Unreal音频录制流程分析

先看一下录音数据的存储结构

	/************************************************************************/
	/* FAudioRecordingData                                                  */
	/* This is used by USoundSubmix and the AudioMixerBlueprintLibrary      */
	/* to contain FSoundWavePCMWriter operations.                           */
	/************************************************************************/
	struct FAudioRecordingData
	{
		TSampleBuffer<int16> InputBuffer;
		FSoundWavePCMWriter Writer;

		~FAudioRecordingData() {};
	};

其中，TSampleBuffer结构如下

template <class SampleType = DefaultUSoundWaveSampleType>
	class TSampleBuffer
	{
	private:
		// raw PCM data buffer
		TArray<SampleType> RawPCMData;
		// The number of samples in the buffer
		int32 NumSamples;
		// The number of frames in the buffer
		int32 NumFrames;
		// The number of channels in the buffer
		int32 NumChannels;
		// The sample rate of the buffer	
		int32 SampleRate;
		// The duration of the buffer in seconds
		float SampleDuration;
    }

录制音频的关键函数

USoundWave* UAudioMixerBlueprintLibrary::StopRecordingOutput(const UObject* WorldContextObject, EAudioRecordingExportType ExportType, const FString& Name, FString Path, USoundSubmix* SubmixToRecord, USoundWave* ExistingSoundWaveToOverwrite)
{
	if (RecordingData.IsValid())
	{
		UE_LOG(LogAudioMixer, Warning, TEXT("Abandoning existing write operation. If you'd like to export multiple submix recordings at the same time, use Start/Finish Recording Submix Output instead."));
	}

	if (Audio::FMixerDevice* MixerDevice = FAudioDeviceManager::GetAudioMixerDeviceFromWorldContext(WorldContextObject))
	{
		float SampleRate;
		float ChannelCount;

		// call the thing here.
		Audio::FAlignedFloatBuffer& RecordedBuffer = MixerDevice->StopRecording(SubmixToRecord, ChannelCount, SampleRate);

		if (RecordedBuffer.Num() == 0)
		{
			UE_LOG(LogAudioMixer, Warning, TEXT("No audio data. Did you call Start Recording Output?"));
			return nullptr;
		}

		// Pack output data into a TSampleBuffer and record out:
		RecordingData.Reset(new Audio::FAudioRecordingData());
		RecordingData->InputBuffer = Audio::TSampleBuffer<int16>(RecordedBuffer, ChannelCount, SampleRate);

		switch (ExportType)
		{
		case EAudioRecordingExportType::SoundWave:
		{
			USoundWave* ResultingSoundWave = RecordingData->Writer.SynchronouslyWriteSoundWave(RecordingData->InputBuffer, &Name, &Path);
			RecordingData.Reset();
			return ResultingSoundWave;
			break;
		}
		case EAudioRecordingExportType::WavFile:
		{
			RecordingData->Writer.BeginWriteToWavFile(RecordingData->InputBuffer, Name, Path, [SubmixToRecord]()
			{
				if (SubmixToRecord && SubmixToRecord->OnSubmixRecordedFileDone.IsBound())
				{
					SubmixToRecord->OnSubmixRecordedFileDone.Broadcast(nullptr);
				}

				// I'm gonna try this, but I do not feel great about it.
				RecordingData.Reset();
			});
			break;
		}
		default:
			break;
		}	
	}
	else
	{
		UE_LOG(LogAudioMixer, Error, TEXT("Output recording is an audio mixer only feature."));
	}

	return nullptr;
}