How to do Slow Motion video in IOS

Question

I have to do \"slow motion\" in a video file along with audio, in-between some frames and need to store the ramped video as a new video.

Answer 1

An example in swift :

I

var asset: AVAsset?  
func configureAssets(){

    let videoAsset = AVURLAsset(url: Bundle.main.url(forResource: "sample", withExtension: "m4v")!)
    let audioAsset = AVURLAsset(url: Bundle.main.url(forResource: "sample", withExtension: "m4a")!)
    //    let audioAsset2 = AVURLAsset(url: Bundle.main.url(forResource: "audio2", withExtension: "m4a")!)

    let comp = AVMutableComposition()

    let videoAssetSourceTrack = videoAsset.tracks(withMediaType: AVMediaTypeVideo).first! as AVAssetTrack
    let audioAssetSourceTrack = videoAsset.tracks(withMediaType: AVMediaTypeAudio).first! as AVAssetTrack
    //    let audioAssetSourceTrack2 = audioAsset2.tracks(withMediaType: AVMediaTypeAudio).first! as AVAssetTrack

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

    do {

        try videoCompositionTrack.insertTimeRange(
            CMTimeRangeMake(kCMTimeZero, CMTimeMakeWithSeconds(9 , 600)),
            of: videoAssetSourceTrack,
            at: kCMTimeZero)



        try audioCompositionTrack.insertTimeRange(
            CMTimeRangeMake(kCMTimeZero, CMTimeMakeWithSeconds(9, 600)),
            of: audioAssetSourceTrack,
            at: kCMTimeZero)

        //
        //      try audioCompositionTrack.insertTimeRange(
        //        CMTimeRangeMake(kCMTimeZero, CMTimeMakeWithSeconds(3, 600)),
        //        of: audioAssetSourceTrack2,
        //        at: CMTimeMakeWithSeconds(7, 600))

        let videoScaleFactor = Int64(2.0)
        let videoDuration: CMTime = videoAsset.duration


        videoCompositionTrack.scaleTimeRange(CMTimeRangeMake(kCMTimeZero, videoDuration), toDuration: CMTimeMake(videoDuration.value * videoScaleFactor, videoDuration.timescale))
        audioCompositionTrack.scaleTimeRange(CMTimeRangeMake(kCMTimeZero, videoDuration), toDuration: CMTimeMake(videoDuration.value * videoScaleFactor, videoDuration.timescale))
        videoCompositionTrack.preferredTransform = videoAssetSourceTrack.preferredTransform



    }catch { print(error) }

    asset = comp
}

II

  func createFileFromAsset(_ 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: AVAssetExportPresetLowQuality){


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

 }

 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).")
}
}