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Specifies a Multimedia Class Scheduler Service (MMCSS) class for the Source Reader or Sink Writer.

Data type



To get this attribute, call IMFAttributes::GetString.

To set this attribute, call IMFAttributes::SetString.


Optionally set this attribute when you create an instance of the Source Reader or Sink Writer. The value of the attribute must be a valid MMCSS class name.

If this attribute is set, the Source Reader or Sink Writer registers all of its threads with the specified MMCSS class. The MMCSS ensures that data processing in the Source Reader or Sink Writer has priority over other system tasks.

To specify the base priority, set the MF_READWRITE_MMCSS_PRIORITY attribute. If that attribute is not set, the base priority is zero.

For audio-processing threads, the MF_READWRITE_MMCSS_CLASS_AUDIO attribute (if set) overrides this attribute.


Minimum supported client

Windows 8 [desktop apps | Windows Store apps]

Minimum supported server

Windows Server 2012 [desktop apps | Windows Store apps]



See also

Alphabetical List of Media Foundation Attributes



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