Lip sync is the precise matching of a character's mouth movements to spoken audio. In AI video generation it comes in two flavors: native speech generation, where the model creates the voice and the matching lip motion together from dialogue you write in the prompt, and audio-driven animation, where you upload a voice recording and the model animates a face to speak it.
How it works
Speech is made of phonemes, and each phoneme maps to a visible mouth shape called a viseme. Modern video models learn this mapping directly from vast amounts of talking footage, so they don't just flap the mouth on the beat — they shape the lips, jaw, and facial muscles to match each syllable, along with natural blinks and head motion. Models with native audio generate the voice track and the frames in a single pass, which keeps timing perfectly aligned.
What it's best at
- Talking-head content — spokesperson clips, UGC-style ads, and product explainers without a camera crew.
- Dialogue scenes — characters that deliver written lines with matching expressions.
- Multilingual delivery — the same character speaking different languages, each with correct mouth shapes.
- Bringing stills to life — a portrait photo that speaks your script.
What a good input includes
Write dialogue in quotation marks inside the prompt and keep lines short — one or two sentences per shot reads most naturally. Name the tone ("warm, conversational") and, for audio-driven generation, use a clean voice recording without background music.