UIImagePickerControllerで取得した動画（MOV）をMP4に変換

やりたいこと

カメラロールにある動画ファイルをトリムして取得したいのだが、MOV形式になってしまう。
MP4で取り込みたいので、トリム後に変換をするようにする。

import UIKit
import MobileCoreServices
import AVFoundation

class ViewController: UIViewController, UIImagePickerControllerDelegate, UINavigationControllerDelegate {

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }


    @IBAction func pushedButton(_ sender: AnyObject) {
        // カメラロールを表示
        if UIImagePickerController.isSourceTypeAvailable(UIImagePickerControllerSourceType.photoLibrary) {
            let controller = UIImagePickerController()
            controller.sourceType = UIImagePickerControllerSourceType.photoLibrary
            controller.mediaTypes=[kUTTypeMovie as String] // 動画のみ
            controller.delegate = self
            controller.allowsEditing = true
            controller.videoMaximumDuration = 5 // ５秒で動画を切り取る
            controller.videoQuality = UIImagePickerControllerQualityType.typeHigh // カメラのハイクォリティのサイズで取得する

            self.present(controller, animated: true, completion: nil)
        }
    }

    func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [String : Any]) {
        if let url = info[UIImagePickerControllerMediaURL] as? NSURL {
            // 一時保持用のパス
            let documentsPath = NSSearchPathForDirectoriesInDomains(.documentationDirectory, .userDomainMask, true)[0] as String
            let fileName = "tmpVideo.mp4"
            let videoPath = documentsPath + fileName
            let out: NSURL = NSURL.fileURL(withPath: videoPath) as NSURL

            // MOV→MP4に変換
            self.converVideo(inputURL: url, outputURL: out, handler: { (exportSession: AVAssetExportSession) in
                if (exportSession.status == AVAssetExportSessionStatus.completed) {
                    // カメラロールに保存する
                    UISaveVideoAtPathToSavedPhotosAlbum(out.path!, self, nil, nil)
                }
            })
        }
        picker.dismiss(animated: true, completion: nil)
    }

    func imagePickerControllerDidCancel(_ picker: UIImagePickerController) {
        picker.dismiss(animated: true, completion: nil)
    }

    func converVideo(inputURL: NSURL, outputURL: NSURL, handler: @escaping (_ exportSession: AVAssetExportSession) -> Void) {
        do {
            // ファイルがあれば削除
            try FileManager.default.removeItem(at: outputURL.absoluteURL!)
        }
        catch _ {

        }
        let asset:AVURLAsset = AVURLAsset.init(url: inputURL.absoluteURL!, options: nil)
        let exportSession:AVAssetExportSession = AVAssetExportSession.init(asset: asset, presetName: AVAssetExportPresetPassthrough)!
        exportSession.outputURL = outputURL.absoluteURL;
        exportSession.outputFileType = AVFileTypeMPEG4;     // MP4形式出力
        exportSession.exportAsynchronously(completionHandler: {() -> Void in
            handler(exportSession);
        })
    }
}