What to Do When Your Audio and Picture Are Out of Sync in the Edit
The Mouth That Moved Too Early
The cut plays back and something is immediately wrong. A character speaks and the lip movement arrives a fraction before the words. Or a door slam rings out three frames after the door closes. You have sync drift -- and the question is not whether it is fixable. It almost always is. The question is what caused it, because the fix depends entirely on the root cause.
Audio and picture sync errors in the edit fall into four categories, each with a distinct origin and a specific repair method. Misdiagnosing the cause leads to ineffective fixes that appear to work on the current clip but leave the underlying problem intact for every other clip in the timeline. This post covers the diagnostic process for each sync error type, the fix workflow for each, and how to prevent them before they reach the edit.
What Actually Causes Sync Drift
Root Cause 1 -- Sample rate mismatch. Professional audio is recorded at 48 kHz. If a recorder is accidentally set to 44.1 kHz and the NLE imports audio with 48 kHz assumed, the audio plays back at the wrong speed. At 44.1 kHz recorded and 48 kHz playback, audio runs approximately 8.3% slow -- meaning a one-hour recording drifts out of sync by roughly five minutes over its full duration. This is the single most common cause of severe, progressive sync drift.
Root Cause 2 -- Frame rate conflict. Cameras and audio recorders may operate at different frame rates, or the project sequence may be set to a different frame rate than acquisition. A clip shot at 23.976 fps interpreted as 24 fps will drift. A 29.97 fps clip in a 30 fps sequence will drift. The drift accumulates over time and is distinguishable from sample rate mismatch because it is typically smaller in magnitude.
Root Cause 3 -- Timecode break. If a camera or audio recorder experienced a timecode jam-sync failure, a card swap with a timecode reset, or a power cycle during recording, the timecode recorded after the break will not align with the opposing device. Individual clips before the break may be in sync; clips after the break will be offset by a fixed frame count.
Root Cause 4 -- Import offset error. Some NLEs add a fixed offset when importing certain media types, particularly MXF audio from professional recorders or MP4 files from consumer cameras. This produces a constant offset that does not drift -- every clip is off by the same fixed amount.
Three Real-World Sync Scenarios
Scenario 1 -- Corporate interview, Sony FX6 + Sound Devices MixPre-6. The editor notices audio arrives approximately two seconds early by the end of a ten-minute interview. Progressive drift with early audio points to a sample rate mismatch. The MixPre-6 was set to 44.1 kHz on a previous job and never reset. The NLE imported the audio assuming 48 kHz. Fix: re-import the audio files with the correct 44.1 kHz sample rate declared, or use the NLE's clip speed adjustment to retune playback to 44.1/48 = 91.875% speed.
Scenario 2 -- Documentary feature, multiple cameras. Clips from camera A sync correctly; clips from camera B are consistently 5 frames early. The B-camera was shooting at 29.97 fps but the project sequence is 24 fps. The imported clips were interpreted at 24 fps. Fix: in the NLE, right-click the B-camera clips and change the interpret footage frame rate to 29.97. Re-edit the affected clips.
Scenario 3 -- Narrative short, double-system audio. All clips before lunch are in sync. All clips shot after lunch are offset by 14 frames, but the offset is consistent -- not drifting. This is a timecode break. The audio recorder was powered down during the lunch break and restarted without re-jamming timecode to the camera. Fix: manually slip the audio track 14 frames on every post-lunch clip, or use the NLE's "synchronise clips by audio waveform" function if the recorded clapperboard is visible in those clips.
Sync Error Types and Fix Methods
| Error Type | Symptom | Drift Pattern | Primary Fix |
|---|---|---|---|
| Sample rate mismatch | Audio arrives early or late and drifts | Progressive -- grows over time | Re-import with correct sample rate |
| Frame rate conflict | Consistent offset or slow drift | Progressive or constant | Re-interpret clip frame rate in NLE |
| Timecode break | Consistent offset on specific clips | Constant from break point | Manual slip or waveform sync |
| Import offset error | All clips off by same amount | Constant, no drift | NLE import settings / offset correction |
Diagnosing and Fixing Sync: Step by Step
- Check one representative clip first. Pick a clip with a visible sync point -- a clapperboard, a door slam, a hand clap. Play back and measure the offset in frames using your NLE's timecode display. Note whether the audio is early or late relative to picture.
- Test whether the offset is constant or drifts. On the same clip, check sync at the beginning and end. If it is the same number of frames off at both points, you have a constant offset (timecode break or import error). If the offset grows over the clip's duration, you have a rate mismatch.
- For progressive drift, open the audio clip's properties and verify the declared sample rate in the NLE against the sample rate shown in the file's metadata. Use MediaInfo (free, Windows/Mac) to read the actual embedded sample rate. If there is a mismatch, re-import with the correct rate declared.
- For frame rate drift, check the clip's source frame rate in the NLE against the project sequence frame rate. Right-click the affected clip and choose "Interpret Footage" or equivalent to declare the correct frame rate.
- For constant offset, use the NLE's slip tool to slide the audio track the measured frame offset on all affected clips. In Premiere Pro, the "synchronise clips" function matches waveforms and can automate this on a clip-by-clip basis.
- Verify the fix across the full clip, not just the start. A sample rate fix that corrects the start of a clip should also correct the end -- if it does not, the problem is more complex and may involve a variable bitrate audio file.
- Document the root cause in the project notes so the audio department can correct the source problem before additional material arrives from set.
Pro Tips and Common Mistakes
Pro Tip: Before importing any audio from an external recorder, verify the sample rate using MediaInfo or the recorder's own metadata display. Catching a 44.1/48 kHz mismatch at import costs 30 seconds. Catching it after a full assembly edit costs hours.
Pro Tip: For double-system audio workflows, configure your NLE to use audio waveform matching for initial sync rather than relying on timecode alone. Waveform sync catches timecode breaks automatically and is immune to jam-sync failures. Premiere Pro, DaVinci Resolve, and Final Cut Pro all support waveform-based synchronisation. See Timecode in Film Production for how to prevent timecode breaks during production.
Common Mistake: Manually slipping a drifting clip to sync at the midpoint and calling it fixed. A drifting sync error that is corrected at the midpoint will be out of sync at the head and tail. Progressive drift requires a rate correction, not a position correction.
Common Mistake: Assuming sync errors are the audio department's fault before checking the project settings. A correct 48 kHz audio file imported into a sequence configured at the wrong frame rate will show sync errors that are entirely an editorial setting issue. Check your sequence settings before contacting the sound team.
Frequently Asked Questions
How many frames of sync drift are noticeable to an audience?
Research published by the Society of Motion Picture and Television Engineers suggests that most viewers can detect audio-picture sync errors of approximately two frames or more. Lip sync errors specifically -- where audio arrives before picture -- are perceptible at smaller offsets than audio arriving after picture. For broadcast delivery, sync within one frame of the reference picture is standard.
Can I use Adobe Premiere's "Synchronise" function to fix all sync errors automatically?
Waveform synchronisation in Premiere Pro and similar NLEs works reliably for double-system audio where a clear sync point (clapperboard, clap) is present in the recording. It does not correct rate mismatches -- it only aligns the starting position. A drifting sample rate problem will still drift after waveform sync.
What if the audio file has a variable sample rate?
Variable sample rate audio is rare in professional production but can occur with some consumer devices recording in compressed formats (AAC, MP3). Variable rate audio cannot be corrected by a simple rate interpretation and may require re-encoding with a third-party tool at a fixed target rate before use in a professional NLE. For broadcast delivery requirements, see Audio Delivery Standards for Film and Television.
Should the sound team or the editor fix sync errors?
If the root cause is a recording error (wrong sample rate, failed jam-sync), the sound team should be notified so the problem does not recur on future material. The editorial fix is typically the editor's responsibility. For large-scale sync problems affecting hundreds of clips, a specialist post-production supervisor should evaluate whether a systematic fix or a full audio re-conform is the more efficient path.
Related Tools and Posts
For the production-side causes of sync errors, Timecode in Film Production covers jam-sync, timecode formats, and how to configure recorders and cameras so that the edit starts clean. For sample rate selection and its implications for post-production workflows, Sample Rates in Film Audio: 48kHz vs 96kHz explains why 48 kHz is the broadcast standard and when higher sample rates create more problems than they solve. For final delivery requirements that will catch any remaining sync errors before submission, Audio Delivery Standards for Film and Television covers broadcast and streaming specifications.
Diagnosis First, Then Fix
Sync errors in the edit are fixable in almost every case -- but only if you identify the root cause before reaching for the slip tool. A sample rate mismatch needs a rate correction. A timecode break needs a position correction. Applying the wrong fix to the wrong problem produces a timeline that looks correct on one clip and falls apart on the next. Run the diagnostic sequence, identify the cause, apply the right fix, and verify it across the full duration of affected clips.
What is the most unusual sync error you have encountered in the edit, and what turned out to be the root cause?
