No, Scratch does not have video capabilities. However, if you import a GIF, each frame will turn into a costume. You can use that for some animations by looping through each costume at a rapid rate. Other than that though, you can't.
You could try to covert the video to an aniamted GIF image. When you drag that into scratch, it imports every single frame as a costume and you can wrte a script to cycle through them.