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OpenCV 读取音频代码实例

在windows7 以及OpenCV4 过后可以使用 CAP_MSMF 读取音频，但是OpenCV没有播放音频的API。代码示例如下。 本文解析OpenCVCAP_MSMF 进行文件、设备的 音频读取，学习MediaFoundation 的使用。

#include <opencv2/core.hpp>
#include <opencv2/videoio.hpp>
#include <opencv2/highgui.hpp>
#include <iostream>
using namespace cv;
using namespace std;int main(int argc, const char** argv)
{Mat videoFrame;Mat audioFrame;vector<vector<Mat>> audioData;VideoCapture cap;vector<int> params {    CAP_PROP_AUDIO_STREAM, 0,CAP_PROP_VIDEO_STREAM, -1,CAP_PROP_AUDIO_DATA_DEPTH, CV_32F   };//cap.open(file, CAP_MSMF, params);// 打开第一个音频输入设备cap.open(0, CAP_MSMF, params);if (!cap.isOpened()){cerr << "ERROR! Can't to open file: " + file << endl;return -1;}const int audioBaseIndex = (int)cap.get(CAP_PROP_AUDIO_BASE_INDEX);const int numberOfChannels = (int)cap.get(CAP_PROP_AUDIO_TOTAL_CHANNELS);cout << "CAP_PROP_AUDIO_DATA_DEPTH: " << depthToString((int)cap.get(CAP_PROP_AUDIO_DATA_DEPTH)) << endl;cout << "CAP_PROP_AUDIO_SAMPLES_PER_SECOND: " << cap.get(CAP_PROP_AUDIO_SAMPLES_PER_SECOND) << endl;cout << "CAP_PROP_AUDIO_TOTAL_CHANNELS: " << cap.get(CAP_PROP_AUDIO_TOTAL_CHANNELS) << endl;cout << "CAP_PROP_AUDIO_TOTAL_STREAMS: " << cap.get(CAP_PROP_AUDIO_TOTAL_STREAMS) << endl;int numberOfSamples = 0;int numberOfFrames = 0;audioData.resize(numberOfChannels);mfcap::AudioOutput audioOutput;audioOutput.Open((int)cap.get(CAP_PROP_AUDIO_TOTAL_CHANNELS),(int)cap.get(CAP_PROP_AUDIO_SAMPLES_PER_SECOND),16);for (;;){if (cap.grab()){//cap.retrieve(videoFrame);std::vector<const unsigned char*> planes;planes.resize(numberOfChannels);for (int nCh = 0; nCh < numberOfChannels; nCh++){cap.retrieve(audioFrame, audioBaseIndex+nCh);if (!audioFrame.empty()){audioData[nCh].push_back(audioFrame);//planes[nCh] = audioFrame.data + nCh * audioFrame.cols;}numberOfSamples+=audioFrame.cols;}} else { break; }}cout << "Number of audio samples: " << numberOfSamples << endl<< "Number of video frames: " << numberOfFrames << endl;return 0;
}

打开设备

bool CvCapture_MSMF::open(int index, const cv::VideoCaptureParameters* params)
{// 先重置环境close();if (index < 0)return false;if (params){// 开启硬件编解码加速，这里先省略，在后面的硬件加速上学习。configureHW(*params);/* configureStream 主要是配置是否捕获音频或视频流// 如果需要捕获音频流: audioStream = 0 否者 audioStream  = -1// 视频流同理，对应的变量为: videoStream*//* setAudioProperties // outputAudioFormat: 音频的位深， CV_16S 等// audioSamplesPerSecond 采样率// syncLastFrame: 是否需要音视频同步，OpenCV里面只支持视频文件的音视频同步*/if (!(configureStreams(*params) && setAudioProperties(*params)))return false;}// 仅支持打开音频流或者视频流，不能在一个对象里面打开或者都不打开。if (videoStream != -1 && audioStream != -1 || videoStream == -1 && audioStream == -1){CV_LOG_DEBUG(NULL, "Only one of the properties CAP_PROP_AUDIO_STREAM " << audioStream << " and " << CAP_PROP_VIDEO_STREAM << " must be different from -1");return false;}// DeviceList  主要检测当前系统中，视频或音频输入设备的个数，以及激活某一个设备。DeviceList devices;UINT32 count = 0;// 如果是读音频设备就枚举音频输入设备if (audioStream != -1)count = devices.read(MF_DEVSOURCE_ATTRIBUTE_SOURCE_TYPE_AUDCAP_GUID);// 读视频设备同理。值得注意的是，opencv只支持读音频或视频设备// 如果都设置为0， 则默认读视频if (videoStream != -1)count = devices.read(MF_DEVSOURCE_ATTRIBUTE_SOURCE_TYPE_VIDCAP_GUID);if (count == 0 || static_cast<UINT32>(index) > count){CV_LOG_DEBUG(NULL, "Device " << index << " not found (total " << count << " devices)");return false;}/* getDefaultSourceConfig 这个主要设置硬件加速相关，这里可以先跳过*/_ComPtr<IMFAttributes> attr = getDefaultSourceConfig();/*SourceReaderCB 读取回调设置读取回调，当设置了读取的回调之后，MediaFoundation 读取Source 为异步模式这个Open函数是读设备的，还有其他重载函数用于读文件在OpenCV里面，读取设备使用异步模式，读取文件使用同步模式。*/_ComPtr<IMFSourceReaderCallback> cb = new SourceReaderCB();attr->SetUnknown(MF_SOURCE_READER_ASYNC_CALLBACK, cb.Get());// 激活目标设备_ComPtr<IMFMediaSource> src = devices.activateSource(index);if (!src.Get() || FAILED(MFCreateSourceReaderFromMediaSource(src.Get(), attr.Get(), &videoFileSource))){CV_LOG_DEBUG(NULL, "Failed to create source reader");return false;}isOpen = true;device_status = true;camid = index;readCallback = cb;duration = 0;// 选择合适的摄像头的流，比如宽高，fps.一般一个摄像头有很多个拉流的格式// 音频设备同理，比如有不同的采样率，位深等。if (configureOutput()){frameStep = captureVideoFormat.getFrameStep();}if (isOpen && !openFinalize_(params)){close();return false;}if (isOpen){if (audioStream != -1)if (!checkAudioProperties())return false;}return isOpen;
}

选择合适的设备流 configureOutput

bool CvCapture_MSMF::configureOutput()
{// 读取设备所有的流，当然也可以读第一个流if (FAILED(videoFileSource->SetStreamSelection((DWORD)MF_SOURCE_READER_ALL_STREAMS, false))){CV_LOG_WARNING(NULL, "Failed to reset streams");return false;}bool tmp = true;// 配置视频流if (videoStream != -1)tmp = (!device_status)? configureVideoOutput(MediaType(), outputVideoFormat) : configureVideoOutput(MediaType::createDefault_Video(), outputVideoFormat);// 配置音频流if (audioStream != -1)tmp &= (!device_status)? configureAudioOutput(MediaType()) : configureAudioOutput(MediaType::createDefault_Audio());return tmp;
}

配置音频流 configureAudioOutput

bool CvCapture_MSMF::configureAudioOutput(MediaType newType)
{/*FormatStorage  存储设备的流信息，以及挑选最合适的流*/FormatStorage formats;formats.read(videoFileSource.Get());std::pair<FormatStorage::MediaID, MediaType> bestMatch;formats.countNumberOfAudioStreams(numberOfAudioStreams);if (device_status)bestMatch = formats.findBestAudioFormat(newType);elsebestMatch = formats.findAudioFormatByStream(audioStream);if (bestMatch.second.isEmpty(true)){CV_LOG_DEBUG(NULL, "Can not find audio stream with requested parameters");isOpen = false;return false;}dwAudioStreamIndex = bestMatch.first.stream;dwStreamIndices.push_back(dwAudioStreamIndex);MediaType newFormat = bestMatch.second;newFormat.majorType = MFMediaType_Audio;newFormat.nSamplesPerSec = (audioSamplesPerSecond == 0) ? 44100 : audioSamplesPerSecond;switch (outputAudioFormat){case CV_8S:newFormat.subType = MFAudioFormat_PCM;newFormat.bit_per_sample = 8;break;case CV_16S:newFormat.subType = MFAudioFormat_PCM;newFormat.bit_per_sample = 16;break;case CV_32S:newFormat.subType = MFAudioFormat_PCM;newFormat.bit_per_sample = 32;case CV_32F:newFormat.subType = MFAudioFormat_Float;newFormat.bit_per_sample = 32;break;default:break;}// 初始化流return initStream(dwAudioStreamIndex, newFormat);
}

初始化流 initStream

bool CvCapture_MSMF::initStream(DWORD streamID, const MediaType mt)
{CV_LOG_DEBUG(NULL, "Init stream " << streamID << " with MediaType " << mt);_ComPtr<IMFMediaType> mediaTypesOut;if (mt.majorType == MFMediaType_Audio){captureAudioFormat = mt;mediaTypesOut = mt.createMediaType_Audio();}if (mt.majorType == MFMediaType_Video){captureVideoFormat = mt;mediaTypesOut = mt.createMediaType_Video();}if (FAILED(videoFileSource->SetStreamSelection(streamID, true))){CV_LOG_WARNING(NULL, "Failed to select stream " << streamID);return false;}HRESULT hr = videoFileSource->SetCurrentMediaType(streamID, NULL, mediaTypesOut.Get());if (hr == MF_E_TOPO_CODEC_NOT_FOUND){CV_LOG_WARNING(NULL, "Failed to set mediaType (stream " << streamID << ", " << mt << "(codec not found)");return false;}else if (hr == MF_E_INVALIDMEDIATYPE){CV_LOG_WARNING(NULL, "Failed to set mediaType (stream " << streamID << ", " << mt << "(unsupported media type)");return false;}else if (FAILED(hr)){CV_LOG_WARNING(NULL, "Failed to set mediaType (stream " << streamID << ", " << mt << "(HRESULT " << hr << ")");return false;}return true;
}

捕获音频帧 Garb()

捕获帧的回调 SourceReaderCB

OpenCV捕获设备数据，采用异步模式，需要自定义一个捕获帧的回调

// 需要继承 IMFSourceReaderCallback
class SourceReaderCB : public IMFSourceReaderCallback
{
public:
// 最大的缓冲帧数量static const size_t MSMF_READER_MAX_QUEUE_SIZE = 3;SourceReaderCB() :m_nRefCount(0), m_hEvent(CreateEvent(NULL, FALSE, FALSE, NULL)), m_bEOS(FALSE), m_hrStatus(S_OK), m_reader(NULL), m_dwStreamIndex(0){}// COM 接口必须的，感觉就是照着格式写// IUnknown methodsSTDMETHODIMP QueryInterface(REFIID iid, void** ppv) CV_OVERRIDE{
#ifdef _MSC_VER
#pragma warning(push)
#pragma warning(disable:4838)
#endifstatic const QITAB qit[] ={QITABENT(SourceReaderCB, IMFSourceReaderCallback),{ 0 },};
#ifdef _MSC_VER
#pragma warning(pop)
#endifreturn QISearch(this, qit, iid, ppv);}STDMETHODIMP_(ULONG) AddRef() CV_OVERRIDE{return InterlockedIncrement(&m_nRefCount);}STDMETHODIMP_(ULONG) Release() CV_OVERRIDE{ULONG uCount = InterlockedDecrement(&m_nRefCount);if (uCount == 0){delete this;}return uCount;}// 在 调用wait()的时候 被调用STDMETHODIMP OnReadSample(HRESULT hrStatus, DWORD dwStreamIndex, DWORD dwStreamFlags, LONGLONG llTimestamp, IMFSample *pSample) CV_OVERRIDE{HRESULT hr = 0;cv::AutoLock lock(m_mutex);if (SUCCEEDED(hrStatus)){if (pSample){CV_LOG_DEBUG(NULL, "videoio(MSMF): got frame at " << llTimestamp);// 如果缓冲的帧的数量大于最大的数量，需要弹出前面的帧if (m_capturedFrames.size() >= MSMF_READER_MAX_QUEUE_SIZE){
#if 0CV_LOG_DEBUG(NULL, "videoio(MSMF): drop frame (not processed). Timestamp=" << m_capturedFrames.front().timestamp);m_capturedFrames.pop();
#else// this branch reduces latency if we drop frames due to slow processing.// avoid fetching of already outdated frames from the queue's front.CV_LOG_DEBUG(NULL, "videoio(MSMF): drop previous frames (not processed): " << m_capturedFrames.size());std::queue<CapturedFrameInfo>().swap(m_capturedFrames);  // similar to missing m_capturedFrames.clean();
#endif}m_capturedFrames.emplace(CapturedFrameInfo{ llTimestamp, _ComPtr<IMFSample>(pSample), hrStatus });}}else{CV_LOG_WARNING(NULL, "videoio(MSMF): OnReadSample() is called with error status: " << hrStatus);}if (MF_SOURCE_READERF_ENDOFSTREAM & dwStreamFlags){// Reached the end of the stream.m_bEOS = true;}m_hrStatus = hrStatus;if (FAILED(hr = m_reader->ReadSample(dwStreamIndex, 0, NULL, NULL, NULL, NULL))){CV_LOG_WARNING(NULL, "videoio(MSMF): async ReadSample() call is failed with error status: " << hr);m_bEOS = true;}if (pSample || m_bEOS){SetEvent(m_hEvent);}return S_OK;}STDMETHODIMP OnEvent(DWORD, IMFMediaEvent *) CV_OVERRIDE{return S_OK;}STDMETHODIMP OnFlush(DWORD) CV_OVERRIDE{return S_OK;}HRESULT Wait(DWORD dwMilliseconds, _ComPtr<IMFSample>& mediaSample, LONGLONG& sampleTimestamp, BOOL& pbEOS){pbEOS = FALSE;for (;;){{cv::AutoLock lock(m_mutex);pbEOS = m_bEOS && m_capturedFrames.empty();if (pbEOS)return m_hrStatus;if (!m_capturedFrames.empty()){CV_Assert(!m_capturedFrames.empty());CapturedFrameInfo frameInfo = m_capturedFrames.front(); m_capturedFrames.pop();CV_LOG_DEBUG(NULL, "videoio(MSMF): handle frame at " << frameInfo.timestamp);mediaSample = frameInfo.sample;CV_Assert(mediaSample);sampleTimestamp = frameInfo.timestamp;ResetEvent(m_hEvent);  // event is auto-reset, but we need this forced reset due time gap between wait() and mutex hold.return frameInfo.hrStatus;}}CV_LOG_DEBUG(NULL, "videoio(MSMF): waiting for frame... ");DWORD dwResult = WaitForSingleObject(m_hEvent, dwMilliseconds);if (dwResult == WAIT_TIMEOUT){return E_PENDING;}else if (dwResult != WAIT_OBJECT_0){return HRESULT_FROM_WIN32(GetLastError());}}}private:// Destructor is private. Caller should call Release.virtual ~SourceReaderCB(){CV_LOG_INFO(NULL, "terminating async callback");}public:long                m_nRefCount;        // Reference count.cv::Mutex           m_mutex;HANDLE              m_hEvent;BOOL                m_bEOS;HRESULT             m_hrStatus;IMFSourceReader *m_reader;DWORD m_dwStreamIndex;struct CapturedFrameInfo {LONGLONG timestamp;_ComPtr<IMFSample> sample;HRESULT hrStatus;};std::queue<CapturedFrameInfo> m_capturedFrames;
};