How to take a picture while taking a video with a Nikon D3100?

If I was taking a video, and I thought that I should take a snap of what just happened, how do I take a picture live from the video? Please help me As soon as possible!

Added (1). I'm taking a video of a rugby game and I'd like to take good pictures as well

Added (2). I'm taking a video of a rugby game and I'd like to take good pictures as well

You don't.

There are very few cameras that have that feature. The Nikon 1 series cameras have that ability.

Since you are only using 1 mp (HD video) or 2.2 mp (Full HD video) of the cameras sensor, any still image captured later from the video will be very low resolution when compared to a still image shot using all 14 mp on your cameras sensor.

You can do what some of my videographer colleagues do. The take a still shot of the scene before they start shooting the video and again at the end.

If you are shooting from a script, this process will help you reenact the scene of you find later that one of your takes can't be used for some reason only encountered while you are editing the video (like a contrail in the sky that jumps around between takes)

A Canon EOS-M can do it too. Similar to a Nikon 1. I would imagine similar mirrorless systems can do it too - the fact that these types of camera are mirrorless obviously makes it easier to implement.

All you can really do is to temporarily stop videoing, shoot a still, then go back to videoing.

My canon T3i can photos while taking video but it makes blips in the video and the photos are not spectacular. I think my canon G10 can do that too.

Have you tried hitting the shutter button yet? I didn't know my camera did that until i did hit the shtuter button by mistake! LOl

Page 108 of your manual covers this. Just press the shutter button. Now, you will have to start the video again, but little is lost. Also, you can capture a single frame of video during post processing. See page 113 of your manual.