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# Dictionary Keys

Keys to use when working with dictionary representations of a time range.

## Discussion

To convert a `CMTimeRange` to and from a `CFDictionary`, see [`CMTimeRangeCopyAsDictionary(_:allocator:)`](/documentation/CoreMedia/CMTimeRangeCopyAsDictionary(_:allocator:)) and [`CMTimeRangeMakeFromDictionary(_:)`](/documentation/CoreMedia/CMTimeRangeMakeFromDictionary(_:)).

## Topics

### Constants

[`let kCMTimeRangeStartKey: CFString`](/documentation/CoreMedia/kCMTimeRangeStartKey)

The key for the start field of a time range.

[`let kCMTimeRangeDurationKey: CFString`](/documentation/CoreMedia/kCMTimeRangeDurationKey)

The key for the timescale of a time range.


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