AI LipSync replaces the lip movements in a video with mouth shapes driven by a new audio track, frame by frame. Upload a video containing a visible face and the target audio, and the tool outputs a result video that preserves the original facial expressions, head movement, and background scene while the mouth follows the new speech. Common uses include video dubbing, multilingual localization, and social media content with custom voiceovers.
What to do when video and audio lengths don't match
When the source video and target audio have different durations, you choose a sync strategy:
- Cut off: The shorter length wins; excess is discarded
- Loop: The video loops to cover the full audio length
- Bounce: The video plays forward then reverse, useful for footage with no clear start/end
- Silence: After the audio ends, the video continues with no sound
- Remap: The video frame rate is stretched or compressed to match the audio duration
When the length difference exceeds a 2:1 ratio, loop-based strategies produce noticeably repetitive results. In those cases, trim the source footage to a similar length before processing.
How source video quality affects results
The larger, more front-facing, and clearer the face in the frame, the more natural the lip mapping. These conditions noticeably degrade quality:
- Heavy side angle (over 45°): lip contour and depth estimation become inaccurate
- Mouth obstructed by a hand, microphone, or mask — if you use a Sync model, enable occlusion detection so the object is preserved naturally in the output
- Motion blur or low frame rate: frame-by-frame lip mapping loses its reference points
- Multi-person footage: enable active speaker detection and the model will attempt to lock onto the person currently speaking
Single-person footage, front-facing, well-lit, consistently produces the most stable results. For multi-person scenes, crop to a single-person clip before processing.
PixVerse LipSync
- Faster processing
- Good for social media drafts and quick previews
- No advanced parameters
Sync lipsync 2 / Sync Pro
- Sync strategy, creativity, occlusion detection, active speaker detection
- Sync Pro for high-accuracy professional dubbing
- Billed per second of audio — rate varies by model
Why audio quality matters
Lip shapes are driven by the phoneme sequence in the audio. Background music and ambient noise interfere with phoneme detection, causing lip shapes that don't match the speech content. Clean single-voice audio with minimal reverb produces the most stable results. Audio mixed with background music should be processed through a vocal separation tool before upload.