In order to voice a particular sound, the mouth needs to be in the appropriate position before any sound is made. In some cases, this causes FaceFX to insert keys at negative times (up to around 300 milliseconds for speech curves and more for gestures). Below are some things to keep in mind with negative keyframes:
- Aggressively Cut Audio - Some games aggressively cut audio so that speech starts right away. Padding audio with some silence can resolve many issues with negative keyframes but this is not always possible so read below for other ways to deal with negative keyframes.
- Use FaceFX to Trigger the Sound - The correct way to deal with negative keyframes is to let FaceFX trigger the sound file at time 0 in the animation. See the FaceFX SDK Documentation for more details. Using FaceFX to trigger sounds can have the side-effect of delaying audio playback slightly. In dialogue sequences this may not be a problem, but action-oriented grunts and groans may require the sound to be played immediately.
- Gesture Curves - Gesture curves can take longer to ramp in than speech target curves. As a result, they can have keys pushed furthest into negative time. One of the analysis actors that ships with FaceFX is called NoNegativeKeys.facefx. This analysis actor prevents gesture curves from activating until time 0.
See AlsoAnalysis Actors