Throwing not supported exception for animated images

src/ImageSharp/Formats/WebP/WebPDecoderCore.cs

@@ -73,6 +73,10 @@ namespace SixLabors.ImageSharp.Formats.WebP
 
             uint fileSize = this.ReadImageHeader();
             WebPImageInfo imageInfo = this.ReadVp8Info();
+            if (imageInfo.IsAnimation)
+            {
+                WebPThrowHelper.ThrowNotSupportedException("Animations are not supported");
+            }
 
             var image = new Image<TPixel>(this.configuration, imageInfo.Width, imageInfo.Height, this.metadata);
             Buffer2D<TPixel> pixels = image.GetRootFramePixelBuffer();
@@ -195,19 +199,12 @@ namespace SixLabors.ImageSharp.Formats.WebP
             {
                 this.webpMetadata.Animated = true;
 
-                // ANIM chunk will be followed by n ANMF chunks
-                chunkType = this.ReadChunkType();
-                uint animationParameterChunkSize = this.ReadChunkSize();
-                this.currentStream.Skip((int)animationParameterChunkSize);
-                chunkType = this.ReadChunkType();
-
-                // TODO: not sure yet how to determine how many animation chunks there will be.
-                while (chunkType == WebPChunkType.Animation)
-                {
-                    uint animationChunkSize = this.ReadChunkSize();
-                    this.currentStream.Skip((int)animationChunkSize);
-                    chunkType = this.ReadChunkType();
-                }
+                return new WebPImageInfo()
+                       {
+                           Width = width,
+                           Height = height,
+                           IsAnimation = true
+                       };
             }
 
             if (isAlphaPresent)

src/ImageSharp/Formats/WebP/WebPImageInfo.cs

@@ -20,6 +20,11 @@ namespace SixLabors.ImageSharp.Formats.WebP
         /// </summary>
         public bool IsLossLess { get; set; }
 
+        /// <summary>
+        /// Gets or sets whether this image is a animation.
+        /// </summary>
+        public bool IsAnimation { get; set; }
+
         /// <summary>
         /// The bytes of the image payload.
         /// </summary>

src/ImageSharp/Formats/WebP/WebPThrowHelper.cs

@@ -1,6 +1,7 @@
 // Copyright (c) Six Labors and contributors.
 // Licensed under the Apache License, Version 2.0.
 
+using System;
 using System.Runtime.CompilerServices;
 
 namespace SixLabors.ImageSharp.Formats.WebP
@@ -16,5 +17,15 @@ namespace SixLabors.ImageSharp.Formats.WebP
         {
             throw new ImageFormatException(errorMessage);
         }
+
+        /// <summary>
+        /// Cold path optimization for throwing <see cref="NotSupportedException"/>-s
+        /// </summary>
+        /// <param name="errorMessage">The error message for the exception.</param>
+        [MethodImpl(MethodImplOptions.NoInlining)]
+        public static void ThrowNotSupportedException(string errorMessage)
+        {
+            throw new NotSupportedException(errorMessage);
+        }
     }
 }