Coarticulation

Coarticulation is a fundamental aspect of natural speech that lip sync systems must handle correctly. When humans speak, the mouth does not snap between isolated positions for each sound; instead, it transitions smoothly as the tongue, lips, and jaw prepare for upcoming sounds while still completing the current one.

For example, the mouth shape for "s" differs depending on whether the next sound is "ee" or "oo." AI lip sync models that fail to capture coarticulation produce robotic-looking mouth movements with unnatural transitions. High-quality models learn these contextual dependencies from training data, generating smooth and natural mouth shape sequences.

Coarticulation relates to several other concepts in the AI lip sync pipeline: Viseme , and Phoneme .