Audio Out of Sync After Converting? Fix It

Before you try any fix, find out which of two faults you have: sound that is offset by the same amount from the first second to the last, or sound that starts in sync and drifts further behind as the file plays. A constant offset is a container timestamp problem, and a remux or a re-encode usually clears it. Growing drift is almost always a variable frame rate source — a phone screen recording, or a phone camera that changed frame rate when the light did — converted as though its frames were evenly spaced, and it needs a re-encode to a constant frame rate.

On a phone, Convertlix for Android (8.0 or later) does that re-encode on the device: the file is opened through Android's own file picker, the work runs locally, and the result is written to Downloads. Nothing is uploaded and there is no server copy — its network calls carry sign-in, licence, quota and payment traffic, never media. Sign-in is required once, with no guest mode, after which the tools run with the network off. Free-tier videos are capped at 100 MB per file, Premium at 2 GB, and the monthly conversion allowance is server-set and shown in the app.

Constant offset or growing drift? Measure it

You are not imagining this and the file is not cursed. But almost every answer online treats "out of sync" as one problem, and it is two, so half the advice you find is being applied to the wrong fault.

Measuring it takes ninety seconds and is the most useful thing you can do:

1. Play the first thirty seconds. Watch a hard, visible sound — a clap, a door, a consonant on someone's lips — and note roughly how far the audio is from the picture. Anything over about 40 ms is perceptible on speech; 100 ms and up is obvious.
2. Jump to the middle of the file and do it again.
3. Jump to near the end and do it a third time.

Same gap all three times is a constant offset. The audio and video streams are correct; the container says one of them starts at the wrong moment, or an encoder's audio priming delay was not accounted for.

A gap that grows — barely noticeable at 0:30, half a second at 10:00, two seconds at the end — is a timebase mismatch. Something assumed a frame rate the source does not actually keep.

The fixable half is real: both faults have fixes, and the drifting one has a good fix. The half worth conceding is that if the source is already out of sync — a recording app that lost audio samples mid-capture, or a download that was broken before you touched it — converting it re-encodes the fault faithfully. Check the original before blaming the conversion.

What variable frame rate actually does

A constant frame rate video puts a frame every fixed interval: at 30 fps, one every 33.3 ms, forever. A variable frame rate video does not. It stamps each frame with the time it was actually captured, and those intervals move.

Phones produce VFR constantly, for good reasons. Screen recorders emit a frame when the screen changes, so a static screen costs almost nothing. Camera apps drop the capture rate in low light to keep the exposure longer per frame — a clip that reports "30 fps" may have run at 24 in a dim room and 30 outside.

Audio does not work that way. It is a continuous stream of samples at a fixed rate, normally 44,100 or 48,000 per second, and it never drifts.

So the fault appears when a converter reads the average frame rate, decides the file is 30 fps, and rewrites the frames at even 33.3 ms spacing. Every frame really captured 41 ms after the last is now shown 33.3 ms after it, and the error accumulates. A clip whose true average was 27.4 fps written out as 30 fps ends up with picture running about 9 percent fast against sound: by the end of a ten-minute recording that is nearly a minute of separation. That is drift, and it is why long screen recordings are the classic case.

The correct handling is to re-encode with the timestamps honoured, duplicating or dropping frames so a constant output rate still lines up with the original capture times. That is what "convert VFR to CFR" means, and it is a real re-encode: it costs a generation of picture quality and it costs time.

What a phone can fix, and what needs a desktop

Worth being plain about, because this is where most pages overpromise.

A phone handles well: converting a VFR clip to a constant frame rate by re-encoding it, which is the fix for growing drift; rewriting the container to MP4, MKV or MOV, which clears many constant-offset faults that came from an odd source container; and doing it without the file leaving the device.

A desktop genuinely wins at: nudging audio by an exact amount. If you have measured a 220 ms offset, ffmpeg's -itsoffset applies precisely that and copies both streams without re-encoding either — ffmpeg -itsoffset 0.22 -i in.mp4 -i in.mp4 -map 0:v -map 1:a -c copy out.mp4. HandBrake's Video tab has a "Constant Framerate" option with more control over the output rate than a phone tool exposes, and it is the better machine for a 45-minute 4K file regardless. There is no phone equivalent of a millisecond offset box.

If your file plays but will not scrub, that is a different fault with its own cause — the container index rather than the timestamps — covered in Downloaded Video Won't Seek on Your TV? The Fix. And if the sync problem only matters because you wanted the audio anyway, Extract the Audio From a Video on Android skips the picture entirely.

How to fix audio that is out of sync after converting

1. Test the original first. Play the source file and check sync at the start, the middle and the end. If the source drifts too, the conversion did not cause it and a different conversion will not cure it.
2. Classify the fault. Note the gap at three points in the converted file. A steady gap is a constant offset; a growing gap is a frame rate mismatch. This decides everything that follows.
3. Check whether the source is variable frame rate. Screen recordings and clips shot in changing light almost always are. VLC's Tools then Codec Information panel shows the frame rate it has worked out; a value like 27.413 rather than a round 30 is a strong hint.
4. Read the file size. Long-press it in Files. Over 100 MB is above the free per-video ceiling, so trim it first or use Premium, which takes files up to 2 GB.
5. Re-encode from the original for drift. In Convertlix that is Video Converter, which takes MP4, MKV, MOV or AVI, writes MP4, MKV or MOV, and can trim. Always convert from the source, never from the already-drifting output, because a re-encode of a drifting file keeps the drift and adds a generation.
6. Rewrite the container for a constant offset. Converting the file to MP4 again is often enough when the fault came from an unusual source container. If it survives that, the offset is in the source and you need a desktop tool that takes a number in milliseconds.
7. Check the result at three points again. Start, middle, end. Testing only the first ten seconds is how a drifting file gets pronounced fixed.

When this will not work

A source whose audio was recorded with dropped samples is broken at capture, and re-encoding preserves the fault exactly. Files over 100 MB are refused on the free tier, which rules out most long 4K recordings on a free account — a 45-minute 4K clip will not convert at all until you trim it or move to Premium. DRM-protected downloads are encrypted and nothing here opens them. If the audio needs shifting by a specific measured amount, a phone tool cannot do it and a computer running ffmpeg can. And when the same file is in sync on your phone but not on a television, the file is fine: look for the TV's own audio-delay or lip-sync setting, because a soundbar or an audio-processing mode is adding the delay after decoding.

FAQ

Why is my audio out of sync after converting a video?

Two different faults produce that complaint. If the gap is the same at the start, middle and end, the container's timestamps or an encoder's priming delay are wrong, and rewriting the container usually clears it. If the gap grows as the file plays, the source had a variable frame rate and was written out as though it were constant, which needs a re-encode to a constant frame rate.

Why do my screen recordings drift but normal videos do not?

Screen recorders emit a frame only when the screen changes, so the spacing between frames varies enormously — that is variable frame rate. A converter that averages those intervals into a single frame rate misplaces every frame slightly, and the error accumulates over the length of the file. Camera clips shot in changing light do the same thing more mildly, because the capture rate drops to hold a longer exposure.

Does fixing the sync reduce the video quality?

It depends which fault you have. Rewriting the container without re-encoding copies both streams as they are, so the picture is untouched — that fixes constant offsets. Correcting a variable frame rate is a genuine re-encode and costs one generation of quality plus the processing time, because frames have to be duplicated or dropped to land on an even output rate.

How do I shift the audio by an exact number of milliseconds?

That needs a desktop tool. ffmpeg's -itsoffset takes the delay in seconds and copies both streams without re-encoding — for example -itsoffset 0.22 for a 220 ms shift — and video editors expose the same thing as a timeline nudge. A phone converter has no millisecond offset control, so measure the gap first and do this one on a computer.

The video is fine on my phone but out of sync on my TV. Is the file broken?

Probably not. A television, a soundbar or an AV receiver adds its own processing delay after decoding, and picture-enhancement modes are a common source of it. Look for an audio delay, lip-sync or A/V sync setting in the TV's sound menu, and try turning off any motion-smoothing or cinema processing mode. If the file plays in sync on two other devices, the file is not the problem.

Does Convertlix upload my video?

No. The file is opened through Android's own file picker, decoded and re-encoded by the phone itself, and the result is saved to Downloads, so nothing is transmitted and there is no server copy to delete. Its network calls carry sign-in, licence, quota, configuration and payment data only, and it asks for no storage permission. Sign in once, switch on airplane mode, and the conversion still finishes.

---

Measure the gap at the start, the middle and the end before you convert anything again — that one test tells you which of the two faults you have, and Video Converter handles the drifting one on the phone.