Merge 6fcf75c5d9 into ad816ed988

src/ImageSharp/Formats/Ani/AniChunkType.cs

@@ -0,0 +1,70 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+namespace SixLabors.ImageSharp.Formats.Ani;
+
+internal enum AniChunkType : uint
+{
+    /// <summary>
+    /// "anih"
+    /// </summary>
+    AniH = 0x68_69_6E_61,
+
+    /// <summary>
+    /// "seq "
+    /// </summary>
+    Seq = 0x20_71_65_73,
+
+    /// <summary>
+    /// "rate"
+    /// </summary>
+    Rate = 0x65_74_61_72,
+
+    /// <summary>
+    /// "LIST"
+    /// </summary>
+    List = 0x54_53_49_4C
+}
+
+/// <summary>
+/// ListType
+/// </summary>
+internal enum AniListType : uint
+{
+    /// <summary>
+    /// "INFO" (ListType)
+    /// </summary>
+    Info = 0x4F_46_4E_49,
+
+    /// <summary>
+    /// "fram"
+    /// </summary>
+    Fram = 0x6D_61_72_66
+}
+
+/// <summary>
+/// in "INFO"
+/// </summary>
+internal enum AniListInfoType : uint
+{
+    /// <summary>
+    /// "INAM"
+    /// </summary>
+    INam = 0x4D_41_4E_49,
+
+    /// <summary>
+    /// "IART"
+    /// </summary>
+    IArt = 0x54_52_41_49
+}
+
+/// <summary>
+/// in "Fram"
+/// </summary>
+internal enum AniListFrameType : uint
+{
+    /// <summary>
+    /// "icon"
+    /// </summary>
+    Icon = 0x6E_6F_63_69
+}

src/ImageSharp/Formats/Ani/AniConfigurationModule.cs

@@ -0,0 +1,18 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+namespace SixLabors.ImageSharp.Formats.Ani;
+
+/// <summary>
+/// Registers the image encoders, decoders and mime type detectors for the Ico format.
+/// </summary>
+public sealed class AniConfigurationModule : IImageFormatConfigurationModule
+{
+    /// <inheritdoc/>
+    public void Configure(Configuration configuration)
+    {
+        // configuration.ImageFormatsManager.SetEncoder(AniFormat.Instance, new AniEncoder());
+        configuration.ImageFormatsManager.SetDecoder(AniFormat.Instance, AniDecoder.Instance);
+        configuration.ImageFormatsManager.AddImageFormatDetector(new AniImageFormatDetector());
+    }
+}

src/ImageSharp/Formats/Ani/AniConstants.cs

@@ -0,0 +1,27 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+namespace SixLabors.ImageSharp.Formats.Ani;
+
+internal static class AniConstants
+{
+    /// <summary>
+    /// Gets the header bytes identifying an ani.
+    /// </summary>
+    public const uint AniFourCc = 0x41_43_4F_4E;
+
+    /// <summary>
+    /// The list of mime types that equate to an ani.
+    /// </summary>
+    public static readonly IEnumerable<string> MimeTypes = ["application/x-navi-animation"];
+
+    /// <summary>
+    /// The list of file extensions that equate to an ani.
+    /// </summary>
+    public static readonly IEnumerable<string> FileExtensions = ["ani"];
+
+    /// <summary>
+    /// Gets the header bytes identifying an ani.
+    /// </summary>
+    public static ReadOnlySpan<byte> AniFormTypeFourCc => "ACON"u8;
+}

src/ImageSharp/Formats/Ani/AniDecoder.cs

@@ -0,0 +1,41 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+using SixLabors.ImageSharp.PixelFormats;
+
+namespace SixLabors.ImageSharp.Formats.Ani;
+
+/// <summary>
+/// Decoder for generating an image out of an ani encoded stream.
+/// </summary>
+public sealed class AniDecoder : ImageDecoder
+{
+    private AniDecoder()
+    {
+    }
+
+    /// <summary>
+    /// Gets the shared instance.
+    /// </summary>
+    public static AniDecoder Instance { get; } = new();
+
+    /// <inheritdoc/>
+    protected override Image<TPixel> Decode<TPixel>(DecoderOptions options, Stream stream, CancellationToken cancellationToken)
+    {
+        Guard.NotNull(options, nameof(options));
+        Guard.NotNull(stream, nameof(stream));
+        Image<TPixel> image = new AniDecoderCore(options).Decode<TPixel>(options.Configuration, stream, cancellationToken);
+        ScaleToTargetSize(options, image);
+        return image;
+    }
+
+    /// <inheritdoc/>
+    protected override Image Decode(DecoderOptions options, Stream stream, CancellationToken cancellationToken) => this.Decode<Rgba32>(options, stream, cancellationToken);
+
+    /// <inheritdoc/>
+    protected override ImageInfo Identify(DecoderOptions options, Stream stream, CancellationToken cancellationToken)
+    {
+        Guard.NotNull(options, nameof(options));
+        Guard.NotNull(stream, nameof(stream));
+        return new AniDecoderCore(options).Identify(options.Configuration, stream, cancellationToken);
+    }
+}

src/ImageSharp/Formats/Ani/AniDecoderCore.cs

@@ -0,0 +1,437 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using System.Buffers;
+using System.Collections;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+using System.Text;
+using SixLabors.ImageSharp.Formats.Bmp;
+using SixLabors.ImageSharp.Formats.Cur;
+using SixLabors.ImageSharp.Formats.Ico;
+using SixLabors.ImageSharp.Formats.Icon;
+using SixLabors.ImageSharp.Formats.Webp;
+using SixLabors.ImageSharp.IO;
+using SixLabors.ImageSharp.Memory;
+using SixLabors.ImageSharp.Memory.Internals;
+using SixLabors.ImageSharp.Metadata;
+
+namespace SixLabors.ImageSharp.Formats.Ani;
+
+internal class AniDecoderCore : ImageDecoderCore
+{
+    /// <summary>
+    /// The general decoder options.
+    /// </summary>
+    private readonly Configuration configuration;
+
+    /// <summary>
+    /// The stream to decode from.
+    /// </summary>
+    private BufferedReadStream currentStream = null!;
+
+    private AniHeader header;
+
+    public AniDecoderCore(DecoderOptions options)
+        : base(options) =>
+        this.configuration = options.Configuration;
+
+    protected override Image<TPixel> Decode<TPixel>(BufferedReadStream stream, CancellationToken cancellationToken)
+    {
+        this.currentStream = stream;
+
+        Guard.IsTrue(this.currentStream.TryReadUnmanaged(out RiffOrListChunkHeader riffHeader), nameof(riffHeader), "Invalid RIFF header.");
+        long dataSize = riffHeader.Size;
+        long dataStartPosition = this.currentStream.Position;
+
+        ImageMetadata metadata = new();
+        AniMetadata aniMetadata = this.ReadHeader(dataStartPosition, dataSize, metadata);
+
+        List<(AniFrameFormat Type, Image<TPixel> Image)> frames = [];
+        this.HandleRiffChunk(out Span<int> sequence, out Span<uint> rate, dataStartPosition, dataSize, aniMetadata, frames, DecodeFrameChunk);
+
+        List<ImageFrame<TPixel>> list = [];
+
+        for (int i = 0; i < sequence.Length; i++)
+        {
+            int sequenceIndex = sequence[i];
+            (AniFrameFormat type, Image<TPixel>? img) = frames[sequenceIndex];
+
+            AniFrameMetadata aniFrameMetadata = new()
+            {
+                FrameDelay = rate.IsEmpty ? aniMetadata.DisplayRate : rate[sequenceIndex],
+                SequenceNumber = i
+            };
+
+            list.AddRange(img.Frames.Select(source =>
+            {
+                ImageFrame<TPixel> target = new(this.Options.Configuration, this.Dimensions);
+                for (int y = 0; y < source.Height; y++)
+                {
+                    source.PixelBuffer.DangerousGetRowSpan(y).CopyTo(target.PixelBuffer.DangerousGetRowSpan(y));
+                }
+
+                AniFrameMetadata clonedMetadata = aniFrameMetadata.DeepClone();
+                source.Metadata.SetFormatMetadata(AniFormat.Instance, clonedMetadata);
+                clonedMetadata.FrameFormat = type;
+                switch (type)
+                {
+                    case AniFrameFormat.Ico:
+                        IcoFrameMetadata icoFrameMetadata = source.Metadata.GetIcoMetadata();
+
+                        // TODO source.Metadata.SetFormatMetadata(IcoFormat.Instance, null);
+                        clonedMetadata.IcoFrameMetadata = icoFrameMetadata;
+                        clonedMetadata.EncodingWidth = icoFrameMetadata.EncodingWidth;
+                        clonedMetadata.EncodingHeight = icoFrameMetadata.EncodingHeight;
+                        break;
+                    case AniFrameFormat.Cur:
+                        CurFrameMetadata curFrameMetadata = source.Metadata.GetCurMetadata();
+
+                        // TODO source.Metadata.SetFormatMetadata(CurFormat.Instance, null);
+                        clonedMetadata.CurFrameMetadata = curFrameMetadata;
+                        clonedMetadata.EncodingWidth = curFrameMetadata.EncodingWidth;
+                        clonedMetadata.EncodingHeight = curFrameMetadata.EncodingHeight;
+                        break;
+                    case AniFrameFormat.Bmp:
+                        clonedMetadata.EncodingWidth = Narrow(source.Width);
+                        clonedMetadata.EncodingHeight = Narrow(source.Height);
+                        break;
+                    default:
+                        break;
+                }
+
+                return target;
+            }));
+        }
+
+        foreach ((AniFrameFormat _, Image<TPixel> img) in frames)
+        {
+            img.Dispose();
+        }
+
+        Image<TPixel> image = new(this.Options.Configuration, metadata, list);
+
+        return image;
+
+        void DecodeFrameChunk()
+        {
+            while (this.TryReadChunk(dataStartPosition, dataSize, out RiffChunkHeader chunk))
+            {
+                if ((AniListFrameType)chunk.FourCc is not AniListFrameType.Icon)
+                {
+                    continue;
+                }
+
+                long endPosition = this.currentStream.Position + chunk.Size;
+                Image<TPixel>? frame = null;
+                AniFrameFormat type = default;
+                if (aniMetadata.Flags.HasFlag(AniHeaderFlags.IsIcon))
+                {
+                    if (this.currentStream.TryReadUnmanaged(out IconDir dir))
+                    {
+                        this.currentStream.Position -= Unsafe.SizeOf<IconDir>();
+
+                        switch (dir.Type)
+                        {
+                            case IconFileType.CUR:
+                                frame = CurDecoder.Instance.Decode<TPixel>(this.Options, this.currentStream);
+                                type = AniFrameFormat.Cur;
+                                break;
+                            case IconFileType.ICO:
+                                frame = IcoDecoder.Instance.Decode<TPixel>(this.Options, this.currentStream);
+                                type = AniFrameFormat.Ico;
+                                break;
+                        }
+                    }
+                }
+                else
+                {
+                    frame = BmpDecoder.Instance.Decode<TPixel>(this.Options, this.currentStream);
+                    type = AniFrameFormat.Bmp;
+                }
+
+                if (frame is not null)
+                {
+                    frames.Add((type, frame));
+                    this.Dimensions = new(Math.Max(this.Dimensions.Width, frame.Size.Width), Math.Max(this.Dimensions.Height, frame.Size.Height));
+                }
+
+                this.currentStream.Position = endPosition;
+            }
+        }
+    }
+
+    protected override ImageInfo Identify(BufferedReadStream stream, CancellationToken cancellationToken)
+    {
+        this.currentStream = stream;
+
+        Guard.IsTrue(this.currentStream.TryReadUnmanaged(out RiffOrListChunkHeader riffHeader), nameof(riffHeader), "Invalid RIFF header.");
+        long dataSize = riffHeader.Size;
+        long dataStartPosition = this.currentStream.Position;
+
+        ImageMetadata metadata = new();
+        AniMetadata aniMetadata = this.ReadHeader(dataStartPosition, dataSize, metadata);
+
+        List<(AniFrameFormat Type, ImageInfo Info)> infoList = [];
+        this.HandleRiffChunk(out Span<int> sequence, out Span<uint> rate, dataStartPosition, dataSize, aniMetadata, infoList, IdentifyFrameChunk);
+
+        List<ImageFrameMetadata> frameMetadataCollection = new(sequence.Length);
+
+        for (int i = 0; i < sequence.Length; i++)
+        {
+            int sequenceIndex = sequence[i];
+            (AniFrameFormat type, ImageInfo info) = infoList[sequenceIndex];
+
+            AniFrameMetadata aniFrameMetadata = new()
+            {
+                FrameDelay = rate.IsEmpty ? aniMetadata.DisplayRate : rate[sequenceIndex],
+                SequenceNumber = i
+            };
+
+            if (info.FrameMetadataCollection.Count is not 0)
+            {
+                frameMetadataCollection.AddRange(
+                    info.FrameMetadataCollection.Select(frameMetadata =>
+                    {
+                        AniFrameMetadata clonedMetadata = aniFrameMetadata.DeepClone();
+                        frameMetadata.SetFormatMetadata(AniFormat.Instance, clonedMetadata);
+                        clonedMetadata.FrameFormat = type;
+                        switch (type)
+                        {
+                            case AniFrameFormat.Ico:
+                                IcoFrameMetadata icoFrameMetadata = frameMetadata.GetIcoMetadata();
+
+                                // TODO source.Metadata.SetFormatMetadata(IcoFormat.Instance, null);
+                                clonedMetadata.IcoFrameMetadata = icoFrameMetadata;
+                                clonedMetadata.EncodingWidth = icoFrameMetadata.EncodingWidth;
+                                clonedMetadata.EncodingHeight = icoFrameMetadata.EncodingHeight;
+                                break;
+                            case AniFrameFormat.Cur:
+                                CurFrameMetadata curFrameMetadata = frameMetadata.GetCurMetadata();
+
+                                // TODO source.Metadata.SetFormatMetadata(CurFormat.Instance, null);
+                                clonedMetadata.CurFrameMetadata = curFrameMetadata;
+                                clonedMetadata.EncodingWidth = curFrameMetadata.EncodingWidth;
+                                clonedMetadata.EncodingHeight = curFrameMetadata.EncodingHeight;
+                                break;
+                            default:
+                                ThrowHelper.ThrowArgumentOutOfRangeException(nameof(type), "FrameMetadata must be ICO or CUR");
+                                break;
+                        }
+
+                        return frameMetadata;
+                    }));
+            }
+            else
+            {
+                // BMP
+                aniFrameMetadata.EncodingWidth = Narrow(info.Width);
+                aniFrameMetadata.EncodingHeight = Narrow(info.Height);
+                aniFrameMetadata.FrameFormat = type;
+                ImageFrameMetadata frameMetadata = new();
+                frameMetadata.SetFormatMetadata(AniFormat.Instance, aniFrameMetadata);
+                frameMetadataCollection.Add(frameMetadata);
+            }
+        }
+
+        ImageInfo imageInfo = new(this.Dimensions, metadata, frameMetadataCollection);
+
+        return imageInfo;
+
+        void IdentifyFrameChunk()
+        {
+            while (this.TryReadChunk(dataStartPosition, dataSize, out RiffChunkHeader chunk))
+            {
+                if ((AniListFrameType)chunk.FourCc is not AniListFrameType.Icon)
+                {
+                    continue;
+                }
+
+                long endPosition = this.currentStream.Position + chunk.Size;
+                ImageInfo? info = null;
+                AniFrameFormat type = default;
+                if (aniMetadata.Flags.HasFlag(AniHeaderFlags.IsIcon))
+                {
+                    if (this.currentStream.TryReadUnmanaged(out IconDir dir))
+                    {
+                        this.currentStream.Position -= Unsafe.SizeOf<IconDir>();
+
+                        switch (dir.Type)
+                        {
+                            // TODO: Use Core decoders.
+                            case IconFileType.CUR:
+                                info = CurDecoder.Instance.Identify(this.Options, this.currentStream);
+                                type = AniFrameFormat.Cur;
+                                break;
+                            case IconFileType.ICO:
+                                info = IcoDecoder.Instance.Identify(this.Options, this.currentStream);
+                                type = AniFrameFormat.Ico;
+                                break;
+                        }
+                    }
+                }
+                else
+                {
+                    // TODO: Use Core decoders.
+                    info = BmpDecoder.Instance.Identify(this.Options, this.currentStream);
+                    type = AniFrameFormat.Bmp;
+                }
+
+                if (info is not null)
+                {
+                    infoList.Add((type, info));
+                    this.Dimensions = new(Math.Max(this.Dimensions.Width, info.Size.Width), Math.Max(this.Dimensions.Height, info.Size.Height));
+                }
+
+                this.currentStream.Position = endPosition;
+            }
+        }
+    }
+
+    private AniMetadata ReadHeader(long dataStartPosition, long dataSize, ImageMetadata metadata)
+    {
+        if (!this.TryReadChunk(dataStartPosition, dataSize, out RiffChunkHeader riffChunkHeader) ||
+            (AniChunkType)riffChunkHeader.FourCc is not AniChunkType.AniH)
+        {
+            Guard.IsTrue(false, nameof(riffChunkHeader), "Missing ANIH chunk.");
+        }
+
+        AniMetadata aniMetadata = metadata.GetAniMetadata();
+
+        if (this.currentStream.TryReadUnmanaged(out AniHeader result))
+        {
+            this.header = result;
+            aniMetadata.Width = result.Width;
+            aniMetadata.Height = result.Height;
+            aniMetadata.BitCount = result.BitCount;
+            aniMetadata.Planes = result.Planes;
+            aniMetadata.DisplayRate = result.DisplayRate;
+            aniMetadata.Flags = result.Flags;
+        }
+
+        return aniMetadata;
+    }
+
+    /// <summary>
+    /// Call <see cref="HandleRiffChunk"/> <br/>
+    /// -> Call <see cref="HandleListChunk"/> <br/>
+    /// -> Call <paramref name="handleFrameChunk"/>
+    /// </summary>
+    private void HandleRiffChunk(out Span<int> sequence, out Span<uint> rate, long dataStartPosition, long dataSize, AniMetadata aniMetadata, ICollection totalFrameCount, Action handleFrameChunk)
+    {
+        sequence = default;
+        rate = default;
+
+        while (this.TryReadChunk(dataStartPosition, dataSize, out RiffChunkHeader chunk))
+        {
+            switch ((AniChunkType)chunk.FourCc)
+            {
+                case AniChunkType.Seq:
+                {
+                    using IMemoryOwner<byte> data = this.ReadChunkData(chunk.Size);
+                    sequence = MemoryMarshal.Cast<byte, int>(data.Memory.Span);
+                    break;
+                }
+
+                case AniChunkType.Rate:
+                {
+                    using IMemoryOwner<byte> data = this.ReadChunkData(chunk.Size);
+                    rate = MemoryMarshal.Cast<byte, uint>(data.Memory.Span);
+                    break;
+                }
+
+                case AniChunkType.List:
+                    this.HandleListChunk(dataStartPosition, dataSize, aniMetadata, handleFrameChunk);
+                    break;
+                default:
+                    break;
+            }
+        }
+
+        if (sequence.IsEmpty)
+        {
+            sequence = Enumerable.Range(0, totalFrameCount.Count).ToArray();
+        }
+    }
+
+    private void HandleListChunk(long dataStartPosition, long dataSize, AniMetadata aniMetadata, Action handleFrameChunk)
+    {
+        if (!this.currentStream.TryReadUnmanaged(out uint listType))
+        {
+            return;
+        }
+
+        switch ((AniListType)listType)
+        {
+            case AniListType.Fram:
+            {
+                handleFrameChunk();
+                break;
+            }
+
+            case AniListType.Info:
+            {
+                while (this.TryReadChunk(dataStartPosition, dataSize, out RiffChunkHeader chunk))
+                {
+                    switch ((AniListInfoType)chunk.FourCc)
+                    {
+                        case AniListInfoType.INam:
+                        {
+                            using IMemoryOwner<byte> data = this.ReadChunkData(chunk.Size);
+                            aniMetadata.Name = Encoding.ASCII.GetString(data.Memory.Span).TrimEnd('\0');
+                            break;
+                        }
+
+                        case AniListInfoType.IArt:
+                        {
+                            using IMemoryOwner<byte> data = this.ReadChunkData(chunk.Size);
+                            aniMetadata.Artist = Encoding.ASCII.GetString(data.Memory.Span).TrimEnd('\0');
+                            break;
+                        }
+
+                        default:
+                            break;
+                    }
+                }
+
+                break;
+            }
+        }
+    }
+
+    private bool TryReadChunk(long startPosition, long size, out RiffChunkHeader chunk)
+    {
+        if (this.currentStream.Position - startPosition >= size)
+        {
+            chunk = default;
+            return false;
+        }
+
+        return this.currentStream.TryReadUnmanaged(out chunk);
+    }
+
+    /// <summary>
+    /// Reads the chunk data from the stream.
+    /// </summary>
+    /// <param name="length">The length of the chunk data to read.</param>
+    [MethodImpl(InliningOptions.ShortMethod)]
+    private IMemoryOwner<byte> ReadChunkData(uint length)
+    {
+        if (length is 0)
+        {
+            return new BasicArrayBuffer<byte>([]);
+        }
+
+        // We rent the buffer here to return it afterwards in Decode()
+        // We don't want to throw a degenerated memory exception here as we want to allow partial decoding
+        // so limit the length.
+        int len = (int)Math.Min(length, this.currentStream.Length - this.currentStream.Position);
+        IMemoryOwner<byte> buffer = this.configuration.MemoryAllocator.Allocate<byte>(len, AllocationOptions.Clean);
+
+        this.currentStream.Read(buffer.GetSpan(), 0, len);
+
+        return buffer;
+    }
+
+    private static byte Narrow(int value) => value > byte.MaxValue ? (byte)0 : (byte)value;
+}

src/ImageSharp/Formats/Ani/AniFormat.cs

@@ -0,0 +1,33 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+namespace SixLabors.ImageSharp.Formats.Ani;
+
+/// <summary>
+/// Registers the image encoders, decoders and mime type detectors for the bmp format.
+/// </summary>
+public sealed class AniFormat : IImageFormat<AniMetadata, AniFrameMetadata>
+{
+    /// <summary>
+    /// Gets the shared instance.
+    /// </summary>
+    public static AniFormat Instance { get; } = new();
+
+    /// <inheritdoc/>
+    public string Name => "ANI";
+
+    /// <inheritdoc/>
+    public string DefaultMimeType => "application/x-navi-animation";
+
+    /// <inheritdoc/>
+    public IEnumerable<string> MimeTypes => AniConstants.MimeTypes;
+
+    /// <inheritdoc/>
+    public IEnumerable<string> FileExtensions => AniConstants.FileExtensions;
+
+    /// <inheritdoc/>
+    public AniMetadata CreateDefaultFormatMetadata() => new();
+
+    /// <inheritdoc/>
+    public AniFrameMetadata CreateDefaultFormatFrameMetadata() => new();
+}

src/ImageSharp/Formats/Ani/AniFrameFormat.cs

@@ -0,0 +1,25 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+namespace SixLabors.ImageSharp.Formats.Ani;
+
+/// <summary>
+/// Specifies the format of the frame data.
+/// </summary>
+public enum AniFrameFormat
+{
+    /// <summary>
+    /// The frame data is in ICO format.
+    /// </summary>
+    Ico = 1,
+
+    /// <summary>
+    /// The frame data is in CUR format.
+    /// </summary>
+    Cur,
+
+    /// <summary>
+    /// The frame data is in BMP format.
+    /// </summary>
+    Bmp
+}

src/ImageSharp/Formats/Ani/AniFrameMetadata.cs

@@ -0,0 +1,97 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using System.Numerics;
+using SixLabors.ImageSharp.Formats.Cur;
+using SixLabors.ImageSharp.Formats.Ico;
+using SixLabors.ImageSharp.PixelFormats;
+
+namespace SixLabors.ImageSharp.Formats.Ani;
+
+/// <summary>
+/// Provides Ani specific metadata information for the image.
+/// </summary>
+public class AniFrameMetadata : IFormatFrameMetadata<AniFrameMetadata>
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="AniFrameMetadata"/> class.
+    /// </summary>
+    public AniFrameMetadata()
+    {
+    }
+
+    /// <summary>
+    /// Gets or sets the display time for this frame (in 1/60 seconds)
+    /// </summary>
+    public uint FrameDelay { get; set; }
+
+    /// <summary>
+    /// Gets or sets the sequence number of current frame.
+    /// </summary>
+    public int SequenceNumber { get; set; } = 1;
+
+    /// <summary>
+    /// Gets or sets the encoding width. <br />
+    /// Can be any number between 0 and 255. Value 0 means a frame height of 256 pixels or greater.
+    /// </summary>
+    public byte? EncodingWidth { get; set; }
+
+    /// <summary>
+    /// Gets or sets the encoding height. <br />
+    /// Can be any number between 0 and 255. Value 0 means a frame height of 256 pixels or greater.
+    /// </summary>
+    public byte? EncodingHeight { get; set; }
+
+    /// <summary>
+    /// Gets or sets a value indicating whether the frame will be encoded as an ICO or CUR or BMP file.
+    /// </summary>
+    public AniFrameFormat FrameFormat { get; set; }
+
+    /// <summary>
+    /// Gets or sets the <see cref="IcoFrameMetadata"/> of one "icon" chunk.
+    /// </summary>
+    public IcoFrameMetadata? IcoFrameMetadata { get; set; }
+
+    /// <summary>
+    /// Gets or sets the <see cref="CurFrameMetadata"/> of one "icon" chunk.
+    /// </summary>
+    public CurFrameMetadata? CurFrameMetadata { get; set; }
+
+    /// <inheritdoc/>
+    public static AniFrameMetadata FromFormatConnectingFrameMetadata(FormatConnectingFrameMetadata metadata) =>
+        new()
+        {
+            FrameDelay = (uint)metadata.Duration.TotalSeconds * 60
+        };
+
+    /// <inheritdoc/>
+    IDeepCloneable IDeepCloneable.DeepClone() => this.DeepClone();
+
+    /// <inheritdoc/>
+    public FormatConnectingFrameMetadata ToFormatConnectingFrameMetadata()
+    {
+        // TODO: Implement. You need to consider encoding width/height.
+        return new() { Duration = TimeSpan.FromSeconds(this.FrameDelay / 60d) };
+    }
+
+    /// <inheritdoc/>
+    public void AfterFrameApply<TPixel>(ImageFrame<TPixel> source, ImageFrame<TPixel> destination, Matrix4x4 matrix)
+        where TPixel : unmanaged, IPixel<TPixel>
+    {
+        // TODO: Implement. You need to consider encoding width/height.
+    }
+
+    /// <inheritdoc/>
+    public AniFrameMetadata DeepClone() => new()
+    {
+        FrameDelay = this.FrameDelay,
+        EncodingHeight = this.EncodingHeight,
+        EncodingWidth = this.EncodingWidth,
+        SequenceNumber = this.SequenceNumber,
+        FrameFormat = this.FrameFormat,
+        IcoFrameMetadata = this.IcoFrameMetadata?.DeepClone(),
+        CurFrameMetadata = this.CurFrameMetadata?.DeepClone(),
+
+        // TODO SubImageMetadata
+    };
+}

src/ImageSharp/Formats/Ani/AniHeader.cs

@@ -0,0 +1,32 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+
+namespace SixLabors.ImageSharp.Formats.Ani;
+
+internal readonly struct AniHeader
+{
+    public uint Size { get; }
+
+    public uint Frames { get; }
+
+    public uint Steps { get; }
+
+    public uint Width { get; }
+
+    public uint Height { get; }
+
+    public uint BitCount { get; }
+
+    public uint Planes { get; }
+
+    public uint DisplayRate { get; }
+
+    public AniHeaderFlags Flags { get; }
+
+    public static ref AniHeader Parse(ReadOnlySpan<byte> data) => ref Unsafe.As<byte, AniHeader>(ref MemoryMarshal.GetReference(data));
+
+    public void WriteTo(Stream stream) => stream.Write(MemoryMarshal.AsBytes(MemoryMarshal.CreateReadOnlySpan(in this, 1)));
+}

src/ImageSharp/Formats/Ani/AniHeaderFlags.cs

@@ -0,0 +1,21 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+namespace SixLabors.ImageSharp.Formats.Ani;
+
+/// <summary>
+/// Flags for the ANI header.
+/// </summary>
+[Flags]
+public enum AniHeaderFlags : uint
+{
+    /// <summary>
+    /// If set, the ANI file's "icon" chunk contains an ICO or CUR file, otherwise it contains a BMP file.
+    /// </summary>
+    IsIcon = 1,
+
+    /// <summary>
+    /// If set, the ANI file contains a "seq " chunk.
+    /// </summary>
+    ContainsSeq = 2
+}

src/ImageSharp/Formats/Ani/AniImageFormatDetector.cs

@@ -0,0 +1,30 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using System.Diagnostics.CodeAnalysis;
+using SixLabors.ImageSharp.Formats.Webp;
+
+namespace SixLabors.ImageSharp.Formats.Ani;
+
+/// <summary>
+/// Detects ico file headers.
+/// </summary>
+public class AniImageFormatDetector : IImageFormatDetector
+{
+    /// <inheritdoc/>
+    public int HeaderSize => RiffOrListChunkHeader.HeaderSize;
+
+    /// <inheritdoc/>
+    public bool TryDetectFormat(ReadOnlySpan<byte> header, [NotNullWhen(true)] out IImageFormat? format)
+    {
+        format = this.IsSupportedFileFormat(header) ? AniFormat.Instance : null;
+        return format is not null;
+    }
+
+    private bool IsSupportedFileFormat(ReadOnlySpan<byte> header)
+        => header.Length >= this.HeaderSize && RiffOrListChunkHeader.Parse(header) is
+        {
+            IsRiff: true,
+            FormType: AniConstants.AniFourCc
+        };
+}

src/ImageSharp/Formats/Ani/AniMetadata.cs

@@ -0,0 +1,108 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using System.Numerics;
+using SixLabors.ImageSharp.PixelFormats;
+
+namespace SixLabors.ImageSharp.Formats.Ani;
+
+/// <summary>
+/// Provides Ani specific metadata information for the image.
+/// </summary>
+public class AniMetadata : IFormatMetadata<AniMetadata>
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="AniMetadata"/> class.
+    /// </summary>
+    public AniMetadata()
+    {
+    }
+
+    /// <summary>
+    /// Gets or sets the width of frames in the animation.
+    /// </summary>
+    /// <remarks>
+    /// Remains zero when <see cref="Flags"/> has flag <see cref="AniHeaderFlags.IsIcon"/>
+    /// </remarks>
+    public uint Width { get; set; }
+
+    /// <summary>
+    /// Gets or sets the height of frames in the animation.
+    /// </summary>
+    /// <remarks>
+    /// Remains zero when <see cref="Flags"/> has flag <see cref="AniHeaderFlags.IsIcon"/>
+    /// </remarks>
+    public uint Height { get; set; }
+
+    /// <summary>
+    /// Gets or sets the number of bits per pixel.
+    /// </summary>
+    /// <remarks>
+    /// Remains zero when <see cref="Flags"/> has flag <see cref="AniHeaderFlags.IsIcon"/>
+    /// </remarks>
+    public uint BitCount { get; set; }
+
+    /// <summary>
+    /// Gets or sets the number of frames in the animation.
+    /// </summary>
+    /// <remarks>
+    /// Remains zero when <see cref="Flags"/> has flag <see cref="AniHeaderFlags.IsIcon"/>
+    /// </remarks>
+    public uint Planes { get; set; }
+
+    /// <summary>
+    /// Gets or sets the default display rate of frames in the animation.
+    /// </summary>
+    public uint DisplayRate { get; set; }
+
+    /// <summary>
+    /// Gets or sets the flags for the ANI header.
+    /// </summary>
+    public AniHeaderFlags Flags { get; set; }
+
+    /// <summary>
+    /// Gets or sets the name of the ANI file.
+    /// </summary>
+    public string? Name { get; set; }
+
+    /// <summary>
+    /// Gets or sets the artist of the ANI file.
+    /// </summary>
+    public string? Artist { get; set; }
+
+    /// <inheritdoc/>
+    public static AniMetadata FromFormatConnectingMetadata(FormatConnectingMetadata metadata)
+        => throw new NotImplementedException();
+
+    /// <inheritdoc/>
+    public void AfterImageApply<TPixel>(Image<TPixel> destination, Matrix4x4 matrix)
+            where TPixel : unmanaged, IPixel<TPixel>
+    {
+    }
+
+    /// <inheritdoc/>
+    IDeepCloneable IDeepCloneable.DeepClone() => this.DeepClone();
+
+    /// <inheritdoc/>
+    public PixelTypeInfo GetPixelTypeInfo()
+        => throw new NotImplementedException();
+
+    /// <inheritdoc/>
+    public FormatConnectingMetadata ToFormatConnectingMetadata()
+        => throw new NotImplementedException();
+
+    /// <inheritdoc/>
+    public AniMetadata DeepClone() => new()
+    {
+        Width = this.Width,
+        Height = this.Height,
+        BitCount = this.BitCount,
+        Planes = this.Planes,
+        DisplayRate = this.DisplayRate,
+        Flags = this.Flags,
+        Name = this.Name,
+        Artist = this.Artist
+
+        // TODO IconFrames
+    };
+}

src/ImageSharp/Formats/Icon/IconDir.cs

@@ -1,29 +1,30 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
+using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 
 namespace SixLabors.ImageSharp.Formats.Icon;
 
 [StructLayout(LayoutKind.Sequential, Pack = 1, Size = Size)]
-internal struct IconDir(ushort reserved, IconFileType type, ushort count)
+internal struct IconDir
 {
     public const int Size = 3 * sizeof(ushort);
 
     /// <summary>
     /// Reserved. Must always be 0.
     /// </summary>
-    public ushort Reserved = reserved;
+    public ushort Reserved;
 
     /// <summary>
     /// Specifies image type: 1 for icon (.ICO) image, 2 for cursor (.CUR) image. Other values are invalid.
     /// </summary>
-    public IconFileType Type = type;
+    public IconFileType Type;
 
     /// <summary>
     /// Specifies number of images in the file.
     /// </summary>
-    public ushort Count = count;
+    public ushort Count;
 
     public IconDir(IconFileType type)
         : this(type, 0)
@@ -35,9 +36,16 @@ internal struct IconDir(ushort reserved, IconFileType type, ushort count)
     {
     }
 
-    public static IconDir Parse(ReadOnlySpan<byte> data)
-        => MemoryMarshal.Cast<byte, IconDir>(data)[0];
+    public IconDir(ushort reserved, IconFileType type, ushort count)
+    {
+        this.Reserved = reserved;
+        this.Type = type;
+        this.Count = count;
+    }
+
+    public static ref IconDir Parse(ReadOnlySpan<byte> data)
+        => ref Unsafe.As<byte, IconDir>(ref MemoryMarshal.GetReference(data));
 
-    public readonly unsafe void WriteTo(Stream stream)
-        => stream.Write(MemoryMarshal.Cast<IconDir, byte>([this]));
+    public readonly void WriteTo(Stream stream)
+        => stream.Write(MemoryMarshal.AsBytes(MemoryMarshal.CreateReadOnlySpan(in this, 1)));
 }

src/ImageSharp/Formats/Icon/IconDirEntry.cs

@@ -1,6 +1,7 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
+using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 
 namespace SixLabors.ImageSharp.Formats.Icon;
@@ -52,9 +53,9 @@ internal struct IconDirEntry
     /// </summary>
     public uint ImageOffset;
 
-    public static IconDirEntry Parse(in ReadOnlySpan<byte> data)
-        => MemoryMarshal.Cast<byte, IconDirEntry>(data)[0];
+    public static ref IconDirEntry Parse(in ReadOnlySpan<byte> data)
+        => ref Unsafe.As<byte, IconDirEntry>(ref MemoryMarshal.GetReference(data));
 
-    public readonly unsafe void WriteTo(in Stream stream)
-        => stream.Write(MemoryMarshal.Cast<IconDirEntry, byte>([this]));
+    public readonly void WriteTo(in Stream stream)
+        => stream.Write(MemoryMarshal.AsBytes(MemoryMarshal.CreateReadOnlySpan(in this, 1)));
 }

src/ImageSharp/Formats/Icon/IconFileType.cs

@@ -16,5 +16,5 @@ internal enum IconFileType : ushort
     /// <summary>
     /// CUR file
     /// </summary>
-    CUR = 2,
+    CUR = 2
 }

src/ImageSharp/Formats/Webp/BitWriter/BitWriterBase.cs

@@ -100,7 +100,7 @@ internal abstract class BitWriterBase
         bool hasAnimation)
     {
         // Write file size later
-        RiffHelper.BeginWriteRiffFile(stream, WebpConstants.WebpFourCc);
+        RiffHelper.BeginWriteRiff(stream, WebpConstants.WebpFormTypeFourCc);
 
         // Write VP8X, header if necessary.
         WebpVp8X vp8x = default;
@@ -151,7 +151,7 @@ internal abstract class BitWriterBase
             RiffHelper.WriteChunk(stream, (uint)WebpChunkType.Xmp, xmpProfile.Data);
         }
 
-        RiffHelper.EndWriteRiffFile(stream, in vp8x, updateVp8x, initialPosition);
+        RiffHelper.EndWriteVp8X(stream, in vp8x, updateVp8x, initialPosition);
     }
 
     /// <summary>
@@ -189,7 +189,7 @@ internal abstract class BitWriterBase
 
         stream.WriteByte(flags);
         stream.Write(dataBytes);
-        RiffHelper.EndWriteChunk(stream, pos);
+        RiffHelper.EndWriteChunk(stream, pos, 2);
     }
 
     /// <summary>

src/ImageSharp/Formats/Webp/Chunks/WebpVp8X.cs

@@ -130,6 +130,6 @@ internal readonly struct WebpVp8X : IEquatable<WebpVp8X>
         WebpChunkParsingUtils.WriteUInt24LittleEndian(stream, this.Width - 1);
         WebpChunkParsingUtils.WriteUInt24LittleEndian(stream, this.Height - 1);
 
-        RiffHelper.EndWriteChunk(stream, pos);
+        RiffHelper.EndWriteChunk(stream, pos, 2);
     }
 }

src/ImageSharp/Formats/Webp/Lossless/Vp8LEncoder.cs

@@ -315,7 +315,7 @@ internal class Vp8LEncoder : IDisposable
 
         if (hasAnimation)
         {
-            RiffHelper.EndWriteChunk(stream, prevPosition);
+            RiffHelper.EndWriteChunk(stream, prevPosition, 2);
         }
 
         return hasAlpha;

src/ImageSharp/Formats/Webp/Lossy/Vp8Encoder.cs

@@ -517,7 +517,7 @@ internal class Vp8Encoder : IDisposable
 
             if (hasAnimation)
             {
-                RiffHelper.EndWriteChunk(stream, prevPosition);
+                RiffHelper.EndWriteChunk(stream, prevPosition, 2);
             }
         }
         finally

src/ImageSharp/Formats/Webp/RiffChunkHeader.cs

@@ -0,0 +1,16 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+
+namespace SixLabors.ImageSharp.Formats.Webp;
+
+internal readonly struct RiffChunkHeader
+{
+    public readonly uint FourCc;
+
+    public readonly uint Size;
+
+    public ReadOnlySpan<byte> FourCcBytes => MemoryMarshal.CreateReadOnlySpan(ref Unsafe.As<uint, byte>(ref Unsafe.AsRef(in this.FourCc)), sizeof(uint));
+}

src/ImageSharp/Formats/Webp/RiffHelper.cs

@@ -2,137 +2,93 @@
 // Licensed under the Six Labors Split License.
 
 using System.Buffers.Binary;
-using System.Text;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
 using SixLabors.ImageSharp.Formats.Webp.Chunks;
 
 namespace SixLabors.ImageSharp.Formats.Webp;
 
 internal static class RiffHelper
 {
-    /// <summary>
-    /// The header bytes identifying RIFF file.
-    /// </summary>
-    private const uint RiffFourCc = 0x52_49_46_46;
+    public static void WriteChunk(Stream stream, uint fourCc, ReadOnlySpan<byte> data)
+    {
+        long pos = BeginWriteChunk(stream, fourCc);
+        stream.Write(data);
+        EndWriteChunk(stream, pos);
+    }
 
-    public static void WriteRiffFile(Stream stream, string formType, Action<Stream> func) =>
-        WriteChunk(stream, RiffFourCc, s =>
-        {
-            s.Write(Encoding.ASCII.GetBytes(formType));
-            func(s);
-        });
+    public static void WriteChunk<TStruct>(Stream stream, uint fourCc, in TStruct chunk)
+        where TStruct : unmanaged =>
+        WriteChunk(stream, fourCc, MemoryMarshal.AsBytes(MemoryMarshal.CreateReadOnlySpan(in chunk, 1)));
 
-    public static void WriteChunk(Stream stream, uint fourCc, Action<Stream> func)
+    public static long BeginWriteChunk(Stream stream, ReadOnlySpan<byte> fourCc)
     {
-        Span<byte> buffer = stackalloc byte[4];
-
         // write the fourCC
-        BinaryPrimitives.WriteUInt32BigEndian(buffer, fourCc);
-        stream.Write(buffer);
+        stream.Write(fourCc);
 
         long sizePosition = stream.Position;
-        stream.Position += 4;
-
-        func(stream);
-
-        long position = stream.Position;
 
-        uint dataSize = (uint)(position - sizePosition - 4);
-
-        // padding
-        if (dataSize % 2 == 1)
-        {
-            stream.WriteByte(0);
-            position++;
-        }
+        // Leaving the place for the size
+        stream.Position += 4;
 
-        BinaryPrimitives.WriteUInt32LittleEndian(buffer, dataSize);
-        stream.Position = sizePosition;
-        stream.Write(buffer);
-        stream.Position = position;
+        return sizePosition;
     }
 
-    public static void WriteChunk(Stream stream, uint fourCc, ReadOnlySpan<byte> data)
+    public static long BeginWriteChunk(Stream stream, uint fourCc)
     {
         Span<byte> buffer = stackalloc byte[4];
-
-        // write the fourCC
         BinaryPrimitives.WriteUInt32BigEndian(buffer, fourCc);
-        stream.Write(buffer);
-        uint size = (uint)data.Length;
-        BinaryPrimitives.WriteUInt32LittleEndian(buffer, size);
-        stream.Write(buffer);
-        stream.Write(data);
-
-        // padding
-        if (size % 2 is 1)
-        {
-            stream.WriteByte(0);
-        }
+        return BeginWriteChunk(stream, buffer);
     }
 
-    public static unsafe void WriteChunk<TStruct>(Stream stream, uint fourCc, in TStruct chunk)
-        where TStruct : unmanaged
+    public static long BeginWriteRiff(Stream stream, ReadOnlySpan<byte> formType)
     {
-        fixed (TStruct* ptr = &chunk)
-        {
-            WriteChunk(stream, fourCc, new Span<byte>(ptr, sizeof(TStruct)));
-        }
+        long sizePosition = BeginWriteChunk(stream, "RIFF"u8);
+        stream.Write(formType);
+        return sizePosition;
     }
 
-    public static long BeginWriteChunk(Stream stream, uint fourCc)
+    public static long BeginWriteList(Stream stream, ReadOnlySpan<byte> listType)
     {
-        Span<byte> buffer = stackalloc byte[4];
-
-        // write the fourCC
-        BinaryPrimitives.WriteUInt32BigEndian(buffer, fourCc);
-        stream.Write(buffer);
-
-        long sizePosition = stream.Position;
-        stream.Position += 4;
-
+        long sizePosition = BeginWriteChunk(stream, "LIST"u8);
+        stream.Write(listType);
         return sizePosition;
     }
 
-    public static void EndWriteChunk(Stream stream, long sizePosition)
+    public static void EndWriteChunk(Stream stream, long sizePosition, int alignment = 1)
     {
-        Span<byte> buffer = stackalloc byte[4];
+        Guard.MustBeGreaterThan(alignment, 0, nameof(alignment));
 
-        long position = stream.Position;
+        long currentPosition = stream.Position;
 
-        uint dataSize = (uint)(position - sizePosition - 4);
+        uint dataSize = (uint)(currentPosition - sizePosition - 4);
 
-        // padding
-        if (dataSize % 2 is 1)
+        // Add padding
+        while (dataSize % alignment is not 0)
         {
             stream.WriteByte(0);
-            position++;
+            dataSize++;
+            currentPosition++;
         }
 
         // Add the size of the encoded file to the Riff header.
-        BinaryPrimitives.WriteUInt32LittleEndian(buffer, dataSize);
         stream.Position = sizePosition;
-        stream.Write(buffer);
-        stream.Position = position;
-    }
-
-    public static long BeginWriteRiffFile(Stream stream, string formType)
-    {
-        long sizePosition = BeginWriteChunk(stream, RiffFourCc);
-        stream.Write(Encoding.ASCII.GetBytes(formType));
-        return sizePosition;
+        stream.Write(MemoryMarshal.CreateReadOnlySpan(ref Unsafe.As<uint, byte>(ref dataSize), sizeof(uint)));
+        stream.Position = currentPosition;
     }
 
-    public static void EndWriteRiffFile(Stream stream, in WebpVp8X vp8x, bool updateVp8x, long sizePosition)
+    public static void EndWriteVp8X(Stream stream, in WebpVp8X vp8X, bool updateVp8X, long initPosition)
     {
-        EndWriteChunk(stream, sizePosition + 4);
+        // Jump through "RIFF" fourCC
+        EndWriteChunk(stream, initPosition + 4, 2);
 
         // Write the VP8X chunk if necessary.
-        if (updateVp8x)
+        if (updateVp8X)
         {
             long position = stream.Position;
 
-            stream.Position = sizePosition + 12;
-            vp8x.WriteTo(stream);
+            stream.Position = initPosition + 12;
+            vp8X.WriteTo(stream);
             stream.Position = position;
         }
     }

src/ImageSharp/Formats/Webp/RiffOrListChunkHeader.cs

@@ -0,0 +1,26 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+
+namespace SixLabors.ImageSharp.Formats.Webp;
+
+internal readonly struct RiffOrListChunkHeader
+{
+    public const int HeaderSize = 12;
+
+    public readonly uint FourCc;
+
+    public readonly uint Size;
+
+    public readonly uint FormType;
+
+    public ReadOnlySpan<byte> FourCcBytes => MemoryMarshal.CreateReadOnlySpan(ref Unsafe.As<uint, byte>(ref Unsafe.AsRef(in this.FourCc)), sizeof(uint));
+
+    public bool IsRiff => this.FourCc is 0x52_49_46_46; // "RIFF"
+
+    public bool IsList => this.FourCc is 0x4C_49_53_54; // "LIST"
+
+    public static ref RiffOrListChunkHeader Parse(ReadOnlySpan<byte> data) => ref Unsafe.As<byte, RiffOrListChunkHeader>(ref MemoryMarshal.GetReference(data));
+}

src/ImageSharp/Formats/Webp/WebpConstants.cs

@@ -28,6 +28,11 @@ internal static class WebpConstants
         0x2A
     ];
 
+    /// <summary>
+    /// Gets the header bytes identifying a Webp.
+    /// </summary>
+    public const uint WebpFourCc = 0x57_45_42_50;
+
     /// <summary>
     /// Signature byte which identifies a VP8L header.
     /// </summary>
@@ -55,11 +60,6 @@ internal static class WebpConstants
         0x50 // P
     ];
 
-    /// <summary>
-    /// The header bytes identifying a Webp.
-    /// </summary>
-    public const string WebpFourCc = "WEBP";
-
     /// <summary>
     /// 3 bits reserved for version.
     /// </summary>
@@ -319,4 +319,9 @@ internal static class WebpConstants
         -7, 8,
         -8, -9
     ];
+
+    /// <summary>
+    /// Gets the header bytes identifying a Webp.
+    /// </summary>
+    public static ReadOnlySpan<byte> WebpFormTypeFourCc => "WEBP"u8;
 }

src/ImageSharp/Formats/Webp/WebpImageFormatDetector.cs

@@ -11,7 +11,7 @@ namespace SixLabors.ImageSharp.Formats.Webp;
 public sealed class WebpImageFormatDetector : IImageFormatDetector
 {
     /// <inheritdoc />
-    public int HeaderSize => 12;
+    public int HeaderSize => RiffOrListChunkHeader.HeaderSize;
 
     /// <inheritdoc />
     public bool TryDetectFormat(ReadOnlySpan<byte> header, [NotNullWhen(true)] out IImageFormat? format)
@@ -21,21 +21,9 @@ public sealed class WebpImageFormatDetector : IImageFormatDetector
     }
 
     private bool IsSupportedFileFormat(ReadOnlySpan<byte> header)
-        => header.Length >= this.HeaderSize && IsRiffContainer(header) && IsWebpFile(header);
-
-    /// <summary>
-    /// Checks, if the header starts with a valid RIFF FourCC.
-    /// </summary>
-    /// <param name="header">The header bytes.</param>
-    /// <returns>True, if its a valid RIFF FourCC.</returns>
-    private static bool IsRiffContainer(ReadOnlySpan<byte> header)
-        => header[..4].SequenceEqual(WebpConstants.RiffFourCc);
-
-    /// <summary>
-    /// Checks if 'WEBP' is present in the header.
-    /// </summary>
-    /// <param name="header">The header bytes.</param>
-    /// <returns>True, if its a webp file.</returns>
-    private static bool IsWebpFile(ReadOnlySpan<byte> header)
-        => header.Slice(8, 4).SequenceEqual(WebpConstants.WebpHeader);
+        => header.Length >= this.HeaderSize && RiffOrListChunkHeader.Parse(header) is
+        {
+            IsRiff: true,
+            FormType: WebpConstants.WebpFourCc
+        };
 }

src/ImageSharp/Formats/_Generated/ImageMetadataExtensions.cs

@@ -14,6 +14,7 @@ using SixLabors.ImageSharp.Formats.Qoi;
 using SixLabors.ImageSharp.Formats.Tga;
 using SixLabors.ImageSharp.Formats.Tiff;
 using SixLabors.ImageSharp.Formats.Webp;
+using SixLabors.ImageSharp.Formats.Ani;
 
 namespace SixLabors.ImageSharp;
 
@@ -102,6 +103,26 @@ public static class ImageMetadataExtensions
     /// <returns>The new <see cref="IcoMetadata"/></returns>
     public static IcoMetadata CloneIcoMetadata(this ImageMetadata source) => source.CloneFormatMetadata(IcoFormat.Instance);
 
+    /// <summary>
+    /// Gets the <see cref="AniMetadata"/> from <paramref name="source"/>.<br/>
+    /// If none is found, an instance is created either by conversion from the decoded image format metadata
+    /// or the requested format default constructor.
+    /// This instance will be added to the metadata for future requests.
+    /// </summary>
+    /// <param name="source">The image metadata.</param>
+    /// <returns>
+    /// The <see cref="AniMetadata"/>
+    /// </returns>
+    public static AniMetadata GetAniMetadata(this ImageMetadata source) => source.GetFormatMetadata(AniFormat.Instance);
+
+    /// <summary>
+    /// Creates a new cloned instance of <see cref="IcoMetadata"/> from the <paramref name="source"/>.
+    /// The instance is created via <see cref="GetIcoMetadata(ImageMetadata)"/>
+    /// </summary>
+    /// <param name="source">The image metadata.</param>
+    /// <returns>The new <see cref="IcoMetadata"/></returns>
+    public static AniMetadata CloneAniMetadata(this ImageMetadata source) => source.CloneFormatMetadata(AniFormat.Instance);
+
     /// <summary>
     /// Gets the <see cref="JpegMetadata"/> from <paramref name="source"/>.<br/>
     /// If none is found, an instance is created either by conversion from the decoded image format metadata
@@ -283,6 +304,26 @@ public static class ImageMetadataExtensions
     /// <returns>The new <see cref="IcoFrameMetadata"/></returns>
     public static IcoFrameMetadata CloneIcoMetadata(this ImageFrameMetadata source) => source.CloneFormatMetadata(IcoFormat.Instance);
 
+    /// <summary>
+    /// Gets the <see cref="AniFrameMetadata"/> from <paramref name="source"/>.<br/>
+    /// If none is found, an instance is created either by conversion from the decoded image format metadata
+    /// or the requested format default constructor.
+    /// This instance will be added to the metadata for future requests.
+    /// </summary>
+    /// <param name="source">The image frame metadata.</param>
+    /// <returns>
+    /// The <see cref="IcoFrameMetadata"/>
+    /// </returns>
+    public static AniFrameMetadata GetAniMetadata(this ImageFrameMetadata source) => source.GetFormatMetadata(AniFormat.Instance);
+
+    /// <summary>
+    /// Creates a new cloned instance of <see cref="IcoMetadata"/> from the <paramref name="source"/>.
+    /// The instance is created via <see cref="GetAniMetadata(ImageFrameMetadata)"/>
+    /// </summary>
+    /// <param name="source">The image frame metadata.</param>
+    /// <returns>The new <see cref="IcoFrameMetadata"/></returns>
+    public static AniFrameMetadata CloneAniMetadata(this ImageFrameMetadata source) => source.CloneFormatMetadata(AniFormat.Instance);
+
     /// <summary>
     /// Gets the <see cref="GifFrameMetadata"/> from <paramref name="source"/>.<br/>
     /// If none is found, an instance is created either by conversion from the decoded image format metadata

src/ImageSharp/IO/BufferedReadStream.cs

@@ -3,6 +3,7 @@
 
 using System.Buffers;
 using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
 
 namespace SixLabors.ImageSharp.IO;
 
@@ -22,10 +23,14 @@ internal sealed class BufferedReadStream : Stream
 
     private readonly unsafe byte* pinnedReadBuffer;
 
-    // Index within our buffer, not reader position.
+    /// <summary>
+    /// Index within our buffer, not reader position.
+    /// </summary>
     private int readBufferIndex;
 
-    // Matches what the stream position would be without buffering
+    /// <summary>
+    /// Matches what the stream position would be without buffering
+    /// </summary>
     private long readerPosition;
 
     private bool isDisposed;
@@ -194,6 +199,49 @@ internal sealed class BufferedReadStream : Stream
         return this.ReadToBufferViaCopyFast(buffer);
     }
 
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public bool TryReadUnmanaged<T>(out T result)
+        where T : unmanaged
+    {
+        this.cancellationToken.ThrowIfCancellationRequested();
+
+        int size = Unsafe.SizeOf<T>();
+
+        if (size > this.BufferSize)
+        {
+            Span<byte> span = stackalloc byte[size];
+            if (this.ReadToBufferDirectSlow(span) != size)
+            {
+                result = default;
+                return false;
+            }
+
+            result = MemoryMarshal.Read<T>(span);
+        }
+        else
+        {
+            if ((uint)this.readBufferIndex > (uint)(this.BufferSize - size))
+            {
+                this.FillReadBuffer();
+            }
+
+            if (this.GetCopyCount(size) != size)
+            {
+                this.EofHitCount++;
+                result = default;
+                return false;
+            }
+
+            Span<byte> span = this.readBuffer.AsSpan(this.readBufferIndex, size);
+
+            this.readerPosition += size;
+            this.readBufferIndex += size;
+            result = MemoryMarshal.Read<T>(span);
+        }
+
+        return true;
+    }
+
     /// <inheritdoc/>
     public override void Flush()
     {

tests/ImageSharp.Tests/Formats/Ani/AniDecoderTests.cs

@@ -0,0 +1,22 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using SixLabors.ImageSharp.Formats.Ani;
+using SixLabors.ImageSharp.PixelFormats;
+using static SixLabors.ImageSharp.Tests.TestImages.Ani;
+
+namespace SixLabors.ImageSharp.Tests.Formats.Ani;
+
+[Trait("format", "Ani")]
+[ValidateDisposedMemoryAllocations]
+public class AniDecoderTests
+{
+    [Theory]
+    [WithFile(Work, PixelTypes.Rgba32)]
+    [WithFile(MultiFramesInEveryIconChunk, PixelTypes.Rgba32)]
+    [WithFile(Help, PixelTypes.Rgba32)]
+    public void AniDecoder_Decode(TestImageProvider<Rgba32> provider)
+    {
+        using Image<Rgba32> image = provider.GetImage(AniDecoder.Instance);
+    }
+}

tests/ImageSharp.Tests/TestImages.cs

@@ -1379,4 +1379,11 @@ public static class TestImages
         public const string CurReal = "Icon/cur_real.cur";
         public const string CurFake = "Icon/cur_fake.ico";
     }
+
+    public static class Ani
+    {
+        public const string Work = "Ani/Work.ani";
+        public const string MultiFramesInEveryIconChunk = "Ani/aero_busy.ani";
+        public const string Help = "Ani/Help.ani";
+    }
 }

tests/Images/Input/Ani/Help.ani

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:c49cbb1ca0a3f268695a80df93b1ce2b2cba335a80e8244dd3a702863159bd99
+size 12998

tests/Images/Input/Ani/Work.ani

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:740353739d3763addddd383614d125918781b8879f7c1ad3c770162a3e143a33
+size 1150338

tests/Images/Input/Ani/aero_busy.ani

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:ff38afb523490e1a9f157c0447bc616b19c22df88bdb45c163243d834e9745f8
+size 556304