Media Type Functions

The Mtype.h header file in the DirectShow base classes provides helper functions for handling media types. These general-purpose functions create, copy and delete a task-allocated AM_MEDIA_TYPE structure. This is useful when using the IEnumMediaTypes interface, because the implementation allocates the structures that must be deleted later.

The functions are paired as follows:

• CreateMediaType is the opposite of DeleteMediaType.
• FreeMediaType is the opposite of CopyMediaType.

Function	Description
AreEqualVideoTypes	Compares the format, height, and width of two video sources.
CopyMediaType	Copies a task-allocated AM_MEDIA_TYPE structure.
CreateAudioMediaType	Initializes a media type structure given a wave format structure.
CreateMediaType	Allocates and initializes an AM_MEDIA_TYPE structure.
DeleteMediaType	Deletes a task-allocated AM_MEDIA_TYPE structure.
FreeMediaType	Frees a task-allocated AM_MEDIA_TYPE structure from memory.

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AreEqualVideoTypes

Media Type Functions

Determines if two media types have the same video format, width, and height.

BOOL WINAPI AreEqualVideoTypes (
  CMediaType *pmt1,
  CMediaType *pmt2
  );

Parameters

pmt1

First media type to compare.

pmt2

Second media type to compare.

Return Values

Returns TRUE if pmt1 and pmt2 have the same video format, width, and height or FALSE otherwise.

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CopyMediaType

Media Type Functions

Copies a task-allocated AM_MEDIA_TYPE structure.

void WINAPI CopyMediaType(
  AM_MEDIA_TYPE *pmtTarget,
  const AM_MEDIA_TYPE *pmtSource
  );

Parameters

pmtTarget

Pointer to an area of memory in which to place the new copy of the structure.

pmtSource

Pointer to a source structure to copy.

Return Values

No return value.

Remarks

Free the resources in the pmtTarget structure by calling FreeMediaType when your code is done with the structure.

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CreateAudioMediaType

Media Type Functions

Initializes a media type structure given a wave format structure.

STDAPI CreateAudioMediaType(
  const WAVEFORMATEX *pwfx,
  AM_MEDIA_TYPE *pmt,
  BOOL bSetFormat
  );

Parameters

pwfx

Pointer to the supplied WAVEFORMATEX structure.

pmt

Pointer to the AM_MEDIA_TYPE structure to initialize.

bSetFormat

Flag indicating whether to initialize the format section of the AM_MEDIA_TYPE structure, specifically the cbFormat and pbFormat members. Specify TRUE to initialize the format section, FALSE otherwise.

Return Values

Returns E_OUTOFMEMORY if memory could not be allocated for the format data; S_OK otherwise.

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CreateMediaType

Media Type Functions

Creates a task-allocated AM_MEDIA_TYPE structure.

AM_MEDIA_TYPE * WINAPI CreateMediaType(
  AM_MEDIA_TYPE const *pSrc
  );

Parameters

pSrc

Pointer to an AM_MEDIA_TYPE source structure.

Return Values

Returns a new AM_MEDIA_TYPE structure, or NULL if there is an error.

Remarks

Free the structure and resources allocated by this routine by calling DeleteMediaType when your code is done with the structure.

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DeleteMediaType

Media Type Functions

Deletes a task-allocated AM_MEDIA_TYPE structure.

void WINAPI DeleteMediaType(
  AM_MEDIA_TYPE *pmt
  );

Parameters

pmt

Pointer to an AM_MEDIA_TYPE structure.

Return Values

No return value.

Remarks

The structure should have been created by a call to CreateMediaType.

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FreeMediaType

Media Type Functions

Frees a task-allocated AM_MEDIA_TYPE structure from memory.

void WINAPI FreeMediaType(
  AM_MEDIA_TYPE& mt
  );

Parameters

mt

Address of the structure.

Return Values

No return value.

Remarks

The structure should have been initialized by a call to CopyMediaType.

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