AudioOptions

01、回音降噪 echo_cancellation

02、自动增益控制 auto_gain_control

03、噪声抑制 noise_suppression

04、 高通滤波器 highpass_filter

05、立体声交换 stereo_swapping

06、NetEq容量 audio_jitter_buffer_max_packets

07、NetEq快速模式 audio_jitter_buffer_fast_accelerate

08、jitter buffer最小延迟 audio_jitter_buffer_min_delay_ms

09、itter buffer是否适应延迟重传 audio_jitter_buffer_enable_rtx_handling

10、键盘检测 typing_detection

11、残留回声检测 residual_echo_detector

12、音频网络适配器 audio_network_adaptor_config

// 设置音频参数
bool WebRtcVoiceEngine::ApplyOptions(const AudioOptions& options_in) {
  RTC_DCHECK_RUN_ON(&worker_thread_checker_);
  RTC_LOG(LS_INFO) << "WebRtcVoiceEngine::ApplyOptions: "
                   << options_in.ToString();
  AudioOptions options = options_in;  // 选项在下面进行了修改
 
  // 设置和调整回声消除器选项。不使用硬件 AEC 时，默认使用桌面 AEC。
  bool use_mobile_software_aec = false;
 
#if defined(WEBRTC_IOS)
  if (options.ios_force_software_aec_HACK &&
      *options.ios_force_software_aec_HACK) {
    // 在ios上强制软件回声消除
    options.echo_cancellation = true;
    RTC_LOG(LS_WARNING)
        << "Force software AEC on iOS. May conflict with platform AEC.";
  } else {
    // 默认使用VPIO内置的回声消除
    options.echo_cancellation = false;
    RTC_LOG(LS_INFO) << "Always disable AEC on iOS. Use built-in instead.";
  }
#elif defined(WEBRTC_ANDROID)
  use_mobile_software_aec = true;
#endif
 
// Android 的噪声抑制选项
#if defined(WEBRTC_ANDROID)
  options.typing_detection = false;
  options.experimental_ns = false;
#endif
 
// 设置和调整增益控制选项.
#if defined(WEBRTC_IOS)
  // iOS平台使用VIPIO内置的降噪。
  options.auto_gain_control = false;
  options.experimental_agc = false;
  RTC_LOG(LS_INFO) << "Always disable AGC on iOS. Use built-in instead.";
#elif defined(WEBRTC_ANDROID)
  // Android平台关闭试验性AGC.
  options.experimental_agc = false;
#endif
 
#if defined(WEBRTC_IOS) || defined(WEBRTC_ANDROID)
  // 移动端(ios android)
  // 如果设置了"WebRTC-Audio-MinimizeResamplingOnMobile"则关闭AGC。
  // 然后如果开启降噪且未开启回声消除则关闭高通滤波器。。
  // (https://bugs.chromium.org/p/webrtc/issues/detail?id=6181).
  if (minimized_remsampling_on_mobile_trial_enabled_) {
    options.auto_gain_control = false;
    RTC_LOG(LS_INFO) << "Disable AGC according to field trial.";
    if (!(options.noise_suppression.value_or(false) ||
          options.echo_cancellation.value_or(false))) {
      // If possible, turn off the high-pass filter.
      RTC_LOG(LS_INFO)
          << "Disable high-pass filter in response to field trial.";
      options.highpass_filter = false;
    }
  }
#endif
 
  if (options.echo_cancellation) {
    // 目前只有android支持内置aec
    // 如果支持内置aec而且开启回声消除echo_cancellation和未开启use_delay_agnostic_aec
    // 且内置EnableBuiltInAEC时关闭软件回声消除从而使用平台内置回声消除。
    const bool built_in_aec = adm()->BuiltInAECIsAvailable();
    // 除了Android平台为true，其他平台默认为false
    if (built_in_aec) {
      // 此设备上存在内置 EC。 根据 echo_cancellation 音频选项启用/禁用它
      const bool enable_built_in_aec = *options.echo_cancellation;
      if (adm()->EnableBuiltInAEC(enable_built_in_aec) == 0 &&
          enable_built_in_aec) {
        // 如果启用内置 EC，则禁用内部软件 EC，即将软件 EC 替换为内置 EC
        options.echo_cancellation = false;
        RTC_LOG(LS_INFO)
            << "Disabling EC since built-in EC will be used instead";
      }
    }
  }
  // 判断是否支持平台内置agc,如果支持则关闭软件agc
  if (options.auto_gain_control) {
    bool built_in_agc_avaliable = adm()->BuiltInAGCIsAvailable();
    if (built_in_agc_avaliable) {
      if (adm()->EnableBuiltInAGC(*options.auto_gain_control) == 0 &&
          *options.auto_gain_control) {
        // 如果启用了内置 AGC，则禁用内部软件 AGC，即将软件 AGC 替换为内置 AGC
        options.auto_gain_control = false;
        RTC_LOG(LS_INFO)
            << "Disabling AGC since built-in AGC will be used instead";
      }
    }
  }
  // 如果支持平台内置降噪则关闭软件降噪
  if (options.noise_suppression) {
    if (adm()->BuiltInNSIsAvailable()) {
      bool builtin_ns = *options.noise_suppression;
      if (adm()->EnableBuiltInNS(builtin_ns) == 0 && builtin_ns) {
        // 如果启用了内置 NS，则禁用内部软件 NS
        // 即用内置 NS 替换软件 NS
        options.noise_suppression = false;
        RTC_LOG(LS_INFO)
            << "Disabling NS since built-in NS will be used instead";
      }
    }
  }
  // 立体声通道交换
  if (options.stereo_swapping) {
    RTC_LOG(LS_INFO) << "Stereo swapping enabled? " << *options.stereo_swapping;
    audio_state()->SetStereoChannelSwapping(*options.stereo_swapping);
  }
  // jitter buffer最大包数设置
  if (options.audio_jitter_buffer_max_packets) {
    RTC_LOG(LS_INFO) << "NetEq capacity is "
                     << *options.audio_jitter_buffer_max_packets;
    audio_jitter_buffer_max_packets_ =
        std::max(20, *options.audio_jitter_buffer_max_packets);
  }
  // jitter buffer加速设置
  if (options.audio_jitter_buffer_fast_accelerate) {
    RTC_LOG(LS_INFO) << "NetEq fast mode? "
                     << *options.audio_jitter_buffer_fast_accelerate;
    audio_jitter_buffer_fast_accelerate_ =
        *options.audio_jitter_buffer_fast_accelerate;
  }
  // jitter buffer最小延迟（毫秒）
  if (options.audio_jitter_buffer_min_delay_ms) {
    RTC_LOG(LS_INFO) << "NetEq minimum delay is "
                     << *options.audio_jitter_buffer_min_delay_ms;
    audio_jitter_buffer_min_delay_ms_ =
        *options.audio_jitter_buffer_min_delay_ms;
  }
  if (options.audio_jitter_buffer_enable_rtx_handling) {
    RTC_LOG(LS_INFO) << "NetEq handle reordered packets? "
                     << *options.audio_jitter_buffer_enable_rtx_handling;
    audio_jitter_buffer_enable_rtx_handling_ =
        *options.audio_jitter_buffer_enable_rtx_handling;
  }
 
  webrtc::AudioProcessing* ap = apm();
  if (!ap) {
    RTC_LOG(LS_INFO)
        << "No audio processing module present. No software-provided effects "
           "(AEC, NS, AGC, ...) are activated";
    return true;
  }
 
  if (options.experimental_ns) {
    experimental_ns_ = options.experimental_ns;
  }
 
  webrtc::AudioProcessing::Config apm_config = ap->GetConfig();
 
#if !(defined(WEBRTC_ANDROID) || defined(WEBRTC_IOS))
  if (experimental_ns_.has_value()) {
    apm_config.transient_suppression.enabled = experimental_ns_.value();
  }
#endif
 
  if (options.echo_cancellation) {
    apm_config.echo_canceller.enabled = *options.echo_cancellation;
    apm_config.echo_canceller.mobile_mode = use_mobile_software_aec;
  }
 
  if (options.auto_gain_control) {
    const bool enabled = *options.auto_gain_control;
    apm_config.gain_controller1.enabled = enabled;
#if defined(WEBRTC_IOS) || defined(WEBRTC_ANDROID)
    apm_config.gain_controller1.mode =
        apm_config.gain_controller1.kFixedDigital;
#else
    apm_config.gain_controller1.mode =
        apm_config.gain_controller1.kAdaptiveAnalog;
#endif
  }
  if (options.tx_agc_target_dbov) {
    apm_config.gain_controller1.target_level_dbfs = *options.tx_agc_target_dbov;
  }
  if (options.tx_agc_digital_compression_gain) {
    apm_config.gain_controller1.compression_gain_db =
        *options.tx_agc_digital_compression_gain;
  }
  if (options.tx_agc_limiter) {
    apm_config.gain_controller1.enable_limiter = *options.tx_agc_limiter;
  }
 
  if (options.highpass_filter) {
    apm_config.high_pass_filter.enabled = *options.highpass_filter;
  }
  // 残留回声检测
  if (options.residual_echo_detector) {
    apm_config.residual_echo_detector.enabled = *options.residual_echo_detector;
  }
 
  if (options.noise_suppression) {
    const bool enabled = *options.noise_suppression;
    apm_config.noise_suppression.enabled = enabled;
    apm_config.noise_suppression.level =
        webrtc::AudioProcessing::Config::NoiseSuppression::Level::kHigh;
    RTC_LOG(LS_INFO) << "NS set to " << enabled;
  }
  // 键盘声音检测
  if (options.typing_detection) {
    RTC_LOG(LS_INFO) << "Typing detection is enabled? "
                     << *options.typing_detection;
    apm_config.voice_detection.enabled = *options.typing_detection;
  }
 
  ap->ApplyConfig(apm_config);
  return true;
}