Can you change the auto focus in video mode on a nikon d3100 to manual focus?

I'm thinking of buying a nikon d3100 i was just wondering if you can change af to manual in video mode thanks

Your lens controls your focus so there will be some switches on that, similar to my d3200. Switch the A to the M. This switch is located to side of the lens. When you change that the lens will unlock and you can turn the part right at the end to focus. Then switch to live view and video mode.

The D3100 doesn't allow AF on video.

Get entry level Sony Alpha if you want better control over video. (A57 is discounted at present because the A58 (an upgraded A37 really) has just been launched.