---
title: CMClock
framework: coremedia
role: collectionGroup
role_heading: API Collection
path: coremedia/cmclock-api
---

# CMClock

A reference clock you use to synchronize applications and devices.

## Overview

Overview The CMSync API provides a reference clock that you use to synchronize applications and devices. This API also provides functions to monitor relative drift between CMClocks and functions that are associated with timer services.

## Topics

### Accessing the Host Clock

- [CMClockGetHostTimeClock()](coremedia/cmclockgethosttimeclock().md)

### Stopping the Clock

- [CMClockInvalidate(_:)](coremedia/cmclockinvalidate(_:).md)

### Accessing and Converting Time

- [CMClockGetTime(_:)](coremedia/cmclockgettime(_:).md)
- [CMClockGetAnchorTime(_:clockTimeOut:referenceClockTimeOut:)](coremedia/cmclockgetanchortime(_:clocktimeout:referenceclocktimeout:).md)
- [CMClockConvertHostTimeToSystemUnits(_:)](coremedia/cmclockconverthosttimetosystemunits(_:).md)
- [CMClockMakeHostTimeFromSystemUnits(_:)](coremedia/cmclockmakehosttimefromsystemunits(_:).md)

### Getting and Syncing Time

- [CMSyncGetTime(_:)](coremedia/cmsyncgettime(_:).md)
- [CMSyncGetRelativeRate(_:relativeTo:)](coremedia/cmsyncgetrelativerate(_:relativeto:).md)
- [CMSyncGetRelativeRateAndAnchorTime(_:relativeTo:relativeRateOut:anchorTimeOut:relativeToAnchorTimeOut:)](coremedia/cmsyncgetrelativerateandanchortime(_:relativeto:relativerateout:anchortimeout:relativetoanchortimeout:).md)
- [CMSyncConvertTime(_:from:to:)](coremedia/cmsyncconverttime(_:from:to:).md)

### Determining Clock Drift

- [CMClockMightDrift(_:otherClock:)](coremedia/cmclockmightdrift(_:otherclock:).md)
- [CMSyncMightDrift(_:_:)](coremedia/cmsyncmightdrift(_:_:).md)

### Data Types

- [CMClock](coremedia/cmclock.md)
- [CMClockOrTimebase](coremedia/cmclockortimebase.md)
- [CMClockGetTypeID()](coremedia/cmclockgettypeid().md)

### Constants

- [CMClock Error Codes](coremedia/cmclock-error-codes.md)
- [CMTimebase Error Codes](coremedia/cmtimebase-errors.md)
- [CMSync error codes](coremedia/cmsync-error-codes.md)
- [Timebase Notifications](coremedia/timebase-notifications.md)

## See Also

### Media Synchronization

- [CMAudioClock](coremedia/cmaudioclock-api.md)
- [CMTimebase](coremedia/cmtimebase-api.md)