Breathing is not something we are often conscious of, therefore animating a character breathing during dialogue is easily overlooked. Spending the time studying and adding this to your shot can really create a great sense of believability to your work. In fact, as we'll discover, breathing is something that can be used to drive a performance.
We first should take some time to understand how breathing works and what controls it.
Breathing, as I'm sure you're aware, is the expanding and shrinking of the lungs. This is primarily driven by the diaphragm which contracts, moving down and pulling air into your lungs, then during the exhale the diaphragm relaxes, moving up and expelling the air from our lungs. However, this is not the only force acting on the lungs. There are muscles around the ribs which contract, expanding the rib cage by swinging the ribs up, then on the exhale they expand and the ribs swing down causing the rib cage to get smaller.
I've used a 3d animation package to create a graph which represents how lung volume changes during a typical breath taken when at rest. The air fills quickly at first then slows as it reaches the apex, on the exhale, the air leaves the lungs quickly at first then slows as the lung volume reaches it's lowest point.
However when we speak, our breathing pattern is very different. The air is inhaled as before but is then compressed, the muscles around the ribs and the diaphragm working against each other to condense the air in our lungs to create a positive pressure there. The air is then steadily released as the the dialogue is spoken, then after the line of dialogue is finished, the diaphragm is relaxed. This causes the last of the air to empty quickly from the lungs, then we start to breathe in and the process can begin again.
Of course this is not a one way process, dialogue also affects the lung volume - if the dialogue has a particularly loud accent in it, that will affect the lung volume by creating a sudden drop. I've represented this above in my lung volume graph by showing a drop in the curve. As well as loud accents, often 'w' sounds use greater amounts of air and will also cause the above to happen.
Now we have looked at this in abstract, let's look at an example. I've selected a clip of Al Pacino from the start of the teaser trailer for Ocean's 13. Al Pacino's breathing is often quite apparent in his performances. I suspect this is because he was originally a stage actor and has learned how to use and exaggerate his breathing to help to project his voice. But in this case, I believe he's using it primarily to drive tension into his voice.
Ocean's 13 teaser trailer can be found here
"I know people, highly invested in my survival and they are people who really know how to hurt in ways you can't even imagine."
First, let's talk about the performance in general. Al Pacino's character Willy Banks, is a powerful and ruthless casino owner and he has just learned of Danny Ocean's plans to disrupt his business. In this shot, he warns him that there would be violent consequences if Ocean carries out these plans.
Al's character is incensed at the idea that anyone would set out to damage his business, although the conversation is conducted in public, he doesn't want to draw attention to himself. He's also very clever and doesn't want to reveal that he is affected by this. Al Pacino's performance is very restrained, but it's charged with an intensity which leaves us in no doubt that he is deeply enraged. He keeps his face predominately impartial, at only one point does he let the anger he's feeling creep briefly onto his face - just before he says "really know how to hurt". This is known as a 'microexpression', to do this voluntarily, really shows Al Pacino's acting genius, they naturally occur when someone is trying to conceal or repress an emotion. This one flashes across his face, it is literally only there for one frame, hard to spot when the clip is played at full speed but we read it subconsciously.
Microexpression - incandescent rage
There is a wonderfully subtle texture as well as a change in tempo and tone through the piece. During the first line "I know people" his body is ever so slightly loose and there is a hint of a smile that says "you're joking, aren't you?". Then, as he says "highly invested in my survival...", his body tenses, the speed of his delivery increases and we get that glimpse of anger he's feeling, then at "you can't even imagine" his eyes widen and his speech slows down again to intimidate his opponent by suggesting that he could do something crazy.
"I could do something crazy"
Al Pacino's phonemes, like his performance, have been kept small but he's using his breathing to generate as much tension in his voice as possible as well as project what would otherwise be just a whisper. He's forcing as much air as he can through the narrow exit of his voice box. If you watch his throat you can see it tense as he speaks, then relax as he releases the pressure to breathe in.
Here I've animated a representation of his lung volume on the right hand side of the screen. If you would like to step though this video and/or view it at larger size I have placed a quicktime version here
What's interesting is how almost all his movement is initiated or affected by his breathing. You can see his body tensing as he compresses the air before each line of dialogue, then you see his body relax slightly as he inhales. This causes his body to rock backwards a couple of times during this scene. There is only one small body and head movement during "even" that appears to be separate from his breathing.
Here is the animation curve of the bar in the movie above. We can see how the breathing pattern we cited above appears throughout the performance, note the way it varies too. We can also see how the rhythm of his breathing echos the intensity in the performance - at the start during "I know people" his breath is slower, drawing out the exhale in his 'almost laugh', but as his delivery gets more vehement during "highly invested in my survival ... who really know how to hurt" his breathing gets faster, shorter and we find small half-breaths. Then during that intimidating last line, we can see how he slows down again.
So, how can we use this? Well, if you were trying to create a subtle performance and wanted to keep the character still, but not so much that the character 'dies', and obviously we don't want the character just floating around randomly, we could base the character's movements around the breathing and can be sure it will work and add to the performance. Also, if you wanted to create an intensity in your performance you could exaggerate the breathing and seek to show the the tension in the body as the character compresses and holds the air in their lungs as they speak.
Thanks to James Cunliffe who helped me put this post together.