Hello. My niece is organising my sister's 50th birthday party and has asked if relatives/friends can make a "music" video. Basically singing along to a song karaoke style, dressed up in a silly costume. Can I ....get my son to film me singing along to a song and dancing...then...take the sound off and put the same song over the top so its better sound? If so, is there free downloadable software available to do this? Easy to use as possible please. I have the use of a digital video camera.