IEnumMediaTypes Interface

The IEnumMediaTypes interface enumerates the preferred formats for a pin.

When to Implement

This interface must be implemented and made available by the IPin::EnumMediaTypes method. The CBasePin::EnumMediaTypes member function automatically does this in the DirectShow™ class library and uses the CEnumMediaTypes class to create the enumerator object.

When to Use

This interface is normally used by a connecting pin to determine the media type when negotiating a connection. It can also be passed through to other pins, either upstream or downstream of the filter, when intervening filters do not have a list of preferred media types. For example, a transform-inplace filter might pass the IEnumMediaTypes interface of a downstream input pin to the connecting output pin of the upstream filter, instead of providing its own IEnumMediaTypes interface.

Methods in Vtable Order

IUnknown methods	Description
QueryInterface	Returns pointers to supported interfaces.
AddRef	Increments the reference count.
Release	Decrements the reference count.

IEnumMediaTypes methods	Description
Next	Retrieves the specified number of items in the enumeration sequence.
Skip	Skips a specified number of elements in the enumeration sequence.
Reset	Resets the enumeration sequence to the beginning.
Clone	Returns another enumerator containing the same enumeration state as the current one.

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IEnumMediaTypes::Clone

IEnumMediaTypes Interface

Returns another enumerator containing the same enumeration state as the current one.

HRESULT Clone(
  IEnumMediaTypes ** ppEnum
  );

Parameters

ppEnum

[out] New copy of the enumerator.

Return Values

Returns an HRESULT value that depends on the implementation. HRESULT can be one of the following standard constants, or other values not listed:

Value	Meaning
E_FAIL	Failure.
E_POINTER	Null pointer argument.
E_INVALIDARG	Invalid argument.
E_NOTIMPL	Method isn't supported.
S_OK or NOERROR	Success.

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IEnumMediaTypes::Next

IEnumMediaTypes Interface

Retrieves the specified number of items in the enumeration sequence.

HRESULT Next(
  ULONG cMediaTypes,
  AM_MEDIA_TYPE ** ppMediaTypes,
  ULONG * pcFetched
  );

Parameters

cMediaTypes

[in] Number of media types to place.

ppMediaTypes

[out] Array in which to place the pointers to the next media type.

pcFetched

[out] Actual count passed.

Return Values

Returns an HRESULT value that depends on the implementation. HRESULT can be one of the following standard constants, or other values not listed:

Value	Meaning
E_FAIL	Failure.
E_POINTER	Null pointer argument.
E_INVALIDARG	Invalid argument.
E_NOTIMPL	Method isn't supported.
S_OK or NOERROR	Success.

Remarks

To use this method, pass an array of pointers to media types. (If you want only a single media type, you can pass a pointer to a media type pointer in place of an array of media type pointers.) The interface allocates the necessary AM_MEDIA_TYPE structures and initializes them with the variable format block. Free each media type by calling DeleteMediaType, which will free the format block and the media type itself.

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IEnumMediaTypes::Reset

IEnumMediaTypes Interface

Resets the enumerator to the beginning so that the next call to the IEnumMediaTypes::Next method returns, at a minimum, the first media type (if any) in the enumeration.

HRESULT Reset(void);

Return Values

Returns S_OK if successful; otherwise, returns S_FALSE.

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IEnumMediaTypes::Skip

IEnumMediaTypes Interface

Skips a specified number of elements in the enumeration sequence.

HRESULT Skip(
  ULONG cMediaTypes
  );

Parameters

cMediaTypes

[in] Number of media type elements to skip.

Return Values

Returns an HRESULT value that depends on the implementation. HRESULT can be one of the following standard constants, or other values not listed:

Value	Meaning
E_FAIL	Failure.
E_POINTER	Null pointer argument.
E_INVALIDARG	Invalid argument.
E_NOTIMPL	Method isn't supported.
S_OK or NOERROR	Success.

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