public class TrimVideo : ITrim
    {
        AVAsset avAsset;

        public void Trim(int start, int end, string path)
        {
            avAsset = AVAsset.FromUrl(NSUrl.FromFilename(path));

            if (avAsset.Duration.Seconds < 60)
            {
                return;
            }

            string preset = getPreset(avAsset);

            var exportSession = new AVAssetExportSession(avAsset, preset);

            // куда сохранится видео
            exportSession.OutputUrl = NSUrl.FromFilename(outputTrim());
            // формат видео
            exportSession.OutputFileType = AVFileType.Mpeg4;

            var range = new CMTimeRange();
            range.Start = CMTime.FromSeconds(start, avAsset.Duration.TimeScale);
            range.Duration = CMTime.FromSeconds(end, avAsset.Duration.TimeScale);
            exportSession.TimeRange = range;

            exportSession.ExportAsynchronously(delegate {
                switch (exportSession.Status)
                {
                    case AVAssetExportSessionStatus.Completed:
                        Console.WriteLine($"exported at {exportSession.OutputUrl}");
                        Device.BeginInvokeOnMainThread(() =>
                            UIVideo.SaveToPhotosAlbum(exportSession.OutputUrl.Path, delegate (string _path, NSError error)
                            {
                                Console.WriteLine($"path {_path}");
                                if (error != null)
                                    Console.WriteLine($"error {error.Description}");

                            }));
                        break;
                    case AVAssetExportSessionStatus.Failed:
                        Console.WriteLine($"failed {exportSession.Error}");
                        break;
                    case AVAssetExportSessionStatus.Cancelled:
                        Console.WriteLine($"cancelled {exportSession.Error}");
                        break;
                    default:
                        Console.WriteLine($"def {exportSession.Error}");
                        break;
                }
            });
        }

        string outputTrim()
        {
            var documents = NSFileManager.DefaultManager.GetUrls(NSSearchPathDirectory.DocumentDirectory, NSSearchPathDomain.User)[0].Path;
            return Path.Combine(documents, $"trimmed{Guid.NewGuid()}.mp4");
        }

        string getPreset(AVAsset asset)
        {
            var compatiblePresets = AVAssetExportSession.ExportPresetsCompatibleWithAsset(avAsset).ToList();
            string preset;

            if (compatiblePresets.Contains("AVAssetExportPresetLowQuality"))
            {
                preset = "AVAssetExportPresetLowQuality";
            }
            else
            {
                preset = compatiblePresets.FirstOrDefault();
            }

            return preset;
        }
    }