Multimedia Class Scheduler

The Multimedia Class Scheduler (MMCSS) service enables relative prioritization of work based on system-wide task priorities. This is intended mainly for multimedia applications. If this service is stopped, individual tasks return to their default priority.

Users expect multimedia applications to offer a smooth playback experience. If the playback has pauses or jerky movements, users are dissatisfied with the experience, and will not use that content delivery method. Early versions of media players suffered from a lack of bandwidth; but the common issue now is a lack of CPU processing time. Demand for the CPU processing time by concurrently running applications such as antivirus programs, content indexing, or email applications, can interfere with media rendering and playback.

To provide a better playback experience, the operating system provides the Multimedia Class Scheduler service to manage the CPU priorities of multimedia threads. An application registers with the Multimedia Class Scheduler service by using APIs that indicate its multimedia characteristics, which must match one of those listed by name under the following registry key:

HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\Currentversion\Multimedia\SystemProfile\Tasks

The task keys are:

  • Audio
  • Capture
  • Distribution
  • Games
  • Playback
  • Pro Audio
  • Window Manager

The task keys specify how much preference is given to each multimedia type for CPU and graphics processor resources.

The Multimedia Class Scheduler service also ensures that other concurrently running threads get an adequate portion of CPU time so that the system and other applications remain responsive. Therefore, the Multimedia Class Scheduler service reserves 20 percent of CPU time for other activity.

This service is installed by default and its startup type is Automatic. When the Multimedia Class Scheduler service is started in its default configuration, it logs on by using the Local System account.

The following component is dependent upon the Multimedia Class Scheduler service:

  • Windows Audio

Related content