获取视频的某一帧

// 获取视频的某一帧- (UIImage*) getVideoPreViewImageWithVideoPath:(NSURL *)videoPath{    AVURLAsset *asset = [[AVURLAsset alloc] initWithURL:videoPath options:nil];    AVAssetImageGenerator *gen = [[AVAssetImageGenerator alloc] initWithAsset:asset];    gen.appliesPreferredTrackTransform = YES;    gen.requestedTimeToleranceAfter = kCMTimeZero;    gen.requestedTimeToleranceBefore = kCMTimeZero;    CMTime time = CMTimeMakeWithSeconds(0, 1); //当前第0秒第一帧，一秒60帧，当前时间  1/60    NSError *error = nil;    CMTime actualTime;    CGImageRef image = [gen copyCGImageAtTime:time actualTime:&actualTime error:&error];    UIImage *img = [[UIImage alloc] initWithCGImage:image];    CGImageRelease(image);    return img;}