AVPlayerView.beginTrimming Question

I am using an AVPlayerView and I'm trying to call the beginTrimming method. However it isn't working (ie. not entering trimming mode), so I checked its .canBeginTrimming property and found that it is false.

The .mov files I am using are local and I'm accessing them via their urls. They load and play properly, I just can't enter trimming mode. (Also, if I open the same files in QuickTimePlayer I can trim them.)

The research I've found says: "This property value is false if the current controls style doesn’t support trimming, the media is content protected, or when playing HTTP Live Streaming media. The .mov files I am using are local and I'm accessing them via their urls. They load and play properly, I just can't enter trimming mode. (Also, if I open the same files in QuickTimePlayer I can trim them.)

I have an outlet to the AVPlayerView in my view controller. The control's style is set to default and "show buttons" is set to Frame Stepping.

Why might the player I have set up not allow trimming? Here is where I am loading the mov file, checking whether trimming is allowed and attempting to enter trimming mode:

    func tableViewSelectionDidChange(_ notification: Notification) {
        let row = movTableView.selectedRow
        guard row != -1 else { return }
        let selectedURL = movDict[allFilenames[row]]
        print(selectedURL)
        if let selectedURL {
            let player = AVPlayer(url: selectedURL)
            movPlayerView.player = player
            if movPlayerView.canBeginTrimming {
                print("medial player supports trimming")
            } else {
                print("media player does NOT support trimming")
            }
            movPlayerView.beginTrimming { result in
                if result == .okButton {
                    print("trimming ended. ok pressed")
                } else {
                    print("cancel pressed.")
                }
            }
        }
    }