If you synced with iTunes after you took the video and before deleting it, there is software available to extract the video from your computer. Here's an article describing the process. I assume there are more ways, this is the first one I found in a Google search.
If you didn't sync: iDisksoft can recover deleted items directly from the phone. iExplorer (free) should be able to do the same thing if you know where to look (or can browse around). When you delete the video it can be overwritten by new items so recovering quickly is key.
If you can find some way of mounting your whole iPhone directory as an external drive (definitely needs a jailbreak though), you can use normal file recovery softwares to scan for deleted files on the iPhone.