import UIKit
import AVFoundation

class ViewController: UIViewController {

  var asset: AVAsset?

  @IBAction func exportBtnDidTap(_ sender: AnyObject) {

    guard let asset = asset else {
      return
    }

    createAudioFileFromAsset(asset)
  }


  override func viewDidLoad() {
    super.viewDidLoad()

    let videoAsset = AVURLAsset(url: Bundle.main.url(forResource: "sample", withExtension: "m4v")!)

    let comp = AVMutableComposition()

    let videoAssetSourceTrack = videoAsset.tracks(withMediaType: AVMediaTypeVideo).first! as AVAssetTrack


    let videoCompositionTrack = comp.addMutableTrack(withMediaType: AVMediaTypeVideo, preferredTrackID: kCMPersistentTrackID_Invalid)

    do {

        try videoCompositionTrack.insertTimeRange(
            CMTimeRangeMake(kCMTimeZero, CMTimeMakeWithSeconds(1, 600)),
            of: videoAssetSourceTrack,
            at: kCMTimeZero)

    }catch { print(error) }

    asset = comp
    }















  func deleteFile(_ filePath:URL) {
    guard FileManager.default.fileExists(atPath: filePath.path) else {
      return
    }

    do {
      try FileManager.default.removeItem(atPath: filePath.path)
    }catch{
      fatalError("Unable to delete file: \(error) : \(#function).")
    }
  }











  func createAudioFileFromAsset(_ asset: AVAsset){

    let documentsDirectory = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)[0] as URL

    let filePath = documentsDirectory.appendingPathComponent("rendered-audio.m4v")
    deleteFile(filePath)

    if let exportSession = AVAssetExportSession(asset: asset, presetName: AVAssetExportPreset640x480){

      exportSession.canPerformMultiplePassesOverSourceMediaData = true
      exportSession.outputURL = filePath
      exportSession.timeRange = CMTimeRangeMake(kCMTimeZero, asset.duration)
      exportSession.outputFileType = AVFileTypeQuickTimeMovie
      exportSession.exportAsynchronously {
        _ in
        print("finished: \(filePath) :  \(exportSession.status.rawValue) ")
      }
    }

    }
}