #include <vector>
  
  #include "absl/memory/memory.h"
  #include "absl/strings/match.h"
  #include "modules/audio_coding/codecs/opus/audio_decoder_opus.h"
  
  namespace webrtc {
  
  bool AudioDecoderOpus::Config::IsOk() const {
    if (sample_rate_hz != 16000 && sample_rate_hz != 48000) {
      // Unsupported sample rate. (libopus supports a few other rates as
      // well; we can add support for them when needed.)
      return false;
    }
    if (num_channels != 1 && num_channels != 2) {
      return false;
    }
    return true;
  }
  
  absl::optional<AudioDecoderOpus::Config> AudioDecoderOpus::SdpToConfig(
      const SdpAudioFormat& format) {
    const auto num_channels = [&]() -> absl::optional<int> {
      auto stereo = format.parameters.find("stereo");
      if (stereo != format.parameters.end()) {
        if (stereo->second == "0") {
          return 1;
        } else if (stereo->second == "1") {
          return 2;
        } else {
          return absl::nullopt;  // Bad stereo parameter.
        }
      }
      return 1;  // Default to mono.
    }();
    if (absl::EqualsIgnoreCase(format.name, "opus") &&
        format.clockrate_hz == 48000 && format.num_channels == 2 &&
        num_channels) {
      Config config;
      config.num_channels = *num_channels;
      RTC_DCHECK(config.IsOk());
      return config;
    } else {
      return absl::nullopt;
    }
  }
  
  void AudioDecoderOpus::AppendSupportedDecoders(
      std::vector<AudioCodecSpec>* specs) {
    AudioCodecInfo opus_info{48000, 1, 64000, 6000, 510000};
    opus_info.allow_comfort_noise = false;
    opus_info.supports_network_adaption = true;
    SdpAudioFormat opus_format(
        {"opus", 48000, 2, {{"minptime", "10"}, {"useinbandfec", "1"}}});
    specs->push_back({std::move(opus_format), opus_info});
  }
  
  std::unique_ptr<AudioDecoder> AudioDecoderOpus::MakeAudioDecoder(
      Config config,
      absl::optional<AudioCodecPairId> /*codec_pair_id*/) {
    RTC_DCHECK(config.IsOk());
    return absl::make_unique<AudioDecoderOpusImpl>(config.num_channels,
                                                   config.sample_rate_hz);
  }
  
  }  // namespace webrtc
  