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 Manager ...

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 for which a central processing unit (CPU) was used for processing instructions of a computer program or operating system, as opposed to elapsed time, which includes for example, waiting for input ...

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 way for two or more computer programs to communicate with each other. It is a type of software Interface (computing), interface, offering a service to other pieces of software. A document or standa ...

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, which was released five years before, at the time being the longest time span between successive releases of ...

, including

Windows Media Player Windows Media Player (WMP) is the first media player and media library application that was developed by Microsoft for playing audio, video and viewing images on personal computers running the Microsoft Windows operating system, as well as on ...

and

Windows Media Center Windows Media Center (WMC) is a defunct 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 Ultimate e ...

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