Repair an MP4 file: a quick checklist

The checklist

1. Size. Right-click the file and check its size. Does it make sense for the length you recorded? Roughly, phone 1080p is about 100–130 MB per minute and 4K is 300–400 MB per minute. A file far smaller than that is missing data.

2. First bytes. If you’re comfortable with a hex viewer, an MP4 normally has the letters “ftyp” near the very start. If the start is all zeros, the file was probably recovered from a formatted card and the beginning is gone, which is a much harder case.

3. VLC test. Does it play, play with glitches, show only audio, or show nothing?

4. Where it came from. A copy or download that stopped early means re-fetching. A recording that stopped early (crash, battery) means index rebuild.

5. Do you have another clip from the same camera? If yes, keep it handy. It may be the key to the repair.

Reading the results

Plays in VLC, not elsewhere: easy fix. A lossless remux will almost always do it. See how to fix corrupted MP4 files with free tools.

Plays for a bit and then stops: usually truncated or damaged partway through. You can typically get back everything up to the damage. Our damaged MP4 repair guide covers this.

Won’t open at all, file size looks right: the index is missing. That’s the classic “moov atom not found” case, and it’s very often fixable with a reference clip.

Won’t open, file is tiny or zeros at the start: the data itself is missing. Try recovering the original from the card with recovery software before you try repairing anything.

Repairing it

For the easy cases, FFmpeg does the job for free. For missing indexes, untrunc plus a reference clip does it. If you’d rather not touch a terminal, open the file in our repair tool. It runs the same checks, shows a free preview, and you only pay ($9/month or $29/year, cancel anytime) once the preview actually plays.

When not to bother

Be honest with yourself about what’s on the card. If the file is 0 bytes, or the camera shows it as 00:00 with a size of a few kilobytes, the recording never got saved. No software can fix that, and anyone promising otherwise is guessing.

Repairing MP4s from specific devices

Most MP4 problems look the same on screen, but the cause and the best fix depend a lot on what recorded the file. The notes below cover the sources we see most often. If yours isn’t listed, the closest match by type (phone, action camera, drone, screen recorder) is usually a good guide.

iPhone and iPad

iPhones record HEVC or H.264 in a QuickTime-flavoured MP4 or MOV container, with the index written when you stop recording. The common failure is a recording interrupted by a phone call, a crash of the Camera app, or the phone running out of storage. The file appears in Photos with a duration of zero or won’t open at all.

Files pulled off the phone via AirDrop, iCloud, or a cable are usually complete copies of whatever the phone had. If the phone itself can’t play it, the problem is in the original. If the phone plays it but your computer doesn’t, the problem is usually the transfer: an iCloud download that stopped early, or a Windows machine without an HEVC decoder.

For the second case, install the HEVC extension on Windows or open the file in VLC before assuming it is damaged. For the first case, an index rebuild with another clip shot on the same phone, same resolution and frame rate, gives the best result. Cinematic mode and ProRes clips need a reference in the same mode.

Android phones

Android camera apps vary by manufacturer, but most write H.264 or HEVC video with AAC audio, and most write the index last. Samsung, Pixel, and Xiaomi devices all produce files that rebuild cleanly with a same-phone reference.

A quirk worth knowing: some Android apps write a temporary file with a name like .pending- or a random string while recording, then rename it on stop. If recording was interrupted, the footage may be sitting in that hidden temporary file rather than in your gallery. Connect the phone to a computer, enable hidden files, and look in the DCIM/Camera folder before concluding the clip is gone.

Third-party apps such as Open Camera or messaging apps that record video in-app have their own quirks. Use a reference recorded in the same app, not the stock camera.

GoPro and other action cameras

GoPro cameras split long recordings into chapters of about 4 GB, named GX010001, GX020001, and so on. If the camera shut down mid-recording, only the last chapter is usually broken. Earlier chapters were closed properly and should play.

GoPro files include extra tracks for timecode and telemetry (the GPMF data used for GPS and gyro overlays). A good repair keeps the video and audio tracks; the telemetry track is sometimes lost, which matters only if you rely on stabilisation in GoPro’s own software or on overlays.

GoPro also writes a low-resolution proxy, the .LRV file, alongside each chapter. If the main MP4 is beyond repair, the LRV often survives and gives you at least a watchable version of the moment. It is worth copying off the card along with everything else.

DJI drones and gimbals

DJI drones record to the microSD card in the aircraft. When a drone crashes, loses power, or the card is ejected too early, the last clip is usually missing its index. DJI also caches a lower-quality copy on the phone running the DJI app, so check the app’s cache before anything else.

DJI files rebuild well when you provide a reference clip shot with the same resolution, frame rate, and colour profile (normal, D-Log, or HLG). Mixing profiles can produce a playable file with wrong colours, because the setup data differs.

Dashcams and security cameras

Dashcams record in short loops, typically one to three minutes, and overwrite old loops when the card fills. A crash or a sudden power cut usually damages only the loop that was being written at the time, which is unfortunately the one people most want.

Many dashcams use MP4 with unusual audio formats or proprietary GPS tracks. Rebuilding works best with another loop from the same camera. If the camera supports a protected or event folder, check it too: many cameras copy the event clip there automatically when the G-sensor triggers.

Pull the card out of the camera as soon as you can after an incident. Every minute it stays in, the loop recording is writing over older footage.

Screen recordings, Zoom, and OBS

Screen recorders and meeting apps typically write the file during recording and finalise it at the end. Zoom converts its local recording after the meeting ends; if the conversion is interrupted, you get files with names like double_click_to_convert_01.zoom instead of an MP4. Zoom’s own converter can usually finish the job if you double-click that file with Zoom installed.

OBS writing to MP4 is the classic case of a lost recording after a crash. Since version 30, OBS offers hybrid MP4, which is far more resilient. If you are still on plain MP4, consider switching to MKV or hybrid MP4 and remuxing afterwards. For the file you already lost, an index rebuild with any other recording made at the same OBS settings works well.

Exports from editors

An MP4 that came out of Premiere, Final Cut, DaVinci Resolve, or CapCut and won’t play usually means the export was interrupted or the disk filled up during the export. The easiest fix is to export again. If the project or source media is gone and the export is all you have, treat it like any other truncated recording: rebuild the index from what is there.

If an export plays in the editor’s own preview but not elsewhere, the problem is more likely codec support, for example a 10-bit HEVC export on a machine without hardware decoding, than corruption.

How to tell the repair actually worked

A repaired file that opens isn’t necessarily a good repair. Play it from start to end at normal speed, and jump around the timeline. Watch for frozen frames, green or grey blocks, and audio that slowly drifts out of sync. Check that the duration matches roughly what you expect from the recording.

For a more objective test, run ffmpeg -v error -i repaired.mp4 -f null - and look at the output. A clean file produces nothing or a handful of warnings. Hundreds of decode errors mean parts of the footage are genuinely damaged, and those sections will show artefacts no matter which tool you use.

Also compare the repaired file size with the original. A rebuild should produce a file close to the original size. A much smaller result means the tool stopped early, often at the first damaged region, and you may get more by trying a different approach.

Mistakes that make MP4 repair harder

Running a repair tool directly on the only copy. Some tools write in place. Always work on a copy and keep the original untouched.

Letting the camera or phone “fix” the card. Many devices offer to repair or format a card when they find a damaged file. Repair modes can truncate the file, and formatting removes the directory entry entirely. Decline, remove the card, and copy everything off on a computer first.

Converting before repairing. Uploading a broken file to an online converter or opening it in an editor and exporting it typically keeps only the part the program could read, and throws away the rest permanently. Repair first, convert after.

Using a reference clip with different settings. A 4K 30 fps reference for a 1080p 60 fps broken file gives the rebuild the wrong codec setup, and the result often won’t decode. Match resolution, frame rate, and codec.

Repairing without installing anything

Our repair runs in the browser and on our servers, so there is nothing to install. It tries a lossless remux first, then a native index rebuild that scans the H.264, HEVC, and AAC frames directly, then a reference-based rebuild if you supply a healthy clip. You see which strategy worked in the report.

Open the broken MP4 on the repair page and watch the free 15-second preview. If the picture and sound look right, unlock the full file for $9/month or $29/year. If the preview shows the file can’t be saved, you haven’t paid anything.

What a repair can and can’t bring back

A repair rebuilds the structure around your footage. It can’t invent frames that were never written. If a phone died two seconds into a recording, you will get those two seconds back, not the minute you meant to record. If a card developed bad sectors, the frames stored on those sectors are gone, and the repaired file will show a jump or a smear where they were.

What repair does recover is everything that physically exists in the file: every complete frame, in order, with correct timing, plus the audio that goes with it. In the typical case of a recording that stopped abruptly, that is the whole clip up to the moment of interruption, which is usually almost everything.

Metadata is a partial story. Resolution, frame rate, and codec are always restored because playback needs them. Creation date, GPS location, and camera model may be lost if they lived only in the missing index. Your file manager’s modified date usually survives, and you can copy it back onto the repaired file with touch -r on macOS and Linux or a tool like ExifTool on any platform.

Keeping the repaired file healthy

After a successful repair, make two copies on different drives before you edit or share anything. Video files that were damaged once often came from media that is starting to fail, and the same card can corrupt the next recording too.

Test the card or drive that held the original. On Windows, chkdsk and the free H2testw tool check for errors and fake capacity. On macOS, Disk Utility’s First Aid and F3 serve the same purpose. A card that shows errors should be retired; they are cheap compared with the footage they hold.

For future recordings, keep batteries charged before long takes, avoid removing cards while a camera’s activity light is on, and prefer cards rated for video (V30 or better) in high-bitrate cameras. A card that can’t keep up is a common, quiet cause of corrupted files.

When you are ready, open the file on the repair page, check the free 15-second preview, and unlock the full repair for $9/month or $29/year. Related reading: how to fix corrupted MP4 files and recovering MP4 files.

What a successful MP4 repair looks like

After a good repair you should be able to open the file in any common player, seek to any point in the timeline, and hear audio that stays in sync from start to finish. The duration shown by the player should match roughly how long you recorded. If the duration is much shorter than expected, part of the recording may never have been written to the card, and that portion cannot be rebuilt.

It is worth checking the repaired file in two different players, such as VLC and your system’s default player. Some players are more forgiving than others, and confirming playback in both gives confidence before you delete the broken original or share the result.