Swift 3对我来说就像一个魅力！

Swift 3 Worked like a charm for me!

func exportVideoAsset(_ asset: PHAsset) {
    let filename = UUID().uuidString.appending(".mp4") // setting random file name

    let documentsUrl = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!

    do {
        var fileurl = try documentsUrl.absoluteString.appending(filename).asURL()
        print("exporting video to ", fileurl)
        fileurl = fileurl.standardizedFileURL


        let options = PHVideoRequestOptions()
        options.deliveryMode = .highQualityFormat
        options.isNetworkAccessAllowed = true

        // remove any existing file at that location
        do {
            try FileManager.default.removeItem(at: fileurl)
        }
        catch {
            // most likely, the file didn't exist.  Don't sweat it
        }

        PHImageManager.default().requestExportSession(forVideo: asset, options: options, exportPreset: AVAssetExportPresetHighestQuality) {
            (exportSession: AVAssetExportSession?, _) in

            if exportSession == nil {
                print("COULD NOT CREATE EXPORT SESSION")
                return
            }

            exportSession!.outputURL = fileurl
            exportSession!.outputFileType = AVFileTypeMPEG4 //file type encode goes here, you can change it for other types

            print("GOT EXPORT SESSION")
            exportSession!.exportAsynchronously() {
                 print("EXPORT DONE")
            }

            print("progress: \(exportSession!.progress)")
            print("error: \(exportSession!.error)")
            print("status: \(exportSession!.status.rawValue)")
        }
    }
    catch {
        // something may happend here, like no disk space
    }
}