Swift 動画撮影をlandscape(横向き)で

#AVCaptureMovieFileOutputの設定
まず，　ファイル出力の設定時点で，向きを変更可能にします。(デフォルトは変更不可)

captureSession.addOutput(videoFileOutput)
let videoDataOuputConnection = videoFileOutput.connection(with: .video)
videoFileOutput.setRecordsVideoOrientationAndMirroringChangesAsMetadataTrack(true, for: videoDataOuputConnection!)

録画開始時にファイル出力の向きをデバイスの向きに合わせます。

let videoDataOuputConnection = videoFileOutput.connection(with: .video)
let orientation = UIDevice.current.orientation
videoDataOuputConnection!.videoOrientation = AVCaptureVideoOrientation(rawValue: orientation.rawValue)!

参考：
How to record landscape video in a portrait application? (Swift 2, iPhone)

#表示映像の設定

回転した際に向きを取得します。

override func viewWillTransitionToSize(size: CGSize, withTransitionCoordinator coordinator: UIViewControllerTransitionCoordinator) {
    super.viewWillTransitionToSize(size, withTransitionCoordinator: coordinator)

    coordinator.animateAlongsideTransition(
        nil,
        completion: {(UIViewControllerTransitionCoordinatorContext) in
            //画面の回転後に向きを教える。
            if let orientation = self.convertUIOrientation2VideoOrientation({return UIApplication.sharedApplication().statusBarOrientation}) {
                videoPreviewLayer?.connection.videoOrientation = orientation
            }
        }
    )
}


func convertUIOrientation2VideoOrientation(f: () -> UIInterfaceOrientation) -> AVCaptureVideoOrientation? {
    let v = f()
    switch v {
        case UIInterfaceOrientation.Unknown:
            return nil
        default:
            return ([
                UIInterfaceOrientation.Portrait: AVCaptureVideoOrientation.Portrait,
                UIInterfaceOrientation.PortraitUpsideDown: AVCaptureVideoOrientation.PortraitUpsideDown,
                UIInterfaceOrientation.LandscapeLeft: AVCaptureVideoOrientation.LandscapeLeft,
                UIInterfaceOrientation.LandscapeRight: AVCaptureVideoOrientation.LandscapeRight
            ])[v]
    }
}

参考：
Swift - iOSでビデオカメラを使用時、端末の向きに対応