How to uncorrupt a video file

Fully reversible: the map is broken, the footage isn’t

This is the most common case. The video and audio data are intact, but the file’s index is missing or wrong. That’s typical after a phone app crash, a camera battery dying, or a file with the index at the end that got cut off. Rebuilding the index gets you back a file identical in quality to what you would have had. See the moov atom explained.

Partly reversible: some data is gone

If a download or copy stopped at 70%, you can make the first 70% play, but the rest isn’t in the file. The same goes for clips with bad sectors from a failing card. You get the good parts back and a glitch or a cut where the damage is.

Not reversible

Files that are 0 bytes, all zeros inside, or that were overwritten by new recordings. Also files “recovered” by data-recovery software that actually stitched together fragments from different clips. The software will name it MOV0042.mp4, but the inside is a mess. In those cases, try a different recovery tool on the original card, or a professional lab if it’s important.

How to find out which one you have

Quickest way: open it in our repair tool. The diagnosis is free and you’ll see a 15-second preview if a repair is possible. If you prefer doing it yourself, start with the repair checklist.

What “uncorrupt” really means

People search for how to uncorrupt a video because there is no everyday word for the job. In practice it means one of three things: making a file that won’t open play again, getting rid of glitches in a file that does play, or getting back a video that seems to have disappeared. Each has a different fix, and knowing which one you are dealing with saves a lot of trial and error.

The good news is that the first case, a file that won’t open, is both the most common and the most fixable. In most cases the video and sound inside the file are fine. What broke is a small section that tells players how to read it. Rebuilding that section brings the whole video back, without any loss in quality.

Five quick checks before you try to fix anything

Check the file size. Right-click and look at its properties. A video of several minutes should be tens or hundreds of megabytes. If it shows 0 bytes, there is nothing inside to recover, and you need to find another copy.

Try a different player. Install VLC, which is free and plays almost everything. If VLC plays the video, it isn’t corrupted; your usual player just can’t handle that format.

Try a different device. Copy the file to another computer or phone. If it works there, the problem is on the first device: a missing codec, an outdated app, or a full disk.

Check the extension. Some files are named .mp4 but are really something else, for example a .mov from an iPhone or a .ts from a screen recorder. Players usually look inside the file rather than at the name, but some editors and websites don’t. Renaming won’t fix a corrupted file, but it can fix a mislabeled one.

Check where it came from. If the video was downloaded, sent through a chat app, or synced from the cloud, the original may be fine and only this copy is broken. Download or copy it again before doing anything else.

Things that don’t work (and can make it worse)

Renaming the file to another extension. Changing video.mp4 to video.avi doesn’t change the contents. At best nothing happens; at worst a program tries to treat the file as the wrong format and refuses it.

Free online converters. Most of them can only read what a normal player can read. If the file is missing its index, they fail or produce a few seconds of video and throw the rest away. They also mean uploading your personal footage to an unknown site.

Letting a camera or phone repair the card. When a device says the card needs repairing or formatting, it may truncate or erase files. Say no, take the card out, and copy everything to a computer first.

Recording new videos on the same card or phone storage. New data can overwrite the space where the lost footage lives. Stop using the device until you have a copy.

Running random repair programs from search ads. Some are fine; many are trial versions that only reveal they can’t fix your file after you install them. Prefer tools that show you a preview of the repaired video first.

The easiest fix: let VLC try

VLC has a hidden but useful trick. Open VLC, choose Media, then Convert/Save. Add your broken video, click Convert/Save, pick a profile such as Video H.264 + MP3 (MP4), choose a destination file name, and start. VLC reads as much of the video as it can and writes a fresh copy.

This works for minor damage, such as a file whose header is slightly wrong or whose timing information is confused. It doesn’t work when the file’s index is completely missing, which is the usual situation after a phone or camera shut down while recording. In that case VLC either refuses the file or produces a tiny output.

For AVI files, VLC goes further: when you open a broken AVI it offers to repair the index. Choose to build the index and play, and in many cases the file plays normally from then on within VLC.

The thorough fix: rebuild the index

When a video won’t open anywhere and VLC can’t help, the index is almost always missing. Rebuilding it means scanning the file’s contents, finding each frame of video and chunk of audio, and writing a new index that points at them.

Free tools such as untrunc and FFmpeg can do this, but they need a command line and sometimes a second, healthy video recorded on the same device. Our step-by-step MP4 guide walks through them.

If you’d rather not install anything, the repair page does the rebuild for you. Open the video there, and you’ll see a free 15-second preview of the repaired result. If it looks right, you can unlock the whole file for $9/month or $29/year. If the preview shows it can’t be fixed, you don’t pay.

When the video plays but looks wrong

Grey or green blocks, smeared colours, or frozen frames mean some of the video data itself was damaged. This can happen when a memory card is failing or a file was copied from a damaged drive. The damaged frames can’t be restored, but the rest of the video can usually be saved.

The simplest approach is to trim out the bad section in any video editor and keep the rest. If you need the video to run continuously, re-encoding it (for example by exporting it from an editor) makes the player smooth over the damage. It won’t look perfect at those moments, but it will play through.

If the sound is out of sync, most editors let you nudge the audio track. If it drifts further out of sync over time, the timing information was damaged, and a proper repair that rebuilds timing is the better fix.

When the video has disappeared

If the file is gone rather than broken, you need recovery before repair. Check the recycle bin or trash, recently deleted albums on phones (they keep videos for 30 days), and any cloud backups such as Google Photos, iCloud, or OneDrive.

If it was on a memory card that was formatted or reports errors, free recovery tools like PhotoRec can often find it. Recovered videos frequently come back without their index, so they may need repairing too. Our guide to recovering MP4 files covers this in detail.

Is it ever hopeless?

Sometimes. If the file is empty, full of zeros, or tiny compared with the recording length, the video was never written or has been overwritten. No tool can bring back data that isn’t there.

But hopeless cases are less common than they seem. A file that is the right size but refuses to open is very often fully recoverable. When in doubt, try a repair that shows a free preview. You’ll know within minutes whether your video can be saved.

Uncorrupting a video on Windows, step by step

1. Copy the video to your desktop so you are working on a duplicate.

2. Right-click the copy, choose Properties, and note the size. Anything above a few megabytes is worth trying to fix.

3. Install VLC from videolan.org and try to play the copy. If it plays, you are done: use VLC, or convert the file with VLC’s Convert/Save option for other players.

4. If VLC fails, install the free HEVC Video Extensions from the Microsoft Store (if they’re not free in your region, the version listed for device manufacturers usually is) and try the Photos app. Some phone videos only fail for lack of this codec.

5. If nothing plays it, the file needs repair. Open it on the repair page and check the free 15-second preview, or follow our MP4 repair guide with free tools.

Uncorrupting a video on a Mac

1. Duplicate the file in Finder (Cmd-D) and work on the duplicate.

2. Press space to preview it in Quick Look. If it plays, the file is probably fine and the problem is the app you were using.

3. Try IINA or VLC, both free. QuickTime refuses many formats and slightly imperfect files that other players handle.

4. If the video is in your Photos library, select it and choose File, Export, Export Unmodified Original. Work on that exported file.

5. If no player can open it, repair it. The repair page works in any browser, including Safari.

Uncorrupting a video on iPhone or Android

On a phone, first check that the video has fully downloaded. On iPhone, open Settings, your name, iCloud, Photos, and see whether it is set to optimise storage. Optimised videos are downloaded on demand and may appear broken on a slow connection. Wait on Wi-Fi and try again.

On Android, open the video in a different app: VLC for Android or MX Player handle more formats than most gallery apps.

If it is truly broken, the easiest repair is from a computer, but you can open the repair page directly in the phone’s browser; MP4 and MOV are repaired on the phone itself.

A real example

A parent records a school play on an Android phone. Ten minutes in, the phone overheats and shuts down. Afterwards, the gallery shows a thumbnail but says the video can’t be played. The file is 1.4 GB.

The size tells us the data is there: ten minutes of 1080p at around 17 Mbps is about 1.3 GB. VLC won’t open it. That pattern, right size but won’t open, means a missing index. A rebuild scans the data and writes a new index; the repaired video plays all ten minutes, minus the final second that the phone never saved. Quality is identical to the original because nothing was re-encoded.

Quick answers to common worries

Will I lose the video if a repair fails? No. Repair reads your file and writes a new one. The original stays as it is, so a failed attempt costs nothing.

Is it worth paying for repair? Only if a free preview shows the repair works. Never pay for a tool that can’t show you the result first.

Why was the last bit of my video lost? The device stopped before it could save those final frames. They never reached the file, so no tool can bring them back.

Can I stop it happening again? Mostly. Keep devices charged, leave free storage space, stop recording before switching off, and back up soon after recording.

Signs your video can probably be saved

The file size matches the length of the recording. The video was interrupted rather than deleted. The device that recorded it can still record new videos normally. The file was never opened and re-saved by an editor or converter. If most of these are true, the odds of a full recovery are very good.

What “uncorrupting” really means

There is no switch that marks a file as corrupted. When people say a video is corrupted they usually mean that software tried to read it and found something it did not expect: a missing index, a header pointing to the wrong place, or data that ends before it should. To uncorrupt the video, you rebuild or correct those structures so that players find what they expect.

That is why uncorrupting rarely touches the picture itself. The compressed frames are usually intact, and once the map that describes them is restored, the video plays exactly as it was recorded. Only when the frames themselves are damaged does the result show glitches.