How can I find missing video in my IPhone 4

I just downloaded this application called USB Disk to my IPhone 4 which can transfer various types of file to my IPhone through the application. I transferred a video to my iphone through the application and the size is almost 1 GB, I tried to play the video but it doesnt work, so I click Open with app... on the option but it still doesnt work, so I decided to delete the video on my IPhone, but the capacity still didnt reduce 1 GB even after I deleted & sync the phone with my computer, which means the video is still in the phone even after I deleted it but nowhere to be found, I tried to search everywhere in the phone but still cant find it. Now I just waste 1 GB for nothing, so I want to know how to find the missing video?
Windows XP