Create an animated gif file from images in iOS

gistfile1.m

#import <UIKit/UIKit.h>
#import <ImageIO/ImageIO.h>
#import <MobileCoreServices/MobileCoreServices.h>

- (void)exportAnimatedGif
{
    UIImage *shacho = [UIImage imageNamed:@"shacho.png"];
    UIImage *bucho = [UIImage imageNamed:@"bucho.jpeg"];
    
    NSString *path = [[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject] stringByAppendingPathComponent:@"animated.gif"];
    CGImageDestinationRef destination = CGImageDestinationCreateWithURL((CFURLRef)[NSURL fileURLWithPath:path],
                                                                        kUTTypeGIF,
                                                                        2,
                                                                        NULL);
    
    NSDictionary *frameProperties = [NSDictionary dictionaryWithObject:[NSDictionary dictionaryWithObject:[NSNumber numberWithInt:2] forKey:(NSString *)kCGImagePropertyGIFDelayTime]
                                                                                                   forKey:(NSString *)kCGImagePropertyGIFDictionary];
    NSDictionary *gifProperties = [NSDictionary dictionaryWithObject:[NSDictionary dictionaryWithObject:[NSNumber numberWithInt:0] forKey:(NSString *)kCGImagePropertyGIFLoopCount]
                                                              forKey:(NSString *)kCGImagePropertyGIFDictionary];
    
    CGImageDestinationAddImage(destination, shacho.CGImage, (CFDictionaryRef)frameProperties);
    CGImageDestinationAddImage(destination, bucho.CGImage, (CFDictionaryRef)frameProperties);
    CGImageDestinationSetProperties(destination, (CFDictionaryRef)gifProperties);
    CGImageDestinationFinalize(destination);
    CFRelease(destination);
    NSLog(@"animated GIF file created at %@", path);
}

• (void)exportAnimatedGif
  {
  //Completely in memory approach. Have to be careful with this as it *WILL crash the app and maybe phone if too much
  //is loaded into memory. source: https://gist.github.com/akisute/1141953

  int count = [images count] -1;
  NSString *path = [[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject] stringByAppendingPathComponent:@"animated5.gif"];
  CGImageDestinationRef destination = CGImageDestinationCreateWithURL((__bridge CFURLRef)[NSURL fileURLWithPath:path],
  kUTTypeGIF,
  count,
  NULL);

  NSDictionary *frameProperties = [NSDictionary dictionaryWithObject:
  [NSDictionary dictionaryWithObject: [NSNumber numberWithFloat:0.0] forKey:(NSString *)kCGImagePropertyGIFDelayTime]
  forKey:(NSString *)kCGImagePropertyGIFDictionary];
  NSDictionary *gifProperties = [NSDictionary dictionaryWithObject:
  [NSDictionary dictionaryWithObject: [NSNumber numberWithInt:0] forKey:(NSString *)kCGImagePropertyGIFLoopCount]
  forKey:(NSString *)kCGImagePropertyGIFDictionary];

  for(int i = 1; i < [images count]; i ++){
  int j = [images count] - i;
  UIImage *img = [images objectAtIndex:j];
  CGImageDestinationAddImage(destination, img.CGImage, (__bridge CFDictionaryRef)frameProperties);
  }

  CGImageDestinationSetProperties(destination, (__bridge CFDictionaryRef)gifProperties);
  CGImageDestinationFinalize(destination);
  CFRelease(destination);
  NSLog(@"animated GIF file created at %@", path);
  }

Any luck with getting an acceptable frame rate? Mine is incredibly slow, and looping is dodgy as well? Is there a way to set dither settings etc?

made an adaptation for swift 2 and NSImage: https://gist.github.com/ScottBuchanan/c63129cc2c5bb824fbac21c2d389ed22

I have a problem with this piece of code, when I use this snippet to generate one gif with two static image, it works fine. But when I use ffmpeg to transform this gif to mp4, this mp4 file has a problem that one image is at beginning position and another is at the end. So when I loop this video, it acts strange.
this is my gif