Animating lip sync can really frighten the beginning animator, and rightly so because it is one of the most difficult techniques for an animator to master. Live-action people have it easy; they just point the cameras at the actors and ask them to speak.
Facial animation is a lot more than just moving the mouth. When a character speaks dialogue, the shape and position of the mouth is perhaps 10–20% of the total effect. Much more important to the audience is the movement of the body and head, as well as the expression in the face and eyes. For the purposes of this article, however, we will start the process with the mouth.
The Eight Basic Mouth Positions
You must first understand how the mouth moves when it speaks. Dozens of different mouth shapes are made during the course of normal speech. Animators usually boil these down to a handful of standard shapes that are used repeatedly. Depending on the style of animation, some animators get away with as few as three or four shapes, and some may use dozens. For most situations, you can get away with approximately eight basic mouth positions. These eight positions usually provide adequate coverage and give you the ability to animate most dialogue effectively.
As Figure 1 shows, Position A is the closed mouth used for consonants made by the lips, specifically the M, B, and P sounds. Typically this can be made by pushing the open jaw pose into negative territory to close the mouth. In this position, the lips are usually their normal width. For added realism, you could mix in an additional shape, to get the lips slightly pursed, for sounds following an "ooo" sound, as in the word room.
Figure 1 Position A is the closed mouth used for consonants made by the lips, specifically the M, B, and P sounds.
Position B, shown in Figure 2, has the mouth open with the teeth closed. This position is a common shape and is used for consonants made within the mouth, specifically sounds made by C, D, G, K, N, R, S, TH, Y, and Z. All these sounds can also be made with the teeth slightly open, particularly in fast speech.
Figure 2 Position B has the mouth open with the teeth closed.
Position C, shown in Figure 3, is used for the wide-open vowels, such as A and I. It is essentially the same as the fundamental shape for an open jaw.
Figure 3 Position C is used for the wide-open vowels, such as A and I.
As Figure 4 shows, Position D is used primarily for the vowel E, but it can also be used on occasion for C, K, or N during fast speech.
Figure 4 Position D is used primarily for the vowel E, but it can also be used for C, K, or N during fast speech.
Position E has the mouth wide open in an elliptical shape, as shown in Figure 5. This is the position used for the vowel O, as in the word flow. It is created by mixing together an open jaw and the "oooh" sound. Sometimes, particularly when the sound is at the end of a word, you can overlap this shape with the one in Position F to close the mouth.
Figure 5 Position E has the mouth wide open in an elliptical shape
Position E is the position used for the vowel O, as in the word flow. Position F, shown in Figure 6, has the mouth smaller but more pursed. Position F is used for the "oooo" sound, as in food, and for the vowel U. It is one of the fundamental mouth shapes.
Figure 6 Position F is used for the "oooo" sound, as in food
Figure 7 shows Position G, which has the mouth wide open with the tongue against the teeth. This position is reserved for the letter L. It can also be used for D or TH sounds, particularly when preceded by A or I. It is essentially an open jaw with the tongue moved up against the top teeth. If the speech is particularly rapid, this shape may not be necessary, and you can substitute Position B.
Figure 7 Position G has the mouth wide open with the tongue against the teeth
Position G is reserved for the letter L. It can also be used for D or TH sounds Position H, shown in Figure 8, has the bottom lip tucked under the teeth to make the sound of the letters F or V. In highly pronounced speech, this shape is necessary, but the shape could also be replaced with Position B for more casual or rapid speech. This shape is one of the extra shapes modeled previously.
Figure 8 Position H has the bottom lip tucked under the teeth to make the sound of the letters F or V.