如何通过UVC支持硬件编码H264

Question

I am using Logitech C930e webcam in a videochat application, created with DirectShow. So far I was able to use raw stream in YUY2 or mJPEG. Anyway, I have discovered that the webcam supports hardware H264 encoding though a UVC interface.

Right now I using standart methods to fetch possible webcam capture pin configurations, but there is no H264 pin there.

void list_cameras {
    ICreateDevEnum *pDevEnum = nullptr;
    IEnumMoniker *pEnum = nullptr;

    // Create the System Device Enumerator.
    HRESULT hr = CoCreateInstance(CLSID_SystemDeviceEnum, nullptr,
                                  CLSCTX_INPROC_SERVER, IID_ICreateDevEnum,
                                  reinterpret_cast<void**>(&pDevEnum));
    if (SUCCEEDED(hr)) {
        // Create an enumerator for the video capture category.
        hr = pDevEnum->CreateClassEnumerator(
            CLSID_VideoInputDeviceCategory,
            &pEnum, 0);
        if (hr == S_FALSE) {
            return;
        }
    }

    IMoniker *pMoniker = nullptr; // IMoniker is the device
    int index = 0;

    // for each device
    while (pEnum->Next(1, &pMoniker, nullptr) == S_OK) {

        // bind camera to filter to be able to use it
        if (cam.device->BindToObject(nullptr, nullptr, IID_IBaseFilter, reinterpret_cast<void**>(&_pCapture)) != S_OK) {
            continue;
        }

        // fetch the configuration interface
        IAMStreamConfig *pConfig = nullptr;
        HRESULT hr = _capture->FindInterface(
            &PIN_CATEGORY_CAPTURE, // Preview pin.
            nullptr, // Any media type.
            _pCapture, // Pointer to the capture filter.
            IID_IAMStreamConfig, reinterpret_cast<void**>(&pConfig));

        if (FAILED(hr)) {
            continue;
        }

        // fetch possible configurations
        int iCount = 0, iSize = 0;
        if (pConfig->GetNumberOfCapabilities(&iCount, &iSize) != S_OK) {
            continue;
        }

        // store each configuration
        AM_MEDIA_TYPE *pmtConfig;
        for (int iFormat = 0; iFormat < iCount; iFormat++) {
            // get config
            VIDEO_STREAM_CONFIG_CAPS scc;
            if (pConfig->GetStreamCaps(iFormat, &pmtConfig, reinterpret_cast<BYTE*>(&scc)) != S_OK) {
                continue;
            }

            // copy config data
            VIDEOINFOHEADER *pVih = new VIDEOINFOHEADER(); // deleted afterwards
            *pVih = *reinterpret_cast<VIDEOINFOHEADER *>(pmtConfig->pbFormat);

            AM_MEDIA_TYPE mt;
            mt = *pmtConfig;
            mt.pbFormat = reinterpret_cast<BYTE *>(pVih);
            auto fcc = FOURCCMap(pVih->bmiHeader.biCompression);

            // wrap it
            CameraConfig config = { mt, pVih->bmiHeader.biWidth, pVih->bmiHeader.biHeight, 1000 / (static_cast<float>(pVih->AvgTimePerFrame) / 10000), fcc };

            // if resolution is bad (or unsupported), skip this configuration
            if (config.width == 0 || config.height == 0 ) // bad
                continue;

            cam.configurations.push_back(config);
        }
        _cameras.push_back(cam);

        pConfig->Release();
        _pCapture->Release();
    }

    pEnum->Release();
    pDevEnum->Release();
}

_cameras is a vector of Camera, defined as follows:

typedef struct {
    //! Pointer to DirectShow device.
    DSDevice device; 

    //! Camera name
    string name;

    //! List of supported configurations.
    vector<CameraConfig> configurations; // list of all available configurations

    //! Index of selected configuration.
    int selected;
} Camera;

_pCapture is a pointer to the created capture filter. CameraConfig is defined as follows:

typedef struct {
    //! Media type.
    AM_MEDIA_TYPE _mediaType;

    //! Output width.
    int width;

    //! Outpus height.
    int height;

    //! Output framerate.
    float fps;

    //! Compression algoritm. YUY2 and mJPEG are supported for now.
    FOURCCMap compression;
} CameraConfig;

How do one implement a support for UVC devices? Which parameters of hardware encoder can be controlled?

Thanks.

Answer 1

The only way I was able to get that stream under Windows 8.x was by NOT USING LOGITECH DRIVERS. This is a UVC 1.5 compatible camera and it will be configured automatically by the OS. With that driver (from Microsoft), use pin 1 (not 0) and you will get a ton of H264 formats.

I think that under Windows 7, some drivers from Logitech give also a number of H264 formats.

In the case you are using Windows 8.x and you already have the Logitech driver installed you must remove that. And it is quite hard. I usually do it by writing constructs like this (run as admin):

BOOL res;
res = SetupUninstallOEMInf(TEXT("oem131.inf"), SUOI_FORCEDELETE, nullptr );

As to what inf you delete this is simple: go to Windows\\Inf folder and search for Logitech. Then check each file o see what exactly is (you might have a mouse or something else you want to keep). Usually it is more than one.