IMediaObject::GetOutputType method (mediaobj.h)

Статья
4/26/2023

[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 It has been superseded by MediaPlayer, IMFMediaEngine, and Audio/Video Capture in Media Foundation.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.]

The GetOutputType method retrieves a preferred media type for a specified output stream.

Syntax

HRESULT GetOutputType(
        DWORD          dwOutputStreamIndex,
        DWORD          dwTypeIndex,
  [out] DMO_MEDIA_TYPE *pmt
);

Parameters

dwOutputStreamIndex

Zero-based index of an output stream on the DMO.

dwTypeIndex

Zero-based index on the set of acceptable media types.

[out] pmt

Pointer to a DMO_MEDIA_TYPE structure allocated by the caller, or NULL. If this parameter is non-NULL, the method fills the structure with the media type. You can use the value NULL to test whether the type index is in range, by checking the return code.

Return value

Returns an HRESULT value. Possible values include those in the following table.

Return code	Description
DMO_E_INVALIDSTREAMINDEX	Invalid stream index.
DMO_E_NO_MORE_ITEMS	Type index is out of range.
E_OUTOFMEMORY	Insufficient memory.
E_POINTER	NULL pointer argument.
S_OK	Success.

Remarks

Call this method to enumerate an output stream's preferred media types. The DMO assigns each media type an index value, in order of preference. The most preferred type has an index of zero. To enumerate all the types, make successive calls while incrementing the type index, until the method returns DMO_E_NO_MORE_ITEMS. The DMO is not guaranteed to enumerate every media type that it supports.

The format block in the returned type might be NULL. If so, the format type is GUID_NULL. You should check the format type before dereferencing the format block.

If the method succeeds, call MoFreeMediaType to free the format block. (This function is also safe to call when the format block is NULL.)

To set the media type, call the IMediaObject::SetOutputType method. Setting the media type on one stream can change another stream's preferred types. In fact, a stream might not have a preferred type until the type is set on another stream. For example, a decoder might not have a preferred output type until the input type is set. However, the DMO is not required to update its preferred types dynamically in this fashion. Thus, the types returned by this method are not guaranteed to be valid; they might fail when used in the SetOutputType method.

To test whether a particular media type is acceptable, call SetOutputType with the DMO_SET_TYPEF_TEST_ONLY flag.

To test whether the dwTypeIndex parameter is in range, set pmt to NULL. The method returns S_OK if the index is in range, or DMO_E_NO_MORE_ITEMS if the index is out of range.

Requirements

Requirement	Value
Target Platform	Windows
Header	mediaobj.h (include Dmo.h)
Library	Dmoguids.lib

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