typedef void(^MyImageBlock)(UIImage * _Nullable image);

异步获取视频的第一帧图片

- (void)getThumbnailImage:(NSURL *)videoURL completion:(MyImageBlock)handler {

    dispatch_async(dispatch_get_global_queue(0, 0), ^{

        AVURLAsset *asset = [[AVURLAsset alloc] initWithURL:videoURL options:nil];
        
        AVAssetImageGenerator *generator = [[AVAssetImageGenerator alloc] initWithAsset:asset];
        
        generator.appliesPreferredTrackTransform = YES;
        
        CMTime time = CMTimeMakeWithSeconds(0.0, 600);
        
        NSError *error = nil;
        
        CMTime actualTime;
        
        CGImageRef imageRef = [generator copyCGImageAtTime:time actualTime:&actualTime error:&error];
        
        UIImage *thumb = [[UIImage alloc] initWithCGImage:imageRef];
        
        CGImageRelease(imageRef);
        
        dispatch_async(dispatch_get_main_queue(), ^{
            handler(thumb);
        });
    });
}

异步获取视频的任一帧图片

- (void)getThumbnailImage:(NSURL *)videoURL atTime:(Float64)seconds completion:(MyImageBlock)handler {

    dispatch_async(dispatch_get_global_queue(0, 0), ^{

        AVURLAsset *asset = [[AVURLAsset alloc] initWithURL:videoURL options:nil];
        
        AVAssetImageGenerator *generator = [[AVAssetImageGenerator alloc] initWithAsset:asset];
        
        generator.appliesPreferredTrackTransform = YES;
        generator.requestedTimeToleranceBefore = kCMTimeZero;
        generator.requestedTimeToleranceAfter = kCMTimeZero;
        
        CMTime time = CMTimeMakeWithSeconds(seconds, 600);
        
        NSError *error = nil;
        
        CMTime actualTime;
        
        CGImageRef imageRef = [generator copyCGImageAtTime:time actualTime:&actualTime error:&error];
        
        UIImage *thumb = [[UIImage alloc] initWithCGImage:imageRef];
        
        CGImageRelease(imageRef);
        
        dispatch_async(dispatch_get_main_queue(), ^{
            handler(thumb);
        });
    });
}