If there's one thing I've learned from scoring films, it's that the importance of the interplay between music and moving pictures cannot be overstated. Here's how to choose the right music for your video.
(Beware that some might find some of these clips graphic or disturbing.)
What are you trying to convey with your video? Is it a commercial video trying to sell a product? Is it an inspirational story? Sound has powerful influence on how we perceive the mood of something. Think about whether you want the music to complement or juxtapose the visuals. For example, what makes this scene from "Good Morning, Vietnam" so powerful is the juxtaposition: the images of war don't need help in conveying their horror, so rather than unnecessarily include somber or anxious music, Director Barry Levinson chose "What a Wonderful World." It comments ironically on the scene, arguably doubles its impact beyond that of what any complementing music could, and reinforces the unending positivity of Williams' character.
Try creating an emotional mood board of sorts. Watch your footage several times through and simply write down moods or feelings that come to mind. These will help you in choosing music.
Be careful choosing music with lyrics. First, if you have diegetic dialogue or narration, you don't want words competing with words. Second, lyrics remove a layer of emotional maneuvering by more precisely defining the mood. "Good Morning, Vietnam" took advantage of this as shown above. Scorsese used this in "Goodfellas," with "Then He Kissed Me" (it's also one of the greatest long takes in history):
Pacing, Rhythm, and Tempo
The rate of information, rhythm, and tempo are all things to pay attention to. If the music changes style or has a lot of unexpected turns, so should your video, lest one will seem to evolve at a different rate than the other. Tempo is another important consideration. Take the clip from "Whiplash" below. Notice how in the first 90 seconds, the piece being played features a laid-back tempo and beat, but as soon as J.K. Simmons hurls a chair across the room, the tempo is much faster when he tells Miles Teller to play an example or count:
(Beware there's a fair amount of NSFW language in this clip.)
Viewers can only devote so much total attention to both visuals and sound. If you use busy, hectic music that demands attention, it's going to lessen their ability to process the visuals. You might use this to your advantage to overwhelm the viewer or you might use it to convey anxiety. Take this brilliant example from "Vertigo," in which the entire plot unravels in the first minute of the clip. Jimmy Stewart's character compresses two hours of explanation into a single minute, and Herrmann wisely stays out of the dialogue's way, simply underpinning the speech with sparse, ominous chords, then transitioning beautifully seamlessly into the film's love theme as Stewart simultaneously professes his love for Novak:
"Register" refers to the relative "height" of different blocks of frequencies in music. For example, a piccolo lives in a higher register than a cello. A higher register typically conveys much more energy, intensity, and anxiety. For example, note the shrieking violins from the famous shower scene of "Psycho":
On the other hand, note how "Birdman" Director Alejandro González Iñárritu uses the beginning of the passacaglia from the Ravel Piano Trio, which generally lives in the low-to-middle register of the piano, along with the cello and violin that join later. It's dark, somber, and brooding and contributes to the themes of self-doubt, realization, and regret that arc through this scene without overpowering it:
Be Wary of Distinctive Choices
It's important to consider not only how your music complements the video, but what inherent experiences it conjures in the viewer. For example, you may find the perfect country song, but that genre typically creates very strong opinions in a listener, and you don't want opinions of the music to distract from what's happening on screen.
Here's a problem: most songs and other pieces of music have specific, recognizable forms. Something both film scorers and directors have to struggle with is reconciling the form inherent to music and the form inherent to visuals. Take Sia's "Breathe Me." We won't get into music theory, but let's create a simple form diagram of the song (do this for yourself with both music and film):
Intro - A ("Help, I have done it again") - B ("Be my friend") - A' ("Ouch, I have lost myself again) - B' ("Be my friend") - B' - C (Outro)
Now, let's look at how "Six Feet Under" cut the music to fit the series finale.
(Spoiler Alert: This is the final scene of one of the greatest television series of all time. Consider watching the entire series leading up to this if you haven't seen it; it makes the scene so much more powerful.)
Double Intro - A - Variation of B - A' - B' - Variation of B' - Variation of B' - Extended Variation of C
Notice how blocks are shifted around, stretched, shortened, and lyrics are dropped and repeated, with the song's most prominent shift (B'-C) being aligned with the death of one of the central characters, David. Rarely should visual and music form be completely in step (maintain some independence), but the overall timing and important moments should be paid attention to.
Know When to Be Silent
Take it from a musician: you don't always need sound. Take this masterful scene from Hitchcock's "North by Northwest":
What makes the scene so effective? Hitchcock was working with one of the most brilliant film scorers ever (Bernard Herrmann), and yet, there's nary a note for over four minutes. In fact, there's no dialogue for over four minutes either. Why is that? Here's what Hitchcock had to say:
Somebody is going to come along and bump him off. Well of course, this is such a cliché thing, you see, that one has to fight shy of it and run as far away from it as one possibly can, because it’s all predictable. Now, I decide to do something quite different… Let's have it so the audience will have no conception as to how this man is going to be bumped off or shot. So therefore, I take the loneliest, emptiest spot I can so that there is no place to run for cover, no place to hide, and no place for the enemy to hide...
So, this scene is meant to be three things: desolate, desperate, and unpredictable. Desolate means sparse, which means any music can't be overly dense lest it'll compete with the mood. Desperate means it has to convey a feeling of no way out. Unpredictable means the music can't have any real narrative structure that gives away the narrative structure of the scene. What sound is minimal, feels hopeless, and offers no structure? Silence. When does the music finally kick back in? Precisely when the narrative uncertainty is resolved by Cary Grant's character surviving the attack when the plane crashes into the truck. Remember what Mozart said: "The music is not in the notes, but in the silence between." Know when silence can be louder than sound. Music should only be added if it itself adds something. Another great example of this is the crash scene from "Flight," where the diegetic sounds are terrifying enough on their own (there's some language in this clip as well):
Music is an integral part of the experience of moving images, and thus, careful attention should be paid to pairing it with said images. It can make or break a great film.