Low Res thumbnails

Am I doing something wrong??

I just purchased this, thinking it was some option I had to turn on/off to get the video resizing to work??

But all my thumbnails look very low res? As soon as I click on the video they return to normal, and stay that way when I minimise them….

http://danredding.co.uk/pro-videography/

Thanks

Dan

https://wordpress.org/plugins/gallery-images/