ios - 获取视频第一桢（异步执行，不会阻塞主线程）

#pragma mark ----------------异步获取视频第一帧---------------------------------
+(void)getVideoImageWithVideoURL:(NSURL *)videoURL atTime:(NSTimeInterval)time result:(void (^)(UIImage* image))block
{
    //先从缓存中查找是否有图片

     
    NSString * key=[[videoURL.absoluteString lastPathComponent] stringByDeletingPathExtension];
    NSString *filePath = [[GlobalFunc getHistoryCachePath:@"FirstImages"] stringByAppendingPathComponent:[NSString stringWithFormat:@"/%@.png",key]];
    UIImage *memoryImage =  [UIImage imageWithContentsOfFile:filePath];
    if (memoryImage)
    {
          block(memoryImage);
           return;
    }
     //如果都不存在，开启异步线程截取对应时间点的画面，转成图片缓存至磁盘
     
         AVURLAsset *asset = [[AVURLAsset alloc] initWithURL:videoURL options:nil];
         AVAssetImageGenerator *assetGen = [[AVAssetImageGenerator alloc] initWithAsset:asset];
         NSMutableArray *times = [NSMutableArray array];
        CMTime inTime = CMTimeMake(1, 25); //第i帧  帧率
             // CMTime inTime=CMTimeMakeWithSeconds(duratuon+i/totalFrames, fps);
        NSValue *timeValue = [NSValue valueWithCMTime:inTime];
        [times addObject:timeValue];
         [assetGen generateCGImagesAsynchronouslyForTimes:times completionHandler:^(CMTime requestedTime, CGImageRef  _Nullable image, CMTime actualTime, AVAssetImageGeneratorResult result, NSError * _Nullable error) {
      
            
             switch (result) {
                 case AVAssetImageGeneratorCancelled:
                     NSLog(@"Cancelled");
                     break;
                 case AVAssetImageGeneratorFailed:
                     NSLog(@"Failed");
                     break;
                 case AVAssetImageGeneratorSucceeded: {
                     NSLog(@"videoURL:%@",videoURL);
                     UIImage *thumbnailImage=[UIImage imageWithCGImage:image];
                     [asset cancelLoading];
                     dispatch_sync(dispatch_get_main_queue(), ^{
                         block(thumbnailImage);
                         NSData *imgData = UIImagePNGRepresentation([UIImage imageWithCGImage:image]);
                         [imgData writeToFile:filePath atomically:YES];
                     });

                     
                 }
                     break;
             }
         }];

}

这个方法多次调用阻塞主线程

// 获取视频第一帧图片
+(UIImage *)getVideoFirstViewImage:(NSURL *)path
{
  
  AVURLAsset *asset = [[AVURLAsset alloc] initWithURL:path options:nil];
  AVAssetImageGenerator *assetGen = [[AVAssetImageGenerator alloc] initWithAsset:asset];
  assetGen.appliesPreferredTrackTransform = YES;
  CMTime time = CMTimeMakeWithSeconds(0.0, 600);
  NSError *error = nil;
  CMTime actualTime;
  CGImageRef image = [assetGen copyCGImageAtTime:time actualTime:&actualTime error:&error];
  UIImage *videoImage = [[UIImage alloc] initWithCGImage:image];
  CGImageRelease(image);
   return videoImage;
}