AI lip sync takes one still image and an audio track and turns them into a talking video. The model is rarely the reason a result looks off. Most of the problems come from the inputs: the photo, the script and the audio.
This post starts from the symptom. Find the one you're seeing, then fix the input behind it.
Symptom: the mouth barely moves
Likely cause: the face is too small in the frame.
In a wide shot or a group photo, the mouth is only a few dozen pixels across, and the model has very little to work with.
Fix: crop to waist-up or closer, so the face takes up a decent share of the image. Use at least 300 px on each side, and bigger if you have it.
Symptom: teeth or lips look smeared
Likely cause: a blurry or low-resolution source photo.
The model has to invent the inside of the mouth, and it does that badly when the lips themselves are already soft.
Fix: start from a sharper photo. If the tool offers a higher-resolution output tier, try it for close-ups.
Symptom: strange expressions or a stiff face
Likely cause: a full profile, or strong side light that puts half the face in shadow.
Fix: use a face that is turned toward the camera (straight on or slightly angled) and lit evenly. Also check that nothing covers the mouth: hands, microphones, masks and hair all cause trouble.
The face doesn't have to be a real person. Illustrations, 3D characters, mascots and pets work too, as long as there's a clear face with a visible mouth.
Symptom: the face looks frozen between words
Likely cause: a very short or monotone line.
Fix: give the face something to do.
- Write the way people talk, with contractions and short sentences.
- Use commas and full stops for pauses. A face that rests for a beat between sentences reads as more human than one that talks nonstop.
Symptom: the voice and lips disagree on numbers or acronyms
Likely cause: the text-to-speech voice reads "2026" or "GPU" one way, and the lips follow the audio.
Fix: spell things out the way they should be said ("twenty twenty-six", "G P U"), so what you hear and what you see match.
Symptom: lips drift out of sync with uploaded audio
Likely cause: music, background noise or a second voice in the recording. The model tries to animate all of it.
Fix: upload a clean, voice-only take with one speaker. If you want music, add it in the edit afterwards.
Symptom: it looks fine, except at the start or the end
Artifacts tend to show up in the first and last second of a clip. Watch those parts closely. Trimming half a second often saves a take.
A quick review routine
Watch every result once with the sound on, and check three things:
- Hard consonants. The lips should close on "p", "b" and "m".
- The first and last second. This is where artifacts usually appear.
- The eyes. Natural blinking matters as much as the mouth.
Test short, then go long
Test a new photo with a 5–15 second line before you write a full script. Tools usually bill by the second.
For example, the AI lip sync tool in FunGen charges 11 credits per second at 720p and 21 at 1080p, and accepts up to 60 seconds of audio (MP3, WAV or M4A). It shows the cost before it generates.
Eligible new accounts start with 100 free credits. That isn't quite enough for a 10-second 720p clip, which is 110 credits, but it covers a shorter test.
One rule that isn't technical
Only animate photos you have the rights to. Don't make real people say things they didn't say without their permission. That rule heads off most legal and platform problems before they start.
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