Using webkit's method for determing frame durations of various gif images

SDWebImage/UIImage+GIF.m

@@ -38,8 +38,7 @@
         {
             CGImageRef image = CGImageSourceCreateImageAtIndex(source, i, NULL);
 
-            NSDictionary *frameProperties = CFBridgingRelease(CGImageSourceCopyPropertiesAtIndex(source, i, NULL));
-            duration += [[[frameProperties objectForKey:(NSString*)kCGImagePropertyGIFDictionary] objectForKey:(NSString*)kCGImagePropertyGIFDelayTime] doubleValue];
+            duration += [self frameDurationAtIndex:i source:source];
 
             [images addObject:[UIImage imageWithCGImage:image scale:[UIScreen mainScreen].scale orientation:UIImageOrientationUp]];
 
@@ -59,6 +58,36 @@
     return animatedImage;
 }
 
++ (float)frameDurationAtIndex:(NSUInteger)index source:(CGImageSourceRef)source
+{
+    float frameDuration = 0.1f;
+    CFDictionaryRef cfFrameProperties = CGImageSourceCopyPropertiesAtIndex(source,index,nil);
+    NSDictionary *frameProperties = (__bridge NSDictionary*)cfFrameProperties;
+    NSDictionary *gifProperties = frameProperties[(NSString*)kCGImagePropertyGIFDictionary];
+
+    NSNumber *delayTimeUnclampedProp = gifProperties[(NSString*)kCGImagePropertyGIFUnclampedDelayTime];
+    if(delayTimeUnclampedProp) {
+        frameDuration = [delayTimeUnclampedProp floatValue];
+    } else {
+
+        NSNumber *delayTimeProp = gifProperties[(NSString*)kCGImagePropertyGIFDelayTime];
+        if(delayTimeProp) {
+            frameDuration = [delayTimeProp floatValue];
+        }
+    }
+
+    // Many annoying ads specify a 0 duration to make an image flash as quickly as possible.
+    // We follow Firefox's behavior and use a duration of 100 ms for any frames that specify
+    // a duration of <= 10 ms. See <rdar://problem/7689300> and <http://webkit.org/b/36082>
+    // for more information.
+
+    if (frameDuration < 0.011f)
+        frameDuration = 0.100f;
+
+    CFRelease(cfFrameProperties);
+    return frameDuration;
+}
+
 + (UIImage *)sd_animatedGIFNamed:(NSString *)name
 {
     CGFloat scale = [UIScreen mainScreen].scale;
@@ -108,7 +137,7 @@
     }
     
     CGSize scaledSize = size;
-	CGPoint thumbnailPoint = CGPointZero;
+    CGPoint thumbnailPoint = CGPointZero;
     
     CGFloat widthFactor = size.width / self.size.width;
     CGFloat heightFactor = size.height / self.size.height;
@@ -138,8 +167,8 @@
     }
     
     UIGraphicsEndImageContext();
-	
-	return [UIImage animatedImageWithImages:scaledImages duration:self.duration];
+    
+    return [UIImage animatedImageWithImages:scaledImages duration:self.duration];
 }
 
 @end