heTranscodeOperation ()
@property (assign, nonatomic) BOOL executing;//判断NSOperation是否执行
@property (assign, nonatomic) BOOL finished;//判断NSOperation是否结束

@property (nonatomic,copy)NSString *diskCachePath;//
@property (nonatomic,copy)NSString *fileName;//沙盒文件名称

@property (nonatomic, copy) DownloaderCancelBlock completedBlock; //下载完成回调block

@end

@implementation HGVideoCacheTranscodeOperation
@synthesize executing = _executing;
@synthesize finished = _finished;

• (instancetype)initWithPath:(NSString *)diskCachePath fileName:(NSString *)fileName completedBlock:(DownloaderCancelBlock)completedBlock{
  self = [super init];
  if (self) {
  _diskCachePath = [diskCachePath copy];
  _fileName = [fileName copy];
  _completedBlock = [completedBlock copy];
  }
  return self;
  }

• (void)start {
  [self willChangeValueForKey:@"isExecuting"];
  _executing = YES;
  [self didChangeValueForKey:@"isExecuting"];

    //判断任务执行前是否取消了任务
  

  if (self.isCancelled) {
  [self done];
  return;
  }
  [self videoTranscodingWithPath:self.diskCachePath fileName:self.fileName completedBlock:self.completedBlock];

}

-(BOOL)isExecuting {
return _executing;
}

• (BOOL)isFinished {
  return _finished;
  }

• (BOOL)isAsynchronous {
  return YES;
  }

//取消任务
-(void)cancel {
@synchronized (self) {
[self done];
}
}
//更新任务状态

• (void)done {
  [super cancel];
  if(_executing) {
  [self willChangeValueForKey:@"isFinished"];
  [self willChangeValueForKey:@"isExecuting"];
  _finished = YES;
  _executing = NO;
  [self didChangeValueForKey:@"isFinished"];
  [self didChangeValueForKey:@"isExecuting"];
  [self reset];
  }

}

//重置请求数据

• (void)reset {
  if (self.completedBlock) {
  self.completedBlock = nil;
  }
  }

pragma mark - 视频转gif -

-(void)videoTranscodingWithPath:(NSString *)diskCachePath fileName:(NSString *)fileName completedBlock:(DownloaderCancelBlock)completedBlock{
NSString *videoPath = [[diskCachePath stringByAppendingPathComponent:fileName] stringByAppendingString:KVideoSuffix];
NSURL *videoURL = [NSURL fileURLWithPath:videoPath];
NSLog(@"存在文件:\n%@",videoURL);

AVURLAsset *asset = [AVURLAsset assetWithURL:videoURL];
AVAssetImageGenerator *generator = [AVAssetImageGenerator assetImageGeneratorWithAsset:asset];
generator.appliesPreferredTrackTransform = YES;
generator.requestedTimeToleranceBefore = kCMTimeZero;
generator.requestedTimeToleranceAfter = kCMTimeZero;

    //视频宽高
AVAssetTrack *videoTrack = [asset tracksWithMediaType:AVMediaTypeVideo].firstObject;
CGSize videoSize = CGSizeApplyAffineTransform(videoTrack.naturalSize, videoTrack.preferredTransform);
videoSize = CGSizeMake(fabs(videoSize.width), fabs(videoSize.height));
generator.maximumSize = videoSize;

NSArray *indexes = [self generateOffsets:asset];
NSLog(@"%li",(unsigned long)[indexes count]);

NSMutableDictionary *images = [NSMutableDictionary dictionaryWithCapacity:[indexes count]];

CMTime actualTime;
for (NSNumber *number in indexes) {
    if (self.isCancelled) {
        [self done];
        return;
    }

    double offset = [number doubleValue];
    NSLog(@"%f",offset);
    if (offset < 0 || offset > CMTimeGetSeconds(asset.duration)) {
        continue;
    }
    CMTime t = CMTimeMakeWithSeconds(offset, (int)[indexes count]);
    NSError *error = nil;
    CGImageRef source = [generator copyCGImageAtTime:t actualTime:nil error:&error];
    if (!source) {
        NSLog(@"Error copying image at index %f: %@", CMTimeGetSeconds(actualTime), [error localizedDescription]);
        return;
    }
    [images setObject:CFBridgingRelease(source) forKey:number];
}
if (self.isCancelled) {
    [self done];
    return;
}
NSMutableArray *strip =[NSMutableArray array];
if (images) {
    NSArray *times = [self generateOffsets:asset];
    for (int idx = 0; idx < [times count]; idx++) {
        NSNumber *time = [times objectAtIndex:idx];
        CGImageRef image = (__bridge CGImageRef)([images objectForKey:time]);
        [strip addObject:[UIImage imageWithCGImage:image]];
        NSLog(@"%d",idx);
    }

        //转码
    @weakify(self)
    [self writeImageAsGIF:strip toPath:videoPath callbackBlock:^{
        @strongify(self)
        self.completedBlock();
        [self done];
    }];
}

}

//时间个数

• (NSArray *) generateOffsets:(AVAsset *)asset{
  double duration = CMTimeGetSeconds(asset.duration);
  NSMutableArray *indexes = [NSMutableArray array];
  double time = 0.0f;
  while (time < duration) {
  [indexes addObject:[NSNumber numberWithDouble:time]];
  time +=0.1;
  }
  return indexes;
  }

///绘制gif
-(void)writeImageAsGIF:(NSArray )images
toPath:(NSString)path
callbackBlock:(dispatch_block_t)callbackBlock {
if ([ [NSFileManager defaultManager] fileExistsAtPath:path]){
[[NSFileManager defaultManager] removeItemAtPath:path error:NULL];
}
path = [path stringByReplacingOccurrencesOfString:KVideoSuffix withString:KGifSuffix];
CGFloat secondsPerFrameFloat = 1 / 30;
NSNumber * secondsPerFrame = [NSNumber numberWithFloat:secondsPerFrameFloat];//30帧

NSDictionary * gifDict = [NSDictionary dictionaryWithObject:secondsPerFrame
                                                     forKey:( NSString *)kCGImagePropertyGIFDelayTime] ;

NSDictionary *prep = [NSDictionary dictionaryWithObject:gifDict
                                                 forKey:(NSString *)kCGImagePropertyGIFDictionary];

NSDictionary *fileProperties = @{
                    (__bridge id)kCGImagePropertyGIFDictionary: @{
                        (__bridge id)kCGImagePropertyGIFLoopCount: @0, // 0 means loop forever
                    }
                };

CFURLRef url = (__bridge CFURLRef)[NSURL fileURLWithPath:path];

CGImageDestinationRef dst = CGImageDestinationCreateWithURL(url, kUTTypeGIF, [images count], nil);
CGImageDestinationSetProperties(dst, (__bridge CFDictionaryRef)fileProperties);

for (int i=0;i<[images count];i++){
    UIImage * anImage = [images objectAtIndex:i];
    CGImageDestinationAddImage(dst, anImage.CGImage,(__bridge CFDictionaryRef)(prep));
}

bool fileSave = CGImageDestinationFinalize(dst);
CFRelease(dst);
if(fileSave) {
    NSLog(@"animated GIF file created at %@", path);
    if ([ [NSFileManager defaultManager] fileExistsAtPath:path]){
        CGFloat gif = [[[NSFileManager defaultManager] attributesOfItemAtPath:path error:nil] fileSize];
        NSLog(@" hehe%lf",gif);
    }
}else{
    NSLog(@"error: no animated GIF file created at %@", path);
}

!callbackBlock?:callbackBlock();

}

@end