Media Type Conversions

Occasionally it is necessary to convert between Media Foundation media types and the older media type structures from DirectShow or the Windows Media Format SDK.

From a Format Structure to a Media Foundation Type

The following functions initialize a Media Foundation media type from a format structure. These functions are also useful if a data stream or a file header contains a format structure. For example, the file header for WAVE audio files contains a WAVEFORMATEX structure.

From a Media Foundation Type to a Format Structure

The following functions create or initialize a format structure from a Media Foundation media type.

Format Mappings

The following tables list the Media Foundation attributes that correspond to various format structures. Not all of these attributes can be translated directly. To perform conversions, you should use the functions listed in the previous section; these tables are provided mainly for reference.

AM_MEDIA_TYPE

WAVEFORMATEX, WAVEFORMATEXTENSIBLE

VIDEOINFOHEADER, VIDEOINFOHEADER2

The following attributes can be inferred from the VIDEOINFOHEADER or VIDEOINFOHEADER2 structure but also require some knowledge of the format details. For example, different YUV formats have different stride requirements.

• MF_MT_DEFAULT_STRIDE
• MF_MT_MINIMUM_DISPLAY_APERTURE
• MF_MT_PAN_SCAN_APERTURE

MPEG1VIDEOINFO

MPEG2VIDEOINFO

Examples

The following code fills in a BITMAPINFOHEADER structure from a video media type. Note that this conversions loses some of the format information (interlacing, frame rate, extended color data). However, it might be useful when saving a bitmap from a video frame, for example.

#include <dshow.h>
#include <dvdmedia.h>

// Converts a video type to a BITMAPINFO structure.
// The caller must free the structure by calling CoTaskMemFree.

// Note that this conversion loses some format information, including 
// interlacing, and frame rate.

HRESULT GetBitmapInfoHeaderFromMFMediaType(
    IMFMediaType *pType,            // Pointer to the media type.
    BITMAPINFOHEADER **ppBmih,      // Receives a pointer to the structure. 
    DWORD *pcbSize)                 // Receives the size of the structure.
{
    *ppBmih = NULL;
    *pcbSize = 0;

    GUID majorType = GUID_NULL;
    AM_MEDIA_TYPE *pmt = NULL;
    DWORD cbSize = 0;
    DWORD cbOffset = 0;
    BITMAPINFOHEADER *pBMIH = NULL;

    // Verify that this is a video type.
    HRESULT hr = pType->GetMajorType(&majorType);
    if (FAILED(hr))
    {
        goto done;
    }

    if (majorType != MFMediaType_Video)
    {
        hr = MF_E_INVALIDMEDIATYPE;
        goto done;
    }

    hr = pType->GetRepresentation(AM_MEDIA_TYPE_REPRESENTATION, (void**)&pmt);
    if (FAILED(hr))
    {
        goto done;
    }

    if (pmt->formattype == FORMAT_VideoInfo)
    {
        cbOffset = (FIELD_OFFSET(VIDEOINFOHEADER,bmiHeader));
    }
    else if (pmt->formattype == FORMAT_VideoInfo2)
    {
        cbOffset = (FIELD_OFFSET(VIDEOINFOHEADER2,bmiHeader));
    }
    else
    {
        hr = MF_E_INVALIDMEDIATYPE; // Unsupported format type.
        goto done;
    }

    if (pmt->cbFormat - cbOffset < sizeof(BITMAPINFOHEADER))
    {
        hr = E_UNEXPECTED; // Bad format size. 
        goto done;
    }

    cbSize = pmt->cbFormat - cbOffset;

    pBMIH = (BITMAPINFOHEADER*)CoTaskMemAlloc(cbSize);
    if (pBMIH == NULL)
    {
        hr = E_OUTOFMEMORY;
        goto done;
    }
    
    CopyMemory(pBMIH, pmt->pbFormat + cbOffset, cbSize);
    
    *ppBmih = pBMIH;
    *pcbSize = cbSize;

done:
    if (pmt)
    {
        pType->FreeRepresentation(AM_MEDIA_TYPE_REPRESENTATION, pmt);
    }
    return hr;
}

Related topics

Media Types