BitmapEncoder Save Not Supported

Question

I have the following code and I can't see anything wrong, any ideas on what the problem could be?

private static string SaveBaseImage( ZipArchive arc, DBImage image, int imageIndex )
{
    using (var mem = new MemoryStream(image.Data))
    {
        var bmp = BitmapFrame.Create(mem);
        //var bmp = BitmapFrame.Create(m‌​em, BitmapCreateOptions.‌​None, BitmapCacheOption.On‌​Load);
        var codex = bmp.Decoder.CodecInfo;

        var filename = $"{imageIndex}{codex.FileExtensions}";
        var imagezip = arc.CreateEntry(filename,CompressionLevel.Optimal));
        using (var imagestream = imagezip.Open())
        {
            SaveImage( bmp, imagestream);
        }
        return filename;
    }
}

private static void SaveImage(BitmapFrame data, Stream saveStream)
{
    var codex = data.Decoder.CodecInfo;
    var encoder = BitmapEncoder.Create(codex.ContainerFormat);
    encoder.Frames.Add(data);
    encoder.Save(saveStream);
}

when I run it throws

System.NotSupportedException occurred HResult=-2146233067

Message=Specified method is not supported. Source=PresentationCore

StackTrace: at System.Windows.Media.Imaging.BitmapEncoder.Save(Stream stream) at FileFormatters.Export.SaveImage(BitmapFrame data, Stream saveStream)

InnerException: null

The MSDN page says

NotSupportedException :The Frames value that is passed to the encoder is null.

NotSupportedException :The Frames count is less than or equal to zero.

However frames count is 1 and data is not null

further info

arc declared as using (ZipArchive arc = new ZipArchive(stream, ZipArchiveMode.Create))
image.Data is byte[]
codex.FriendlyName = "PNG Decoder"
encoder.CodecInfo.FriendlyName = "PNG Encoder"

Answer 1

It seems to be necessary to write the image buffer to an intermediate MemoryStream, before it can be written to a ZipEntry Stream:

private static void SaveImage(BitmapFrame data, Stream saveStream)
{
    var encoder = BitmapEncoder.Create(data.Decoder.CodecInfo.ContainerFormat);
    encoder.Frames.Add(data);

    using (var memoryStream = new MemoryStream())
    {
        encoder.Save(memoryStream);
        memoryStream.Position = 0;
        memoryStream.CopyTo(saveStream);
    }
}