将背景颜色添加到MediaComposition

Question

我正在尝试创建一个MediaComposition.我成功地将多个png图像组合成一个视频; 但是,创建的文件具有黑色背景.起初我认为这可能是因为文件是png文件,但jpgs也会出现相同的bevaviour.以下是我如何保存图像:

public async Task<bool> Save(InkCanvas canvas, StorageFile file)
{

    if (canvas != null && canvas.InkPresenter.StrokeContainer.GetStrokes().Count > 0)
    {
        if (file != null)
        {
            using (IRandomAccessStream stream = await file.OpenAsync(FileAccessMode.ReadWrite))
            {
                await canvas.InkPresenter.StrokeContainer.SaveAsync(stream);
            }
        }
        Clear(canvas);
        return true;
    }
    return false;
}

它可以保存图像,但背景是alpha.这意味着当我尝试将这些链接到一个媒体合成中时,没有背景,它呈现为黑色.我在创建MediaComposition时尝试使用叠加来纠正这个问题:

MediaClip overlayVideoClip = MediaClip.CreateFromColor(Colors.White, new TimeSpan(0, 1, 0));
MediaOverlay mo = new MediaOverlay(overlayVideoClip);
MediaOverlayLayer mol = new MediaOverlayLayer();
mol.Overlays.Add(mo);

composition.OverlayLayers.Add(mol);

但无济于事.我怀疑在这种情况下我误解了覆盖一词的含义.所以,我的问题是:是否可以在合成时叠加视频,如果是,如何？或者,如果需要在图像本身中完成,如何使用背景保存图像？

编辑:

我已经取得了进步(？); 以下编译并运行,但创建一个纯黑色图像:

    public async Task TestSave(InkCanvas canvas, StorageFile file)
    {
        RenderTargetBitmap rtb = 
           new RenderTargetBitmap();
        PixelFormats.Pbgra32);
        await rtb.RenderAsync(canvas);
        var pixelBuffer = await rtb.GetPixelsAsync();

        using (IRandomAccessStream stream = 
             await file.OpenAsync(FileAccessMode.ReadWrite))
        {                
            BitmapEncoder encoder = 
                 await BitmapEncoder.CreateAsync(BitmapEncoder.PngEncoderId, stream);

            encoder.SetPixelData(BitmapPixelFormat.Bgra8,
                BitmapAlphaMode.Straight,
                (uint)rtb.PixelWidth,
                (uint)rtb.PixelHeight,
                96d, 96d,
                pixelBuffer.ToArray());

            await encoder.FlushAsync();                
        }
    }

编辑:

我找到了这个答案,通过使用Win2D库解决了这个问题; 虽然它没有解决我的实际问题,但它让我可以解决它.希望有更好的解决方案.

Answer 1

我唯一理解的是你试图用背景保存图像.我解决这个问题的建议是将透明图像保存为类似的东西

<StackPanel x:Name="AreaWhichWillBeSavedToImage" Background=*Some Color*>
  <Image x:Name="theAlphaImage">
</StackPanel>

现在,如果您不希望图像显示在GUI上,只需将其设置为隐藏.

然后,您可以使用您选择的颜色背景保存文件.

var bitmap = await SaveToFileAsync(AreaWhichWillBeSavedToImage, await StorageFile.GetFileFromPathAsync(Windows.ApplicationModel.Package.Current.InstalledLocation.Path + @"someimage.jpg"));

  async Task<RenderTargetBitmap> SaveToFileAsync(FrameworkElement uielement, StorageFile file)
    {
        if (file != null)
        {
            CachedFileManager.DeferUpdates(file);

            Guid encoderId = GetBitmapEncoder(file.FileType);

            try
            {
                using (var stream = await file.OpenAsync(FileAccessMode.ReadWrite))
                {
                    return await CaptureToStreamAsync(uielement, stream, encoderId);
                }
            }
            catch (Exception ex)
            {
                //DisplayMessage(ex.Message);
            }

            var status = await CachedFileManager.CompleteUpdatesAsync(file);
        }

        return null;
    }

    async Task<RenderTargetBitmap> CaptureToStreamAsync(FrameworkElement uielement, IRandomAccessStream stream, Guid encoderId)
    {
        try
        {
            var renderTargetBitmap = new RenderTargetBitmap();
            await renderTargetBitmap.RenderAsync(uielement);

            var pixels = await renderTargetBitmap.GetPixelsAsync();

            var logicalDpi = DisplayInformation.GetForCurrentView().LogicalDpi;
            var encoder = await BitmapEncoder.CreateAsync(encoderId, stream);
            encoder.SetPixelData(
                BitmapPixelFormat.Bgra8,
                BitmapAlphaMode.Ignore,
                (uint)renderTargetBitmap.PixelWidth,
                (uint)renderTargetBitmap.PixelHeight,
                logicalDpi,
                logicalDpi,
                pixels.ToArray());

            await encoder.FlushAsync();

            return renderTargetBitmap;
        }
        catch (Exception ex)
        {
            //DisplayMessage(ex.Message);
        }

        return null;
    }

    Guid GetBitmapEncoder(string fileType)
    {
        Guid encoderId = BitmapEncoder.JpegEncoderId;
        switch (fileType)
        {
            case ".bmp":
                encoderId = BitmapEncoder.BmpEncoderId;
                break;
            case ".gif":
                encoderId = BitmapEncoder.GifEncoderId;
                break;
            case ".png":
                encoderId = BitmapEncoder.PngEncoderId;
                break;
            case ".tif":
                encoderId = BitmapEncoder.TiffEncoderId;
                break;
        }

        return encoderId;
    }