Questions about IDeckLinkVideoConversion::ConvertFrame

Hello,

I am trying to create a new IDeckLinkVideoFrame object for the purposes of having a destination frame for the IDeckLinkVideoConversion::ConvertFrame method. The devices that I'm using do not support output so I cannot use the IDeckLinkOutput::CreateVideoFrame method as indicated in the spec. The alternative to this is:

The destination frame can be created by subclassing IDeckLinkVideoFrame and setting properties directly in the subclassed object.

I'm having a little trouble understanding what this is saying as even if I subclass this, I'm not sure how to even access the properties or what they are called since they are hidden.

Thanks,

Zach

To subclass the IDeckLinkVideoFrame, I'm forced to implement all of the pure virtual methods even if I don't know how these are implemented under the covers. Am I really expected to do this? When I try to convert the 10bit yuv frame to an 8bit yuv frame, I get an EXC_BAD_ACCESS error.



I have included code that represents how I subclass the IDeckLinkVideoFrame and how I instantiate and use that new object.

Header file:

Code: Select all

class MTBM8BitYUVVideoFrame : public IDeckLinkVideoFrame
{
private:
    long            _width;
    long            _height;
    BMDPixelFormat  _pixelFormat;
    BMDFrameFlags   _frameFlags;
    void *         _bufferPointer;

public:
   
    MTBM8BitYUVVideoFrame(long width, long height, BMDPixelFormat pixelFormat, BMDFrameFlags flags);
    virtual ~MTBM8BitYUVVideoFrame();
   
    //override these methods for virtual
    virtual long GetWidth (void);
    virtual long GetHeight (void);
    virtual long GetRowBytes (void);
    virtual BMDPixelFormat GetPixelFormat (void);
    virtual BMDFrameFlags GetFlags (void);
    virtual HRESULT GetBytes (/* out */ void **buffer);

    //Dummy implementations of remaining virtual methods
    virtual HRESULT GetTimecode (/* in */ BMDTimecodeFormat format, /* out */ IDeckLinkTimecode **timecode) { return E_NOINTERFACE; };
    virtual HRESULT GetAncillaryData (/* out */ IDeckLinkVideoFrameAncillary **ancillary) { return E_NOINTERFACE; } ;
   
   
    //
    // IUnknown interface (dummy implementation)
    //
   
    virtual HRESULT      QueryInterface (REFIID iid, LPVOID *ppv)   {return E_NOINTERFACE;}
    virtual ULONG      AddRef ()                           {return 1;}
    virtual ULONG      Release ()                           {return 1;}
};



CPP file

Code: Select all


MTBM8BitYUVVideoFrame::MTBM8BitYUVVideoFrame(long width, long height, BMDPixelFormat pixelFormat, BMDFrameFlags frameFlags)
{
    _width = width;
    _height = height;
    _pixelFormat = pixelFormat;
    _frameFlags = frameFlags;
   
    //this pointer size is only valid for bmdFormat8BitYUV
    switch (_pixelFormat) {
        case bmdFormat8BitYUV:
            _bufferPointer = malloc((_width * 16 / 8) * _height);
            break;
        default:
            break;
    }
   

}

MTBM8BitYUVVideoFrame::~MTBM8BitYUVVideoFrame()
{
    free(_bufferPointer);
}

long MTBM8BitYUVVideoFrame::GetWidth()
{
    return _width;
}

long MTBM8BitYUVVideoFrame::GetHeight()
{
    return _height;
}

long MTBM8BitYUVVideoFrame::GetRowBytes()
{
    return (long)(_width * 16 / 8);
}

BMDPixelFormat MTBM8BitYUVVideoFrame::GetPixelFormat()
{
    return _pixelFormat;
}

BMDFrameFlags MTBM8BitYUVVideoFrame::GetFlags()
{
    return _frameFlags;
}

HRESULT MTBM8BitYUVVideoFrame::GetBytes (/* out */ void **buffer)
{
   
    buffer = &_bufferPointer;
   
    return S_OK;
}


I use this new class as follows

Code: Select all

    MTBM8BitYUVVideoFrame *eightBitVideoFrame = new MTBM8BitYUVVideoFrame(tenBitVideoFrame->GetWidth(),tenBitVideoFrame->GetHeight(),bmdFormat8BitYUV,tenBitVideoFrame->GetFlags());
 
    IDeckLinkVideoConversion *videoConverter = CreateVideoConversionInstance();
    HRESULT convertResult = videoConverter->ConvertFrame(tenBitVideoFrame,(IDeckLinkVideoFrame*)eightBitVideoFrame);


If anyone comes across this, I was able to fix the issue by changing:

Code: Select all

buffer = &_bufferPointer;


to

Code: Select all

*buffer = _bufferPointer;