Multimedia Class Scheduler (MMCSS) Service Defaults in Windows 8

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 resort to their default priority.

Default Settings

Startup type:Automatic
Display name:Multimedia Class Scheduler
Service name:MMCSS
Service type:share
Error control:normal
Path:%SystemRoot%\system32\svchost.exe -k netsvcs
Registry key:HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MMCSS
  • SeIncreaseBasePriorityPrivilege
  • SeImpersonatePrivilege
  • SeDebugPrivilege

Default Behavior

Multimedia Class Scheduler is a Win32 service. In Windows 8 it is starting automatically during the operating system startup. Then the Multimedia Class Scheduler service runs as LocalSystem in a process of svchost.exe, sharing it with other services. If Multimedia Class Scheduler fails to start, the error details are added to Windows 8 error log. When the operating system startup is complete, the user is being notified that the MMCSS service hasn't been started.


If Multimedia Class Scheduler is disabled, the Windows Audio service will not be started and initialized.

Restore Default Startup Configuration for Multimedia Class Scheduler

1. Select your Windows 8 edition and update pack, and then click Download.

2. Save the Win8_MMCSS_Service_Startup.cmd file to a local storage device.

3. Run the saved file as an administrator.

4. Restart the computer.

The MMCSS service is using the mmcss.dll file that is located in the %WinDir%\system32 folder. If the file is corrupted or deleted, you can put it back in there.