# Implementing Trimming in a macOS Player Provide a QuickTime media-trimming experience in your macOS app. ## Discussion You use [`AVPlayerView`](/documentation/AVKit/AVPlayerView) to provide a playback experience like that of QuickTime Player in macOS. However, `AVPlayerView` not only provides the QuickTime playback interface, but it also provides the QuickTime media-trimming experience.  ### Verify that Trimming Is Allowed Before attempting to put the player into trimming mode, verify that trimming is allowed by querying the player view’s [`canBeginTrimming`](/documentation/AVKit/AVPlayerView/canBeginTrimming) property. This property returns `false` if you’re playing an asset delivered over HTTP Live Streaming or if the asset is content protected. If you’re presenting a menu item to initiate trimming, a good place to perform this check is in the method of , so that the menu item can automatically be disabled if trimming is disallowed. ```swift override func validateUserInterfaceItem(_ item: NSValidatedUserInterfaceItem) -> Bool { if item.action == #selector(beginTrimming) { return playerView.canBeginTrimming } return super.validateUserInterfaceItem(item) } ``` ### Enter Trimming Mode After you’ve determined that the media supports trimming, you call the [`beginTrimming(completionHandler:)`](/documentation/AVKit/AVPlayerView/beginTrimming(completionHandler:)). This method takes a completion block that you use to determine whether the user completed the trim or canceled the operation. ```swift @IBAction func beginTrimming(_ sender: AnyObject) { playerView.beginTrimming { result in if result == .okButton { // user selected Trim button (AVPlayerViewTrimResult.okButton)... } else { // user selected Cancel button (AVPlayerViewTrimResult.cancelButton)... } } } ``` ### Transcode the Trimmed Asset Because is an immutable object, you may be wondering how its duration is changed when you click the Trim button. Trimming relies on a feature of to adjust the presented time range. `AVPlayerItem` provides the and properties that set the in and out points for a media item. It doesn’t change the underlying asset, but essentially changes your effective view of it. To save the results of the user’s trim operation, you export a new copy of the asset, trimming it to the specified times. The simplest way to do this is to use , which provides a simple and performant way for you to transcode the media of an asset. You create a new export session, passing it the asset to export along with a transcoding preset to use. ```swift // Transcoding preset let preset = AVAssetExportPresetAppleM4V720pHD let exportSession = AVAssetExportSession(asset: playerItem.asset, presetName: preset)! exportSession.outputFileType = AVFileTypeAppleM4V exportSession.outputURL = // Output URL ``` This example uses a preset to export the media as a 720p, M4V file, but `AVAssetExportSession` supports a wide variety of export presets. To find out what export session presets are supported for the current asset, you can use the session’s class method, passing it the asset you want to export. This method returns an array of valid presets that you can use in your export. ### Select the Trimmed Asset To export only the content the user trimmed, you use the current player item’s reverse and forward end-time values to define a to set on the export session. ```swift // Create CMTimeRange with the trim in/out point times let startTime = self.playerItem.reversePlaybackEndTime let endTime = self.playerItem.forwardPlaybackEndTime let timeRange = CMTimeRangeFromTimeToTime(startTime, endTime) exportSession.timeRange = timeRange ``` ### Export the Trimmed Asset To perform the actual export operation, you call its method. Check the status of the export session in the completion handler and handle completion and failure cases. ```swift exportSession.exportAsynchronously { switch exportSession.status { case .completed: // Export Complete case .failed: // failed default: // handle others } } ``` --- Copyright © 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)