Getting a character's mouth to match the audio is the line between a video that feels real and one that feels slightly off. When it's wrong, viewers don't always articulate why it bothers them, they just click away. When it's right, a dubbed clip or a talking photo reads as natural, increasing the likelihood of a viewer remaining engaged. This guide covers how AI lip sync actually works, the three ways to do it and where it pays off most.
What is AI lip sync?
AI lip sync matches the mouth movements in a video to a separate audio track, so a person or character looks like they're saying the words in that audio. Upload a face and an audio clip, and the model does the rest.
Under the hood, the model breaks speech into phonemes, the distinct sounds that make up words, and maps each one to a viseme, the mouth shape that produces that sound. It then redraws the mouth, jaw and often the teeth and tongue frame by frame so the timing lines up. Better models also shift the rest of the face slightly to mimic natural expression, which is what separates convincing lip sync from the uncanny kind.
Side angles, fast speech and close-up shots are the hard cases because they hide part of the mouth. Fast or overlapping speech is also tough to track. Close-ups expose every artifact on the teeth. The cleaner and more front-facing your source footage, the better the result.
The three ways to lip sync with AI
There are three main approaches to lip syncing, and which one you use depends on what you're starting with.
Prompt to video
Start from nothing but a description. Some text-to-video models can generate a character who appears to be speaking — you write what the character looks like and what they say, and the model produces a clip with mouth movement. This is the right move when you don't have any footage yet and want to create a talking character from scratch. The tradeoff is control: you get less say over the exact performance, and sync quality can vary enough that results often benefit from upscaling.
Audio plus image
Drop in a still photo and an audio clip, and the tool animates the face to speak. This is how you turn a single image into a talking avatar, a spokesperson or a character that reads a line. Runway's Add Dialogue app does exactly this. It's the fastest path when you already have a face and a voice track to drive it.
Performance transfer
You act out the line on camera, and the model transfers your mouth movements, expressions and timing onto a different character or image. Runway's Act-Two is built for this, driving a character's performance from a simple video input so the emotion and timing of a real take carry through. Use this approach when the performance matters as much as the words.
How to make a lip sync video, step by step
- Choose your starting point. Pick a video clip with a visible face, a still photo or a performance you'll record. Front-facing, well lit, with the mouth clearly visible gives the model the most to work with.
- Get clean audio. Record it or generate a voice track. Clear audio with minimal background noise syncs far better than a noisy source material.
- Run a short test first. Upload your inputs, pick the approach that fits, and generate a few seconds before committing to the full clip. It's faster to catch problems on a five-second clip than a five-minute one. If you're new to generating video, make AI videos fast covers the basics, and the AI video prompting guide helps with the prompt-driven approach.
- Refine the result. If the frames look choppy or soft, run the clip through an upscaler or frame interpolation to smooth it out.
- Export and edit. Download the MP4 and drop it into your project.
Where AI lip sync is used
Most guides stop at dubbing. The more interesting uses show up when you think about it as a way to separate a performance from the language, the take or the person delivering it.
| Use case | Industry | Starting point |
|---|---|---|
| Dub a film into multiple languages | Film & media | Existing footage |
| Fix a flubbed line without a reshoot | Film & media | Existing footage |
| Localize a spokesperson ad | Marketing | Existing footage |
| Test multiple scripts with one presenter | Marketing | Existing footage |
| Personalized outreach video at scale | Marketing | Still photo |
| Onboarding or proposal videos | Professional services | Still photo or clip |
| Update training without reshooting | Professional services | Existing footage |
| Deliver instructions in a client's language | Professional services | Existing footage |
Film and media
Dub a short film into five languages while keeping your original cast's faces and performances, so the lead actor still reads as the lead actor in every market. The economics are the draw: AI dubbing can cut localization turnaround by 80 to 90 percent and costs by around 70 percent versus traditional dubbing. Fix a flubbed or rewritten line in post without a reshoot, the way ADR works but for the picture. Bring a storyboard character or a piece of archival footage to life to read temp dialogue while you cut. See more in media and entertainment.
Marketing and advertising
Shoot a spokesperson ad once, then localize it into every market without reshooting, swapping the script and the language while the talent stays on screen. Test five different scripts with the same on-camera presenter to see which message lands before you commit budget. Turn a founder's headshot into a personalized outreach video at scale. More on marketing and advertising.
Professional services
Produce personalized onboarding or proposal videos at scale, the same presenter with the client's name and details swapped in. Update a training or compliance module by changing the audio instead of reshooting the whole thing every time a policy changes. Deliver instructions in a client's own language without hiring a presenter for each one. See professional services.
What to watch for
Profile angles and extreme head turns still trip up most models, very fast or overlapping speech can drift out of sync and close-ups expose artifacts on the teeth and tongue. Low-resolution or poorly lit source footage produces weaker results, so start with the cleanest face you can.
The part that matters most isn't technical. Only lip sync faces and voices you have the right to use, and disclose synthetic or dubbed media where your audience would expect a genuine recording. The technology is good enough to mislead, which is exactly why consent and disclosure are not optional.
Frequently Asked Questions
What AI can I use to lip sync?
Any video model or tool that supports lip sync. In practice that falls into three categories: text-to-video models that generate a talking character from a prompt, talking-photo tools that animate a still image from an audio clip, and performance models like Act-Two that transfer a real performance onto a character. Tools like Runway bring all three together in one place so you can choose the right approach per project.
How much does AI lip sync cost?
It varies, ranging from free to paid options. Many tools offer a free option for short clips, and most charge by video length or by generation for longer or higher-resolution work. Runway is free to start on the free plan, with paid plans for more generations and higher resolution.
Is lip sync AI safe to use?
On the data side: use reputable tools and check how they handle footage you upload. On the ethics side: only sync faces and voices you have permission to use, and disclose synthetic media where viewers would expect a genuine recording. Used with consent, lip sync is a production tool like any other.
How does AI lip sync work technically?
The model breaks speech into phonemes and maps each one to a viseme — the mouth shape that produces that sound — then redraws the mouth, jaw, teeth and tongue frame by frame. Better models also shift facial expression subtly to mimic natural human movement, which is what makes the result look real rather than mechanical.
What gives the best lip sync results?
A front-facing face, even lighting, a clearly visible mouth and clean audio with minimal background noise. Profile angles, fast speech and low-resolution source footage are the most common causes of weak results.
Try lip sync with Runway
The difference between content that lands and content that loses viewers is often smaller than you'd think. A mouth that's a frame off or a jaw that doesn't quite close are all it takes. When lip sync is right, dubbed clips, talking photos and localized ads all read as natural. When it's off, viewers feel it before they can name it.
You can lip sync a video or a photo in Runway, free to start, with the Add Dialogue app.
Related: Make AI videos fast · AI video prompting guide
