An independent filmmaker who is tempted to compose music for his own movie is in luck these days because there are PC-based music scoring software available to help him achieve that omnipotent sensation of being a total auteur of cinema. I mean, you have just written, produced, directed, and edited the darn thing, why not compose the music for the film as well? And if you have to make your movie on the cheap, you might have to rely on open-source and/or free software to get the job done. I've found one freeware, "FL Studio", and one open-source software, "Audacity", to do just that for you. Now, some pros might tell you that these two can only produce amateurish stuff, but you don't want to argue with them, because the fact remains that you simply cannot afford to hire John ("Star Wars") Williams to score the masterpiece you've just shot with the video camera dad gave you for your birthday.
"FL Studio" is a powerful music composition software with a delicious interface. The free version offered online does not have a "save file" function, but to get around that handicap, I've found an open-source beauty called "Audacity" which is capable of recording whatever sound that is produced through the sound card in your computer. So the basic concept is this: use FL Studio to compose the music first, then play it back and save it as an MP3 file using "Audacity".
To download FL Studio, go here, and then grab your copy of "Audacity" here.
Here is an example of a video of mine: "Zen Surfing", done with music composed on FL Studio.