i am using **AVAssetImageGenerator** for generating the thumbnail images for video. when i pass local video asset url to generate image it is retuning **nil**.i am using below code to generate image.

```
 NSURL *url = [NSURL fileURLWithPath:filepath];

AVAsset *asset = [AVAsset assetWithURL:url];
AVAssetImageGenerator *imageGenerator = [[AVAssetImageGenerator alloc]initWithAsset:asset];
CMTime time =CMTimeMake(1, 1);

CGImageRef imageRef = [imageGenerator copyCGImageAtTime:time actualTime:NULL error:NULL];
UIImage *thumbnail = [UIImage imageWithCGImage:imageRef];
CGImageRelease(imageRef);

```