再论COM组件

重要的Activate方法

Activate方法

Activate支持的接口

源码分析

h:\webrtc-20210315\webrtc-20210315\webrtc\webrtc-checkout\src\media\engine\webrtc_voice_engine.cc

WebRtcVoiceEngine::Init

void WebRtcVoiceEngine::Init() {
***
  RTC_CHECK(adm());
  webrtc::adm_helpers::Init(adm());
***
}

这时候进入到
H:\webrtc-20210315\webrtc-20210315\webrtc\webrtc-checkout\src\media\engine\adm_helpers.cc
void Init(AudioDeviceModule* adm) 方法

webrtc::adm_helpers::Init

void Init(AudioDeviceModule* adm) {
  RTC_DCHECK(adm);
  RTC_CHECK_EQ(0, adm->Init()) << "Failed to initialize the ADM.";
  // Playout device.
  {
    if (adm->SetPlayoutDevice(AUDIO_DEVICE_ID) != 0) {
      RTC_LOG(LS_ERROR) << "Unable to set playout device.";
      return;
    }
    if (adm->InitSpeaker() != 0) {
      RTC_LOG(LS_ERROR) << "Unable to access speaker.";
    }
    // Set number of channels
    bool available = false;
    if (adm->StereoPlayoutIsAvailable(&available) != 0) {
      RTC_LOG(LS_ERROR) << "Failed to query stereo playout.";
    }
    if (adm->SetStereoPlayout(available) != 0) {
      RTC_LOG(LS_ERROR) << "Failed to set stereo playout mode.";
    }
  }
  // Recording device.
  {
    if (adm->SetRecordingDevice(AUDIO_DEVICE_ID) != 0) {
      RTC_LOG(LS_ERROR) << "Unable to set recording device.";
      return;
    }
    if (adm->InitMicrophone() != 0) {
      RTC_LOG(LS_ERROR) << "Unable to access microphone.";
    }
    // Set number of channels
    bool available = false;
    if (adm->StereoRecordingIsAvailable(&available) != 0) {
      RTC_LOG(LS_ERROR) << "Failed to query stereo recording.";
    }
    if (adm->SetStereoRecording(available) != 0) {
      RTC_LOG(LS_ERROR) << "Failed to set stereo recording mode.";
    }
  }
}

重点是adm->Init()

AudioDeviceModuleImpl::Init

int32_t AudioDeviceModuleImpl::Init() {
  RTC_LOG(INFO) << __FUNCTION__;
  if (initialized_)
    return 0;
  RTC_CHECK(audio_device_);
  AudioDeviceGeneric::InitStatus status = audio_device_->Init();
  RTC_HISTOGRAM_ENUMERATION(
      "WebRTC.Audio.InitializationResult", static_cast<int>(status),
      static_cast<int>(AudioDeviceGeneric::InitStatus::NUM_STATUSES));
  if (status != AudioDeviceGeneric::InitStatus::OK) {
    RTC_LOG(LS_ERROR) << "Audio device initialization failed.";
    return -1;
  }
  initialized_ = true;
  return 0;
}

重点是音频设备初始化 AudioDeviceGeneric::InitStatus status = audiodevice->Init();

AudioDeviceGeneric::InitStatus AudioDeviceWindowsCore::Init()

AudioDeviceGeneric::InitStatus AudioDeviceWindowsCore::Init() {
  MutexLock lock(&mutex_);
  if (_initialized) {
    return InitStatus::OK;
  }
  // Enumerate all audio rendering and capturing endpoint devices.
  // Note that, some of these will not be able to select by the user.
  // The complete collection is for internal use only.
  _EnumerateEndpointDevicesAll(eRender);
  _EnumerateEndpointDevicesAll(eCapture);
  _initialized = true;
  return InitStatus::OK;
}

调用堆栈

列出设备_EnumerateEndpointDevicesAll

AudioDeviceWindowsCore::_EnumerateEndpointDevicesAll

列出某个种类的设备，采集还是播放的设备。

int32_t AudioDeviceWindowsCore::_EnumerateEndpointDevicesAll(
***
  HRESULT hr = S_OK;
  IMMDeviceCollection* pCollection = NULL;
  IMMDevice* pEndpoint = NULL;
  IPropertyStore* pProps = NULL;
  IAudioEndpointVolume* pEndpointVolume = NULL;
  LPWSTR pwszID = NULL;
  // Generate a collection of audio endpoint devices in the system.
  // Get states for *all* endpoint devices.
  // Output: IMMDeviceCollection interface.
  hr = _ptrEnumerator->EnumAudioEndpoints(
      dataFlow,  // data-flow direction (input parameter)
      DEVICE_STATE_ACTIVE | DEVICE_STATE_DISABLED | DEVICE_STATE_UNPLUGGED,
      &pCollection);  // release interface when done
  EXIT_ON_ERROR(hr);
***
  // Retrieve a count of the devices in the device collection.
  hr = pCollection->GetCount(&count);
***
  // Each loop prints the name of an endpoint device.
  for (ULONG i = 0; i < count; i++) {
    RTC_LOG(LS_VERBOSE) << "Endpoint " << i << ":";
    // Get pointer to endpoint number i.
    // Output: IMMDevice interface.
    // 拿到一个具体的设备
    hr = pCollection->Item(i, &pEndpoint);
    CONTINUE_ON_ERROR(hr);
    // Get the endpoint ID string (uniquely identifies the device among all
    // audio endpoint devices)
    hr = pEndpoint->GetId(&pwszID);
    CONTINUE_ON_ERROR(hr);
    RTC_LOG(LS_VERBOSE) << "ID string    : " << pwszID;
    // Retrieve an interface to the device's property store.
    // Output: IPropertyStore interface. 获取设备属性
    hr = pEndpoint->OpenPropertyStore(STGM_READ, &pProps);
    CONTINUE_ON_ERROR(hr);
    // use the IPropertyStore interface...
    PROPVARIANT varName;
    // Initialize container for property value.
    PropVariantInit(&varName);
    // Get the endpoint's friendly-name property.
    // Example: "Speakers (Realtek High Definition Audio)"
    hr = pProps->GetValue(PKEY_Device_FriendlyName, &varName);
    CONTINUE_ON_ERROR(hr);
    RTC_LOG(LS_VERBOSE) << "friendly name: \"" << varName.pwszVal << "\"";
// 获取设备的状态
    // Get the endpoint's current device state
    DWORD dwState;
    hr = pEndpoint->GetState(&dwState);
    CONTINUE_ON_ERROR(hr);
    if (dwState & DEVICE_STATE_ACTIVE)
      RTC_LOG(LS_VERBOSE) << "state (0x" << rtc::ToHex(dwState)
                          << ")  : *ACTIVE*";
    if (dwState & DEVICE_STATE_DISABLED)
      RTC_LOG(LS_VERBOSE) << "state (0x" << rtc::ToHex(dwState)
                          << ")  : DISABLED";
    if (dwState & DEVICE_STATE_NOTPRESENT)
      RTC_LOG(LS_VERBOSE) << "state (0x" << rtc::ToHex(dwState)
                          << ")  : NOTPRESENT";
    if (dwState & DEVICE_STATE_UNPLUGGED)
      RTC_LOG(LS_VERBOSE) << "state (0x" << rtc::ToHex(dwState)
                          << ")  : UNPLUGGED";
    // Check the hardware volume capabilities.
    DWORD dwHwSupportMask = 0;
    hr = pEndpoint->Activate(__uuidof(IAudioEndpointVolume), CLSCTX_ALL, NULL,
                             (void**)&pEndpointVolume);
    CONTINUE_ON_ERROR(hr);
    // 获取掩码从而得知支持什么控制
    hr = pEndpointVolume->QueryHardwareSupport(&dwHwSupportMask); 
    CONTINUE_ON_ERROR(hr);
    if (dwHwSupportMask & ENDPOINT_HARDWARE_SUPPORT_VOLUME)
      // The audio endpoint device supports a hardware volume control
      RTC_LOG(LS_VERBOSE) << "hwmask (0x" << rtc::ToHex(dwHwSupportMask)
                          << ") : HARDWARE_SUPPORT_VOLUME";
    if (dwHwSupportMask & ENDPOINT_HARDWARE_SUPPORT_MUTE)
      // The audio endpoint device supports a hardware mute control
      RTC_LOG(LS_VERBOSE) << "hwmask (0x" << rtc::ToHex(dwHwSupportMask)
                          << ") : HARDWARE_SUPPORT_MUTE";
    if (dwHwSupportMask & ENDPOINT_HARDWARE_SUPPORT_METER)
      // The audio endpoint device supports a hardware peak meter
      RTC_LOG(LS_VERBOSE) << "hwmask (0x" << rtc::ToHex(dwHwSupportMask)
                          << ") : HARDWARE_SUPPORT_METER";
    // Check the channel count (#channels in the audio stream that enters or
    // leaves the audio endpoint device)
    UINT nChannelCount(0);
    hr = pEndpointVolume->GetChannelCount(&nChannelCount);
    CONTINUE_ON_ERROR(hr);
    RTC_LOG(LS_VERBOSE) << "#channels    : " << nChannelCount;
    if (dwHwSupportMask & ENDPOINT_HARDWARE_SUPPORT_VOLUME) {
      // Get the volume range.
      float fLevelMinDB(0.0);
      float fLevelMaxDB(0.0);
      float fVolumeIncrementDB(0.0);
      hr = pEndpointVolume->GetVolumeRange(&fLevelMinDB, &fLevelMaxDB,
                                           &fVolumeIncrementDB);
***
***
      // Get information about the current step in the volume range.
      // This method represents the volume level of the audio stream that enters
      // or leaves the audio endpoint device as an index or "step" in a range of
      // discrete volume levels. Output value nStepCount is the number of steps
      // in the range. Output value nStep is the step index of the current
      // volume level. If the number of steps is n = nStepCount, then step index
      // nStep can assume values from 0 (minimum volume) to n ?1 (maximum
      // volume).
      UINT nStep(0);
      UINT nStepCount(0); // 获取音量步长
      hr = pEndpointVolume->GetVolumeStepInfo(&nStep, &nStepCount);
      CONTINUE_ON_ERROR(hr);
      RTC_LOG(LS_VERBOSE) << "volume steps : " << nStep << " (nStep), "
                          << nStepCount << " (nStepCount)";
    }
****
}