Create video thumbnail in laravel 5.5

I am working in a project in laravel and I want to create thumbnail when upload video

I am following this artical

https://packagist.org/packages/pawlox/video-thumbnail

pawlox/video-thumbnail

when I call this

 $thumb = VideoThumbnail::createThumbnail(asset('public/stories/videos/21530251287.mp4'), asset("public/images/"), 'thumb.jpg', 2, 600, 600);

its return

Pawlox\VideoThumbnail\VideoThumbnail Object(
[FFMpeg:protected] => 
[videoObject:protected] => 
[videoURL:protected] => http://localhost/sunbay/yms/public/stories/2/videos/21530251287.mp4
[storageURL:protected] => http://localhost/sunbay/yms/public/images
[thumbName:protected] => thumb.jpg
[fullFile:protected] => http://localhost/sunbay/yms/public/images/thumb.jpg
[height:protected] => 600
[width:protected] => 600
[screenShotTime:protected] => 2 )

but thumb not generated.

Please let me know what wrong I am doing. and how to resolved it.

Thanks in advance.

via Chebli Mohamed