private async Task TranscodeAsync(StorageFile source)
        {
            var destination = await ApplicationData.Current.LocalFolder.CreateFileAsync("temp.step2.mp4", CreationCollisionOption.ReplaceExisting);

            var encodingProfile = await MediaEncodingProfile.CreateFromFileAsync(source);

            var effect1 = await CreateEffectDefinitionAsync(encodingProfile.Video, 0);

            var transcoder = new MediaTranscoder();
            transcoder.AddVideoEffect(effect1.ActivatableClassId, true, effect1.Properties);

            var profile = MediaEncodingProfile.CreateMp4(VideoEncodingQuality.Vga);
            profile.Video.Width = 480;
            profile.Video.Height = 480;

            var prepare = await transcoder.PrepareFileTranscodeAsync(source, destination, profile);
            var transcode = prepare.TranscodeAsync();

            transcode.Progress += new AsyncActionProgressHandler<double>(TranscodeProgress);

            await transcode;
        }

        private async Task<IVideoEffectDefinition> CreateEffectDefinitionAsync(VideoEncodingProperties props, int index)
        {
            var file = await StorageFile.GetFileFromApplicationUriAsync(new Uri("ms-appx:///Assets/croppedmark.png"));
            var stream = await file.OpenReadAsync();
            var bd = await BitmapDecoder.CreateAsync(stream);
            var pd = await bd.GetPixelDataAsync();
            var tempBuffer = pd.DetachPixelData();
            var definition1 = new WatermarkEffectDefinition(tempBuffer.AsBuffer());
            definition1.InputHeight = 640;
            definition1.InputWidth = 480;
            definition1.OutputHeight = 480;
            definition1.OutputWidth = 480;
            return definition1;
        }