<!--
{
  "availability" : [
    "iOS: 15.0.0 -",
    "iPadOS: 15.0.0 -",
    "macCatalyst: 15.0.0 -",
    "macOS: 12.0.0 -",
    "tvOS: 15.0.0 -",
    "visionOS: 1.0.0 -",
    "watchOS: 8.0.0 -"
  ],
  "documentType" : "symbol",
  "framework" : "AVFoundation",
  "identifier" : "/documentation/AVFoundation/AVPlayer/sourceClock",
  "metadataVersion" : "0.1.0",
  "role" : "Instance Property",
  "symbol" : {
    "kind" : "Instance Property",
    "modules" : [
      "AVFoundation"
    ],
    "preciseIdentifier" : "c:objc(cs)AVPlayer(py)sourceClock"
  },
  "title" : "sourceClock"
}
-->

# sourceClock

A clock the player uses for item time bases.

```
nonisolated var sourceClock: CMClock? { get set }
```

## Discussion

The default value is `nil`. Setting an explicit source clock is useful to synchronize video-only movies with audio that plays through a different audio device.

> Important:
> Specifying a source clock for a device other than the one playing audio may cause audio to drift out of sync.

---

Copyright &copy; 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)