how to trim a video in swift for a particular time

A swift4 version for this.

static func cropVideo(sourceURL: URL, startTime: Double, endTime: Double, completion: ((_ outputUrl: URL) -> Void)? = nil)
{
    let fileManager = FileManager.default
    let documentDirectory = fileManager.urls(for: .documentDirectory, in: .userDomainMask)[0]

    let asset = AVAsset(url: sourceURL)
    let length = Float(asset.duration.value) / Float(asset.duration.timescale)
    print("video length: \(length) seconds")

    var outputURL = documentDirectory.appendingPathComponent("output")
    do {
        try fileManager.createDirectory(at: outputURL, withIntermediateDirectories: true, attributes: nil)
        outputURL = outputURL.appendingPathComponent("\(sourceURL.lastPathComponent).mp4")
    }catch let error {
        print(error)
    }

    //Remove existing file
    try? fileManager.removeItem(at: outputURL)

    guard let exportSession = AVAssetExportSession(asset: asset, presetName: AVAssetExportPresetHighestQuality) else { return }
    exportSession.outputURL = outputURL
    exportSession.outputFileType = .mp4

    let timeRange = CMTimeRange(start: CMTime(seconds: startTime, preferredTimescale: 1000),
                                end: CMTime(seconds: endTime, preferredTimescale: 1000))

    exportSession.timeRange = timeRange
    exportSession.exportAsynchronously {
        switch exportSession.status {
        case .completed:
            print("exported at \(outputURL)")
            completion?(outputURL)
        case .failed:
            print("failed \(exportSession.error.debugDescription)")
        case .cancelled:
            print("cancelled \(exportSession.error.debugDescription)")
        default: break
        }
    }
}

This one does the job and it fixes the rotation problem.

extension AVAsset {
    func assetByTrimming(startTime: CMTime, endTime: CMTime) throws -> AVAsset {
        let duration = CMTimeSubtract(endTime, startTime)
        let timeRange = CMTimeRange(start: startTime, duration: duration)

        let composition = AVMutableComposition()

        do {
            for track in tracks {
                let compositionTrack = composition.addMutableTrack(withMediaType: track.mediaType, preferredTrackID: track.trackID)
                compositionTrack?.preferredTransform = track.preferredTransform
                try compositionTrack?.insertTimeRange(timeRange, of: track, at: CMTime.zero)
            }
        } catch let error {
            throw TrimError("error during composition", underlyingError: error)
        }

        return composition
    }

struct TrimError: Error {
    let description: String
    let underlyingError: Error?

    init(_ description: String, underlyingError: Error? = nil) {
        self.description = "TrimVideo: " + description
        self.underlyingError = underlyingError
    }
}

func cropVideo1(_ sourceURL1: URL, statTime:Float, endTime:Float){
        let videoAsset: AVAsset = AVAsset(url: sourceURL1) as AVAsset
        let composition = AVMutableComposition()
        composition.addMutableTrack(withMediaType: AVMediaTypeVideo, preferredTrackID: CMPersistentTrackID())

        let videoComposition = AVMutableVideoComposition()
        videoComposition.renderSize = CGSize(width: 1280, height: 768)
        videoComposition.frameDuration = CMTimeMake(8, 15)

        let instruction = AVMutableVideoCompositionInstruction()
        let length = Float(videoAsset.duration.value)
        print(length)

        instruction.timeRange = CMTimeRangeMake(kCMTimeZero, CMTimeMakeWithSeconds(60, 30))

        let start = statTime
        let end = endTime

        let exportSession = AVAssetExportSession(asset: videoAsset, presetName: AVAssetExportPresetHighestQuality)!
        exportSession.outputFileType = AVFileTypeMPEG4

        let startTime = CMTime(seconds: Double(start ), preferredTimescale: 1000)
        let endTime = CMTime(seconds: Double(end ), preferredTimescale: 1000)
        let timeRange = CMTimeRange(start: startTime, end: endTime)

        exportSession.timeRange = timeRange

        let formatter = DateFormatter()
        formatter.dateFormat = "yyyy'-'MM'-'dd'T'HH':'mm':'ss'Z'"

        let date = Date()

        let documentsPath = NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true)[0] as NSString
        let outputPath = "\(documentsPath)/\(formatter.string(from: date)).mp4"
        let outputURL = URL(fileURLWithPath: outputPath)

        exportSession.outputURL = outputURL
        exportSession.outputFileType = AVFileTypeQuickTimeMovie
        print("sucess")
        exportSession.exportAsynchronously(completionHandler: { () -> Void in
            DispatchQueue.main.async(execute: {
                self.exportDidFinish(exportSession)
                print("sucess")


            })
        })
    }
    func exportDidFinish(_ session: AVAssetExportSession) {

        if session.status == AVAssetExportSessionStatus.completed {
            let outputURL = session.outputURL
            let library = ALAssetsLibrary()
            if library.videoAtPathIs(compatibleWithSavedPhotosAlbum: outputURL) {
                library.writeVideoAtPath(toSavedPhotosAlbum: outputURL) { alAssetURL, error in
                    if error != nil {
                        DispatchQueue.main.async(execute: {
                            print("Failed to save video")
                        })
                    } else {
                        DispatchQueue.main.async(execute: {
                            Print("Sucessfully saved Video")
                        })
                    }
                    self.activityIndicator.stopAnimating()
                }
            }
        }
    }

I found my solution using this method and it works like a charm....

func cropVideo(sourceURL1: NSURL, statTime:Float, endTime:Float)
{
    let manager = NSFileManager.defaultManager()
    
    guard let documentDirectory = try? manager.URLForDirectory(.DocumentDirectory, inDomain: .UserDomainMask, appropriateForURL: nil, create: true) else {return}
    guard let mediaType = "mp4" as? String else {return}
    guard let url = sourceURL1 as? NSURL else {return}
    
    if mediaType == kUTTypeMovie as String || mediaType == "mp4" as String {
        let asset = AVAsset(URL: url)
        let length = Float(asset.duration.value) / Float(asset.duration.timescale)
        print("video length: \(length) seconds")
        
        let start = statTime
        let end = endTime
        
        var outputURL = documentDirectory.URLByAppendingPathComponent("output")
        do {
            try manager.createDirectoryAtURL(outputURL, withIntermediateDirectories: true, attributes: nil)
            let name = Moment.newName()
            outputURL = outputURL.URLByAppendingPathComponent("\(name).mp4")
        }catch let error {
            print(error)
        }
        
        //Remove existing file
        _ = try? manager.removeItemAtURL(outputURL)
        
        
        guard let exportSession = AVAssetExportSession(asset: asset, presetName: AVAssetExportPresetHighestQuality) else {return}
        exportSession.outputURL = outputURL
        exportSession.outputFileType = AVFileTypeMPEG4
        
        let startTime = CMTime(seconds: Double(start ?? 0), preferredTimescale: 1000)
        let endTime = CMTime(seconds: Double(end ?? length), preferredTimescale: 1000)
        let timeRange = CMTimeRange(start: startTime, end: endTime)
        
        exportSession.timeRange = timeRange
        exportSession.exportAsynchronouslyWithCompletionHandler{
            switch exportSession.status {
            case .Completed:
                print("exported at \(outputURL)")
               self.saveVideoTimeline(outputURL)
            case .Failed:
                print("failed \(exportSession.error)")
                
            case .Cancelled:
                print("cancelled \(exportSession.error)")
                
            default: break
            }
        }
    }
}

Swift 5

    func cropVideo(sourceURL1: URL, statTime:Float, endTime:Float)
{
    let manager = FileManager.default

    guard let documentDirectory = try? manager.url(for: .documentDirectory, in: .userDomainMask, appropriateFor: nil, create: true) else {return}
    let mediaType = "mp4"
    if mediaType == kUTTypeMovie as String || mediaType == "mp4" as String {
        let asset = AVAsset(url: sourceURL1 as URL)
        let length = Float(asset.duration.value) / Float(asset.duration.timescale)
        print("video length: \(length) seconds")

        let start = statTime
        let end = endTime

        var outputURL = documentDirectory.appendingPathComponent("output")
        do {
            try manager.createDirectory(at: outputURL, withIntermediateDirectories: true, attributes: nil)
            outputURL = outputURL.appendingPathComponent("\(UUID().uuidString).\(mediaType)")
        }catch let error {
            print(error)
        }

        //Remove existing file
        _ = try? manager.removeItem(at: outputURL)


        guard let exportSession = AVAssetExportSession(asset: asset, presetName: AVAssetExportPresetHighestQuality) else {return}
        exportSession.outputURL = outputURL
        exportSession.outputFileType = .mp4

        let startTime = CMTime(seconds: Double(start ), preferredTimescale: 1000)
        let endTime = CMTime(seconds: Double(end ), preferredTimescale: 1000)
        let timeRange = CMTimeRange(start: startTime, end: endTime)

        exportSession.timeRange = timeRange
        exportSession.exportAsynchronously{
            switch exportSession.status {
            case .completed:
                print("exported at \(outputURL)")
            case .failed:
                print("failed \(exportSession.error)")

            case .cancelled:
                print("cancelled \(exportSession.error)")

            default: break
            }
        }
    }
}