【MediaFoundation】OpenCV VideoCapture 读取音频源码

本文介绍: 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。

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);
    else
        bestMatch = 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 methods
    STDMETHODIMP QueryInterface(REFIID iid, void** ppv) CV_OVERRIDE
    {
#ifdef _MSC_VER
#pragma warning(push)
#pragma warning(disable:4838)
#endif
        static const QITAB qit[] =
        {
            QITABENT(SourceReaderCB, IMFSourceReaderCallback),
            { 0 },
        };
#ifdef _MSC_VER
#pragma warning(pop)
#endif
        return 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 0
                    CV_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;
};