WM_MEDIA_TYPE structure

The WM_MEDIA_TYPE structure is the primary structure used to describe media formats for the objects of the Windows Media Format SDK. For more information about media formats and what they are used for, see Formats.

Syntax


typedef struct _WMMediaType {
  GUID                     majortype;
  GUID                     subtype;
  BOOL                     bFixedSizeSamples;
  BOOL                     bTemporalCompression;
  ULONG                    lSampleSize;
  GUID                     formattype;
  IUnknown                 *pUnk;
  ULONG                    cbFormat;
  [size_is(cbFormat)] BYTE *pbFormat;
} WM_MEDIA_TYPE;

Members

majortype

Major type of the media sample. For example, WMMEDIATYPE_Video specifies a video stream. For a list of possible major media types, see Media Types.

subtype

Subtype of the media sample. The subtype defines a specific format (usually an encoding scheme) within a major media type. For example, WMMEDIASUBTYPE_WMV3 specifies a video stream encoded with the Windows Media Video 9 codec. Subtypes can be uncompressed or compressed. For lists of possible media subtypes, see Uncompressed Media Subtypes and Compressed Media Subtypes.

bFixedSizeSamples

Set to true if the samples are of a fixed size. Compressed audio samples are of a fixed size while video samples are not.

bTemporalCompression

Set to true if the samples are temporally compressed. Temporal compression is compression where some samples describe the changes in content from the previous sample, instead of describing the sample in its entirety. Only compressed video can be temporally compressed. By definition, no media type can use both fixed sized samples and temporal compression.

lSampleSize

Long integer containing the size of the sample, in bytes. This member is used only if bFixedSizeSamples is true.

formattype

GUID of the format type. The format type specifies the additional structure used to identify the media format. This structure is pointed to by pbFormat.

pUnk

Not used. Should be NULL.

cbFormat

Size, in bytes, of the structure pointed to by pbFormat.

pbFormat

Pointer to the format structure of the media type. The structure referenced is determined by the format type GUID. Format types include:

Media TypeStructure
WMFORMAT_VideoInfo WMVIDEOINFOHEADER
WMFORMAT_WaveFormatEx WAVEFORMATEX
WMFORMAT_MPEG2Video WMMPEG2VIDEOINFO
WMFORMAT_WebStream WMT_WEBSTREAM_FORMAT
WMFORMAT_Script WMSCRIPTFORMAT

 

Remarks

This is the same as the DirectShow structure AM_MEDIA_TYPE but is redefined in this SDK to avoid conflict with DirectShow names.

Requirements

Minimum supported client

Windows 2000 Professional [desktop apps only]

Minimum supported server

Windows 2000 Server [desktop apps only]

Version

Windows Media Format 7 SDK, or later versions of the SDK

Header

Wmsdkidl.h (include Wmsdk.h)

See also

IWMMediaProps::GetMediaType
IWMMediaProps::SetMediaType
Media Type Identifiers
Media Types
Structures

 

 

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