What This Tool Does
This tool fixes audio and video synchronization issues by adjusting the audio delay in your video file. If the audio plays too early or too late relative to the video, you can nudge it forward or backward by milliseconds until lips match voices and sound effects line up with action. Processing happens entirely in your browser using WebAssembly.
How It Works
- Upload your video: Select the file from your device. The tool reads the duration and displays it for reference.
- Adjust audio delay: Use the slider to set the delay from -5 seconds (audio plays early) to +5 seconds (audio plays late). Positive values delay the audio; negative values make it start earlier.
- Process and download: The tool applies the audio delay adjustment and outputs a new video file with resynced audio. Download the fixed version immediately.
The adjustment works by shifting the audio timestamp relative to the video stream. No re-encoding of the video itself is needed — just the audio timing gets modified.
When You'd Actually Use This
Podcast video recordings
Recording a video podcast with separate audio and video tracks? External recorders often drift out of sync over long sessions. This tool realigns them before publishing.
Screen recordings with system audio
OBS or QuickTime recordings sometimes have audio lag due to encoding delays. A few hundred milliseconds of adjustment fixes the lip-sync for tutorial videos.
Dual-system filmmaking
Shot video on a camera but recorded audio on a Zoom recorder? Independent recorders rarely stay perfectly synced. Adjust the delay to match clapperboard or hand clap.
Live stream recordings
Live streams often have inherent audio delay from buffering. When downloading and repurposing clips, you can compensate for the lag before editing.
Music performance videos
Filmed a band performance and the audio doesn't match the instruments? Even 100-200ms of misalignment looks obviously wrong. Fine-tune until the timing feels natural.
Conference talk recordings
Venue AV systems sometimes introduce audio latency. When archiving talks, fix the sync so speaker mouth movements match their words.
What to Know Before Using It
Adjustment range is ±5 seconds: The slider goes from -5000ms to +5000ms. If your sync issue is larger than 5 seconds, you may need professional video editing software.
Output is always MP4: Regardless of input format, the output will be an MP4 file. This ensures maximum compatibility across devices and platforms.
Browser memory is the limit: Processing happens entirely in your browser. Files up to 500 MB work well on most modern browsers. Larger files may be slow or fail on low-RAM devices.
Preview before processing: Watch a few seconds of your video to estimate the delay. Clap your hands on camera or note a specific word's lip movement to identify the offset.
Small adjustments matter: Human perception is sensitive to audio-video sync. As little as 40-80ms of misalignment can feel "off" even if you can't pinpoint why.
FAQ
How do I know if audio is early or late?
Watch for lip-sync: if you see mouth movement before hearing the sound, audio is late (use positive delay). If you hear sound before the mouth moves, audio is early (use negative delay).
What's a typical sync offset?
Most consumer recording issues fall in the 100-500ms range. Professional equipment rarely drifts more than 100ms. If your offset is over 1 second, something went fundamentally wrong in recording.
Can this fix drift that gets worse over time?
No — this tool applies a constant delay. If audio starts synced but drifts later over a 30-minute recording (a sample rate mismatch issue), you need professional software that can apply variable time-stretching.
Does this work on iPhone or Android?
Yes, but mobile browsers have stricter memory limits. Videos under 200 MB should work fine on modern devices. Larger files may crash the browser tab on mobile.
What video formats are supported?
Input: MP4, MOV, AVI, MKV, WebM, and most common formats. Output is always MP4 with H.264 video and AAC audio for maximum compatibility.
Can I adjust sync by less than 50ms?
The slider steps in 50ms increments for simplicity. For finer control (like 10-20ms adjustments), you'd need professional video editing software like DaVinci Resolve or Premiere Pro.
Why is my audio still out of sync after fixing?
Double-check your delay direction. Positive delay makes audio play later; negative makes it play earlier. Also verify the offset isn't larger than the ±5 second range this tool supports.