Multimedia Class Scheduler Service (MMCSS) is a

Windows service In Windows NT operating systems, a Windows service is a computer program that operates in the background. It is similar in concept to a Unix daemon. A Windows service must conform to the interface rules and protocols of the Service Control Manag ...

that allows multimedia applications to get prioritized access to CPU for time-sensitive processing (such as multimedia applications) as well as prioritized disc access to ensure that the process is not starved of data to process. The MMCSS service monitors the CPU load and dynamically adjusts priority so that the application can use as much

CPU time CPU time (or process time) is the amount of time that a central processing unit (CPU) was used for processing instructions of a computer program or operating system. CPU time is measured in clock ticks or seconds. Sometimes it is useful to con ...

as possible without denying CPU to lower priority applications. MMCSS uses heuristics to determine the relative priority required for the task the thread is performing and dynamically adjusts priority based on that. A thread must invoke MMCSS explicitly to use its services by calling the AvSetMmMaxThreadCharacteristics() or AvSetMmThreadCharacteristics()

API An application programming interface (API) is a connection between computers or between computer programs. It is a type of software interface, offering a service to other pieces of software. A document or standard that describes how to build ...

s. MMCSS is used by the multimedia applications in

Windows Vista Windows Vista is a major release of the Windows NT operating system developed by Microsoft. It was the direct successor to Windows XP, released five years earlier, which was then the longest time span between successive releases of Microsoft W ...

, including

Windows Media Player Windows Media Player (WMP, officially referred to as Windows Media Player Legacy to retronym, distinguish it from Windows Media Player (2022), the new Windows Media Player introduced with Windows 11) is the first media player (application soft ...

and

Windows Media Center Windows Media Center (WMC) is a discontinued digital video recorder and media player created by Microsoft. Media Center was first introduced to Windows in 2002 on Windows XP Media Center Edition (MCE). It was included in Home Premium and U ...

to provide glitch-free audio playback.

Problems

This service has been implicated in poor networking performance while multimedia is playing. In response to this, Microsoft has included a configurable optionMicrosoft Knowledge base article 948066
/ref> in Windows Vista Service Pack 1 and later where users can specify the network throttling index value for the Multimedia Class Scheduling Service so that network performance and audio/video playback quality can be balanced according to how users configure it.

References

Windows audio Windows services {{Windows-stub

Problems

See also

References