Enumerating Media Types
[The feature associated with this page, DirectShow, is a legacy feature. It has been superseded by MediaPlayer, IMFMediaEngine, and Audio/Video Capture in Media Foundation. Those features have been optimized for Windows 10 and Windows 11. Microsoft strongly recommends that new code use MediaPlayer, IMFMediaEngine and Audio/Video Capture in Media Foundation instead of DirectShow, when possible. Microsoft suggests that existing code that uses the legacy APIs be rewritten to use the new APIs if possible.]
Pins support the IPin::EnumMediaTypes method, which enumerates a pin's preferred media types. It returns a pointer to the IEnumMediaTypes interface. The IEnumMediaTypes::Next method retrieves pointers to AM_MEDIA_TYPE structures describing media types.
The media type enumerator exists primarily to help the Filter Graph Manager make intelligent connections, and your applications will probably not use it. A pin does not necessarily return any preferred media types. Moreover, the media types it returns might depend on the filter's connection status. For example, a filter's output pin might return a different set of media types depending on which media type was set for the filter's input pin.
The following example finds a preferred media type that matches a specified major type, subtype, or format type.
// Given a pin, find a preferred media type
//
// pPin Pointer to the pin.
// majorType Preferred major type (GUID_NULL = don't care).
// subType Preferred subtype (GUID_NULL = don't care).
// formatType Preferred format type (GUID_NULL = don't care).
// ppmt Receives a pointer to the media type. Can be NULL.
//
// Note: If you want to check whether a pin supports a desired media type,
// but do not need the format details, set ppmt to NULL.
//
// If ppmt is not NULL and the method succeeds, the caller must
// delete the media type, including the format block.
HRESULT GetPinMediaType(
IPin *pPin, // pointer to the pin
REFGUID majorType, // desired major type, or GUID_NULL = don't care
REFGUID subType, // desired subtype, or GUID_NULL = don't care
REFGUID formatType, // desired format type, of GUID_NULL = don't care
AM_MEDIA_TYPE **ppmt // Receives a pointer to the media type. (Can be NULL)
)
{
*ppmt = NULL;
IEnumMediaTypes *pEnum = NULL;
AM_MEDIA_TYPE *pmt = NULL;
BOOL bFound = FALSE;
HRESULT hr = pPin->EnumMediaTypes(&pEnum);
if (FAILED(hr))
{
return hr;
}
while (hr = pEnum->Next(1, &pmt, NULL), hr == S_OK)
{
if ((majorType == GUID_NULL) || (majorType == pmt->majortype))
{
if ((subType == GUID_NULL) || (subType == pmt->subtype))
{
if ((formatType == GUID_NULL) ||
(formatType == pmt->formattype))
{
// Found a match.
if (ppmt)
{
*ppmt = pmt; // Return it to the caller
}
else
{
_DeleteMediaType(pmt);
}
bFound = TRUE;
break;
}
}
}
_DeleteMediaType(pmt);
}
SafeRelease(&pEnum);
if (SUCCEEDED(hr))
{
if (!bFound)
{
hr = VFW_E_NOT_FOUND;
}
}
return hr;
}
Note
This example uses the SafeRelease function to release interface pointers.
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