Finally, I captured it !

السلام عليكم و رحمة الله

Few days ago, I was trying to take a screen shot from an AVI video.
so ..
printScreen button, MS paint, Ctrl + v, some cropping and resizing, save as, ok
Now came the problem. When I opened the saved file I got only a black square instead of the image I captured from the video !
I first thought it was a player problem, so tried different players but still can't get the captured image.
then after some googleing I got this:

Video playing on Windows machine, no matter if it comes from a movie file, Internet, VCD or DVD, can not be captured by regular screen capture methods, because it is usually playing in a hardware overlay. The overlay it almost as if there was another, smaller screen in front of your regular Windows desktop screen. The desktop contains in that place only the so called "overlay key color" - a solid block of color, usually black, blue, magenta or pink, but it can be anything.

How to deal with this problem? There are three methods to capture image from video and game screen:

You can check the three methods here.

and I recommend method 3 if you use a player other than QuickTime, Real or Windows media player. but note that it may slow down your video playing.
Don't know if this works for re-recording other videos playing on the screen or not, haven't tried it, but i think it will.

Happy Screen Shotting! :D