Finds the offset for you
Two recordings of the same moment are matched by the shape of their sound, to well under a millisecond on clean audio. One video on its own is checked for claps and hits, and every answer comes with a confidence figure.
Free · runs in your browser
Sync audio and video in your browser
Drop one video to find and fix its audio delay, or drop a video with its separate recordings to line them up by their sound. Check it in slow motion, then save a new file with the picture untouched. Nothing is uploaded.
Why sync your video here
No quality lost
The picture is always copied as it is. When only the timing changes, the sound is copied too and the file is written in seconds. Drift fixes and mixes re-encode the sound alone.
Stays on your device
Videos, recordings, songs and subtitles are processed in this browser tab and never uploaded. Free, with no account and no watermark.
How it works
How to sync audio and video
Drop your files
Drop one video to fix its own sound, or a video together with a separate recording (or several camera clips) to line them up. MP4, MOV, MKV, WebM, WAV, MP3 and M4A all open.
Let it find the offset
Separate recordings are matched by their sound straight away. For a single video press Detect automatically, or Jump to the clap and pick the frame where the hands meet.
Check and fine-tune
Play it back, slow it to ¼× around a clap, and nudge the sound Earlier or Later in 10 ms or 1 ms steps until lips and words meet.
Export video
Press Export video and download the new file. The picture is copied untouched, so nothing is lost and nothing leaves your device.
Four ways to sync
One site for every kind of sync
- Fix audio and video out of sync Work out whether the file or the playback is at fault, then fix the delay or measure it.
- Sync multiple cameras and recorders Two to eight angles and audio recorders lined up by their shared sound, for multicam editing.
- Play a video in sync on several devices A room code, a shared clock and every screen playing the same frame at the same moment.
- Beat sync video maker Clips and photos cut on the beats or bars of your own song, ready in three shapes.
Quick tools
- Test your audio delay A flash and beep, a microphone chirp or tapping: a latency figure in milliseconds.
- BPM finder for songs and videos The tempo of any music file, even one inside a video, with a beat grid to check.
- Tap tempo BPM counter Tap along to any song and read its BPM, with half, double and a check metronome.
- Sync an SRT or VTT subtitle file Shift, stretch or auto-match subtitle timings to the speech, then download the file.
- A digital clapperboard on your phone A free slate with scene, take and a timed flash and crack that syncs cameras and recorders.
Under the hood
How the offset is found
Sound and picture drift apart for two different reasons, and they need different fixes. A fixed offset means every sound arrives the same few milliseconds early or late: a camera that delays its audio, an export setting, a Bluetooth microphone. Drift means the gap grows as the video plays, because two clocks ran at slightly different speeds.
Two recordings of the same moment
When a camera and a separate recorder both heard the room, their waveforms have the same shape at different times. sync.video turns each recording into an outline of its loud attacks, slides one past the other and measures how well they match at every position (cross-correlation, done with fast Fourier transforms in a background worker). The best position is then refined on the raw sound with a method called GCC-PHAT, which ignores differences in microphone colour and level and pins the match to a fraction of a millisecond. The same measurement repeated across the recording shows whether the two clocks drift apart, and by how many parts per million.
One video on its own
With only one file there is nothing to compare the sound against except the picture. Detect automatically scans a stretch of the video at low resolution, notes where the picture changes sharply (hands meeting, a slate closing, a cut) and where the sound has sharp attacks, and finds the delay that lines the two up best. It is honest about how sure it is. When it can’t tell, the clap method is quick: Jump to the clap, step frame by frame to the moment of contact and press This frame is the clap.
Writing the new file
Video files store the time each frame and each slice of sound should play. Moving the sound only changes those times, so sync.video copies the compressed picture and sound into a new file with the sound’s times shifted, and records the shift in the file’s edit list. Nothing is decoded, nothing is lost and a long video is written in seconds. Stretching the sound to cure drift, mixing two recordings or fading music does need the sound to be decoded and encoded again; the picture is still copied.
Guides
Every sync guide
Fix audio sync
- Test your audio delay A flash and beep, a microphone chirp or tapping: a latency figure in milliseconds.
- Fix audio that slowly drifts Two sync points stretch the sound so it stays in step from start to end.
- Sync an SRT or VTT subtitle file Shift, stretch or auto-match subtitle timings to the speech, then download the file.
- Fix Bluetooth headphone delay Reduce the lag of wireless earbuds and speakers, device by device, and measure it.
- Fix audio delay on a TV or soundbar The AV sync setting on Samsung, LG, Sony, Fire TV and Apple TV, and how to measure it.
- Fix streaming audio out of sync One app, one show or every app? Find the cause and the fix for streaming lag.
- Fix Hulu audio out of sync Live TV versus on demand, app resets, audio output and TV sync settings.
- Fix Netflix audio out of sync Netflix’s device checks, audio format changes and your TV’s own sync setting.
- Fix YouTube audio out of sync Browser and app fixes for viewers, and a corrected file for creators before upload.
- Fix audio delay in VLC The J and K keys, Track Synchronization and how to save the delay into the file.
- Set the OBS Sync Offset Measure webcam or capture-card lag from a clap and enter it as the Sync Offset.
- Fix CapCut audio out of sync Slide the audio in the timeline, or correct an exported file without re-editing.
Sync multiple cameras
- A free alternative to PluralEyes What replaced the discontinued sync app, compared honestly, and a browser tool that does the same job.
- Sync a separate mic or recorder to a video Replace a camera’s scratch sound with a lav, recorder or phone recording, lined up automatically.
- Add music or audio to a video Put a song, voiceover or recording on a clip: mix or replace the sound, set the start, fade out.
- Sync audio and video in Premiere Pro Synchronize, Merge Clips and multicam source sequences, plus fixes when Premiere won’t sync.
- Sync audio in DaVinci Resolve Auto Sync Audio, Auto Align Clips and multicam by sound, and what to do when Resolve can’t sync.
- Sync audio in Final Cut Pro and iMovie Synchronize Clips in Final Cut Pro, lining up by hand in iMovie, and a browser shortcut for both.
- A digital clapperboard on your phone A free slate with scene, take and a timed flash and crack that syncs cameras and recorders.
Sync player
- Host a watch party with your own files Friends in different homes, one film, the same moment on every screen.
- Make a video wall from phones, tablets or TVs One picture split over a grid of screens, with gaps for bezels and every tile in step.
- Compare Syncplay, Jellyfin SyncPlay and this Local-file group watching without a desktop player, a media server or a library.
- Host a movie night on Discord Go Live, Watch Together, or a full-quality copy on every screen with Discord for voice.
- Run a silent disco on guests’ phones Headphones on, one room code, and the same beat in every ear without renting a kit.
Beat sync
- BPM finder for songs and videos The tempo of any music file, even one inside a video, with a beat grid to check.
- Tap tempo BPM counter Tap along to any song and read its BPM, with half, double and a check metronome.
- Photo slideshow with music, on the beat Photos that change on the beats of your song, with slow zooms, in three shapes.
- Say the word on beat maker Your own on-beat picture challenge: eight pictures lighting up one per beat.
- Beat sync in CapCut CapCut’s beat markers step by step, and a browser route that cuts on the beat for you.
- Beat markers for Premiere Pro and Resolve Tap markers by hand, or detect every beat and import them into your editor.
Questions about syncing audio and video
Everything runs in your browser, so these answers are about offsets, drift, formats and devices rather than uploads.
How do I fix audio that is out of sync with the video?
Open the video here, find how far out the sound is (Detect automatically, the clap method, or by ear with Earlier and Later), check it in slow motion, then press Export video. The new file has the sound moved by that amount and the picture copied as it was.
Can sync.video find the delay automatically?
Yes, in two ways. When you have two recordings of the same moment (a camera and a separate mic), their waveforms are compared and slid until they match, which is very reliable when both heard the same sounds. For a single video it looks for sharp sounds such as claps and matches them to sudden changes in the picture; that works well with a clap or a slate and less well with talking alone, and it tells you how sure it is.
How do I sync audio from a separate microphone or recorder to my video?
Drop the video and the recording together. They are matched by their sound, so the camera’s own microphone needs to have heard the same thing (its scratch sound is enough). Choose Replace the camera sound and export: you get the camera’s picture with the clean recording in place.
Can I sync several cameras at once, like PluralEyes?
Yes. Add up to eight files at once: cameras and recorders. Each is matched to the first, drift between their clocks is measured, and you can export synced copies or download an FCPXML or Premiere XML timeline with every file already in place.
Why does my audio slowly drift out of sync, and can that be fixed?
Drift happens when the sound and picture were timed by clocks running at slightly different speeds, which is common with separate recorders, long phone recordings and screen captures with a variable frame rate. Set a sync point near the start and one near the end, or let it measure them, and the sound is stretched evenly to stay in step.
Is my video uploaded anywhere?
No. Every file is read and written by your own browser; nothing about it is sent to a server. The only things that ever travel are, in the sync player, small control and clock messages between the devices in a room.
Does syncing re-encode the video or lower its quality?
The picture is never re-encoded: its compressed frames are copied into the new file. When you only move the sound, the sound is copied too. Correcting drift, mixing or fading means the sound is decoded and encoded again (AAC for MP4 and MOV), at a high bitrate.
How precise is it: frames or milliseconds?
Milliseconds. You can move the sound in 1 ms steps, and matching two recordings is precise to a fraction of a millisecond when both are clean. At 30 frames per second one frame is 33 ms, so sync to the frame is easy to reach.
Which file types work?
MP4, MOV, MKV and WebM videos and WAV, MP3, M4A, AAC, FLAC and Ogg sound files open directly in modern browsers. Files the browser can’t read, such as AVI, WMV or camcorder MTS, are converted on your device first.
Does it work on an iPhone or Android phone?
Yes, in a recent Safari or Chrome. Pick the clip from your photos or files, fix it, and use Share to save the result back to Photos. Long 4K files are easier on a computer.
How do I measure my TV’s or Bluetooth headphones’ audio delay?
Open the Audio delay test from the tools. It plays a flash and a beep you can line up by eye, or times a chirp with the microphone, and gives a number in milliseconds that you can type into the TV’s or app’s sync setting.
Can several people play the same video in sync on their own devices?
Yes, with the Sync player. Everyone opens their own copy of the same file, one device starts a room, the others join with its six-character code, and play, pause and seek stay in step. The video itself never leaves each device.
Can it cut my clips or photos to the beat of a song?
Yes. Beat sync finds the tempo and beats of the song, cuts your clips or photos on beats or bars, and exports a 9:16, 1:1 or 16:9 video. The BPM finder and Tap tempo tools help when you just need the number.
Why is the video in sync on my phone but out of sync on my TV?
Then the file is fine and the TV (or its soundbar or Bluetooth speaker) is adding delay to the sound. Measure that delay with the Audio delay test and set the TV’s audio sync or lip-sync setting rather than changing the file.