How to post video to instagram from laptop?

I do not have it in my Iphone camera roll anymore, although I have it in the "videos" app on my Iphone. But Instagram can't post from there, when I tap upload on Instagram the only choices I have are from camera or from camera roll, not anywhere else on the Iphone. Any help?

You can't from lap top you can do this by mobile only > check website http://www.androidrow.com/