iOS 利用视频链接截取播放器封面

.h文件
- (void)getVideoImageWithURL:(NSURL *)videoURL time:(NSTimeInterval)time;

.m文件
- (void)getVideoImageWithURL:(NSURL *)videoURL time:(NSTimeInterval)time {
    
    //先从缓存中找是否有图片
    SDImageCache *cache =  [SDImageCache sharedImageCache];
    UIImage *memoryImage =  [cache imageFromMemoryCacheForKey:videoURL.absoluteString];
    if (memoryImage) {
        self.coverImageView.image = memoryImage;
        return;
    }else{
        UIImage *diskImage =  [cache imageFromDiskCacheForKey:videoURL.absoluteString];
        if (diskImage) {
            self.coverImageView.image = diskImage;
            return;
        }
    }
    
    if (!time) {
        time = 1;
    }
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        AVURLAsset *asset = [[AVURLAsset alloc] initWithURL:videoURL options:nil];
        NSParameterAssert(asset);
        AVAssetImageGenerator *assetImageGenerator =[[AVAssetImageGenerator alloc] initWithAsset:asset];
        assetImageGenerator.appliesPreferredTrackTransform = YES;
        assetImageGenerator.apertureMode = AVAssetImageGeneratorApertureModeEncodedPixels;
        CGImageRef thumbnailImageRef = NULL;
        CFTimeInterval thumbnailImageTime = time;
        NSError *thumbnailImageGenerationError = nil;
        thumbnailImageRef = [assetImageGenerator copyCGImageAtTime:CMTimeMake(thumbnailImageTime, 60)actualTime:NULL error:&thumbnailImageGenerationError];
        if(!thumbnailImageRef)
            NSLog(@"thumbnailImageGenerationError %@",thumbnailImageGenerationError);
        UIImage*thumbnailImage = thumbnailImageRef ? [[UIImage alloc]initWithCGImage: thumbnailImageRef] : nil;
        
        __weak typeof(self) weakSelf = self;
        dispatch_async(dispatch_get_main_queue(), ^{
            SDImageCache *cache =  [SDImageCache sharedImageCache];
            [cache storeImage:thumbnailImage forKey:videoURL.absoluteString completion:^{
                
            }];
            weakSelf.coverImageView.image = thumbnailImage;
        });
        
    });
 
}