Overview of Media Types
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4/8/2010
Three main pieces of information describe a media type:
- Major type. A globally unique identifier (GUID) that defines a broad category for the data, such as audio or video.
- Subtype. A GUID that defines more specific aspects of the type, such as 24-bit RGB for video data.
- Format block. A type-specific structure that fully specifies the format.
For more information, see the DMO_MEDIA_TYPE structure.
When an application first creates an instance of a DMO, the streams in the DMO have no particular media type. Before the application can use the DMO to process data, it must specify media types for all the streams. (Optional streams are an exception; see Discardable and Optional Streams.)
To find an acceptable media type for a particular stream, the application queries the DMO. The DMO enumerates possible types, and the application selects one.
Setting a media type on one stream can change the possible types available for other streams. For example, an audio-effect DMO might support a range of sample rates, but require the output rate to match the input rate. Setting the input type would therefore restrict the set of possible output types.