WPF Advanced Image

using System;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Media.Imaging;

namespace WpfApplication1 {

    public static class BitmapMetadataExtension {
        public static object GetQueryOrNull(this BitmapMetadata metadata, string query) {
            return metadata.ContainsQuery(query) ? metadata.GetQuery(query) : null;
        }
    }

    public class AdvancedImage : Image {

        new private static readonly DependencyProperty SourceProperty = DependencyProperty.Register("Source", typeof(ImageSource), typeof(AdvancedImage), new UIPropertyMetadata(null, new PropertyChangedCallback(SourceChanged)));

        new public ImageSource Source {
            get { return (ImageSource)GetValue(SourceProperty); }
            set { SetValue(SourceProperty, value); }
        }

        private static void SourceChanged(DependencyObject obj, DependencyPropertyChangedEventArgs ev) {
            ((AdvancedImage)obj).SourceChanged(ev);
        }

        private void SourceChanged(DependencyPropertyChangedEventArgs ev) {
            string oldValue = ev.OldValue == null ? null : ev.OldValue.ToString();
            string newValue = ev.NewValue == null ? null : ev.NewValue.ToString();
            if (oldValue == newValue) return;
            base.Source = Source;
            BeginAnimation(Image.SourceProperty, null);
            GifBitmapDecoder decoder = GetDecoder(Source) as GifBitmapDecoder;
            if (decoder == null || decoder.Frames.Count <= 1) return;
            ObjectAnimationUsingKeyFrames animation = new ObjectAnimationUsingKeyFrames();
            animation.Duration = TimeSpan.Zero;
            animation.RepeatBehavior = GetRepeatBehavior(decoder);
            GifFrame frame = new GifFrame(Source);
            foreach (BitmapFrame rawFrame in decoder.Frames) {
                frame = new GifFrame(rawFrame, frame);
                animation.KeyFrames.Add(new DiscreteObjectKeyFrame(frame.Bitmap, animation.Duration.TimeSpan));
                animation.Duration += frame.Delay;
            }
            BeginAnimation(Image.SourceProperty, animation);
        }

        private BitmapDecoder GetDecoder(ImageSource source) {
        try {
                if (source is BitmapImage) {
                    BitmapImage bmp = (BitmapImage)source;
                    if (bmp.UriSource != null) {
                        Uri uri = bmp.UriSource;
                        if (bmp.BaseUri != null && !uri.IsAbsoluteUri)
                            uri = new Uri(bmp.BaseUri, uri);
                        return BitmapDecoder.Create(uri, bmp.CreateOptions, bmp.CacheOption);
                    } else if (bmp.StreamSource != null)
                        return BitmapDecoder.Create(bmp.StreamSource, bmp.CreateOptions, bmp.CacheOption);
                } else if (source is BitmapFrame)
                    return ((BitmapFrame)source).Decoder;
        } catch {}
            return null;
        }

        private RepeatBehavior GetRepeatBehavior(GifBitmapDecoder decoder) {
            BitmapMetadata metadata = decoder.Metadata as BitmapMetadata;
            if (metadata != null) {
                byte[] application = metadata.GetQueryOrNull("/appext/Application") as byte[];
                if (application != null && Encoding.Default.GetString(application) == "NETSCAPE2.0") {
                    byte[] data = metadata.GetQueryOrNull("/appext/Data") as byte[];
                    if (data != null && data.Length >= 4) {
                        int count = BitConverter.ToUInt16(data, 2);
                        if (count != 0) return new RepeatBehavior(count);
                    }
                } else return new RepeatBehavior(1);
            }
            return RepeatBehavior.Forever;
        }

        private class GifFrame {
            private enum FrameDisposalMethod { Replace, Combine, RestoreBackground, RestorePrevious }
            private FrameDisposalMethod Disposal { get; set; }
            public BitmapSource Bitmap { get; set; }
            public TimeSpan Delay { get; set; }

            public GifFrame(ImageSource source) {
                Disposal = FrameDisposalMethod.Replace;
                Bitmap = source as BitmapSource;
            }

            public GifFrame(BitmapFrame rawFrame, GifFrame previousFrame) {
                Disposal = FrameDisposalMethod.Replace;
                Delay = TimeSpan.FromMilliseconds(100);
                Rect rect = new Rect(0, 0, rawFrame.Width, rawFrame.Height);
                BitmapMetadata metadata = rawFrame.Metadata as BitmapMetadata;
                if (metadata != null) {
                    object value;
                    if ((value = metadata.GetQueryOrNull("/grctlext/Delay")   ) != null) Delay = TimeSpan.FromMilliseconds(10 * (ushort)value);
                    if ((value = metadata.GetQueryOrNull("/grctlext/Disposal")) != null) Disposal = (FrameDisposalMethod)(byte)value;
                    if ((value = metadata.GetQueryOrNull("/imgdesc/Left")     ) != null) rect.X = (ushort)value;
                    if ((value = metadata.GetQueryOrNull("/imgdesc/Top")      ) != null) rect.Y = (ushort)value;
                    if ((value = metadata.GetQueryOrNull("/imgdesc/Width")    ) != null) rect.Width = (ushort)value;
                    if ((value = metadata.GetQueryOrNull("/imgdesc/Height")   ) != null) rect.Height = (ushort)value;
                }
                Rect sourceRect = new Rect(0, 0, previousFrame.Bitmap.Width, previousFrame.Bitmap.Height);
                if (previousFrame.Disposal == FrameDisposalMethod.Combine || rect != sourceRect) {
                    DrawingVisual visual = new DrawingVisual();
                    using (DrawingContext context = visual.RenderOpen()) {
                        if (previousFrame.Disposal == FrameDisposalMethod.Combine)
                            context.DrawImage(previousFrame.Bitmap, sourceRect);
                        context.DrawImage(rawFrame, rect);
                    }
                    RenderTargetBitmap bmp = new RenderTargetBitmap((int)sourceRect.Width, (int)sourceRect.Height, 96, 96, PixelFormats.Pbgra32);
                    bmp.Render(visual);
                    bmp.Freeze();
                    Bitmap = bmp;
                } else Bitmap = rawFrame;
            }
        }

    }

}