Media Types
All content types received or delivered by a codec can be defined by a handful of properties. Those properties define a media type, or format, which includes a major type, a subtype, and some configuration information, the format of which varies by subtype. Both major types and subtypes are identified using globally unique identifiers (GUIDs).
When working with the Windows Media Audio and Video codecs, the only major types that are used are audio and video.
A subtype identifies the method by which the content is digitally represented. For example, the subtype of compressed content identifies the codec that was used for compression. Subtypes are also used to identify uncompressed media. For example, a common type of uncompressed media is RGB video, which includes a full, pixel-by-pixel representation of every frame in the video. Several subtypes are used to describe RGB video. The subtype assigned to the content depends upon the number of bits used to describe the color of individual pixels.
The properties used to define a media type varies by major type and subtype. For video, this information includes the dimensions of a frame of video in pixels, the number of video frames per second, and similar statistics. For audio, it includes the size of individual audio samples in bits, the sample rate, and statistics such as frequency.
All of the information about a media type is sent to or from a codec by using either a DMO_MEDIA_TYPE structure (if using the codec as a DirectX media object) or an IMFMediaType object (if using the codec an IMFTransform object).
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Build date: 4/7/2010