The file is there. The size looks right — a big file, clearly full of something. But the gallery shows a grey square instead of a thumbnail, the duration reads 0:00, and every player you throw it at says the same thing: this video is corrupt or unsupported.

Before you try anything, it helps to know what actually happened, because almost everything written about "fixing corrupt videos" skips it — and the fix only makes sense once you see the problem.

What actually broke (it's probably not your footage)

An MP4 or MOV file is written in two parts. The video and audio data stream into the file continuously while you record — frame after frame, straight to storage. Then, when recording stops normally, the camera writes a small table at the end: an index that tells any player where every frame starts, how long the video is, and how to decode it.

If the recording never stops normally — a flat battery, an app crash, a memory card pulled mid-write, storage that filled up — that index is never written. The footage is sitting in the file, usually intact. But without the table, a player cannot find the first frame, so it reports the whole file as corrupt.

This is why the broken file is often large and still useless. It is also why the fix is not "recovery" in the usual sense: nothing needs to be un-deleted. The index needs to be rebuilt around the data that is already there.

First, rule out the boring causes

Two minutes of checks before any repair tool:

  • Did the file finish copying? A transfer interrupted halfway produces the same symptoms. If the original still exists on the camera, card, or in a chat app, copy it again and try that copy.
  • Is it actually an MP4? A file renamed from another format will confuse players. The extension should match what recorded it.
  • Try one other player. If the moov index is genuinely missing, no player will save you — but a file with minor damage sometimes plays in one app and not another. Worth one try, not an afternoon.

And one thing not to do: don't install "recover deleted videos" apps for this. Deleted-file recovery is a different problem. Your file is not deleted — it exists and won't open. Recovery scanners will churn through your storage and hand you back the same broken file.

The VLC trick everyone suggests — and its limit

Search this problem and you'll be told to open the file in VLC, which offers to repair it. That advice is half right: VLC has a built-in repair prompt, but it is for AVI files — a different, older container with a different index format. Point VLC at a truncated MP4 and there is no repair offer; it simply fails to play like everything else.

So for MP4 and MOV, the repair has to rebuild the index properly. There are three real ways to do that.

Option 1: fix it on your phone (where the video usually is)

Most broken recordings are born on a phone, a dashcam, a drone, or an action camera — and end up on a phone either way. Video Repair is our Android app built for exactly this failure: it scans the raw data in the damaged file, finds every frame boundary, and writes a fresh index around your original footage.

Three things about how it works are worth knowing before you tap anything:

  • Checking, repairing, and previewing are free. You watch your own footage play inside the app before paying anything. If the recovery is poor, you've lost nothing. A single one-time purchase unlocks saving — no subscription. Current pricing is on the Video Repair page.
  • Nothing is uploaded. The repair runs entirely on the device. For footage you'd rather not send to a stranger's server — family videos, work recordings — that is the whole argument.
  • Nothing is re-encoded. The recovered video is your camera's own data copied through byte for byte, so there is no second round of compression and no quality loss.

It is honest about limits, too: most cameras repeat their picture settings inside the footage itself, so the video usually comes back from the damaged file alone. Sound is the exception — audio settings live only in the missing index, so recovering the audio track needs one healthy clip from the same camera as a reference. The app tells you which case you're in before you start.

Option 2: the open-source route (desktop, command line)

If you're comfortable with a terminal, untrunc is a well-known open-source tool that rebuilds truncated MP4/MOV files. It requires a reference video — a healthy file from the same camera with the same settings — and it runs on your computer, from the command line. No interface, no hand-holding, and results vary by camera, but it's free software doing the same fundamental job: reconstructing the index.

Option 3: desktop repair software

Commercial desktop tools — Stellar Repair for Video being the biggest name — handle a wider spread of formats and batch jobs on Windows and Mac. If your footage lives on a computer and you repair videos regularly, that category is worth a look; we compare it honestly in Stellar Repair for Video alternative, including where the desktop tools win.

What no tool can fix

Being straight about this saves you money and false hope:

  • Overwritten data is gone. If the camera reused that part of storage, or the file was zeroed rather than merely left unindexed, there is nothing to rebuild. A good repair tool tells you this instead of producing a file that opens and plays garbage.
  • Deleted files are a different problem. Repair tools fix files that exist. If the video was deleted, you need recovery, not repair — and the honest advice there is to stop writing to that storage immediately.

Whatever you try: work on a copy. The damaged file is your only source. Any tool worth using reads it without modifying it — Video Repair never writes to the original — but keeping a spare copy costs nothing and protects you from tools that are less careful.

Frequently asked questions

Why does my MP4 show 0:00 length? The duration lives in the index at the end of the file. If recording was interrupted, the index was never written, so players read the length as zero even though the footage data is present.

Will repairing the video reduce its quality? Not if the tool copies the stream through. A proper index rebuild re-wraps your camera's original data without re-encoding it, so the repaired file is pixel-identical to what was recorded.

Do I need a second video from the same camera? Usually not for the picture — most cameras repeat their decode settings inside the footage. You do need one for the sound, and for some formats. A good tool checks your file first and tells you.

Can VLC repair an MP4? VLC's built-in repair prompt covers AVI files. For MP4/MOV the index format is different, and VLC does not offer to fix it.

Is there a free way to check if my video is fixable? Yes — Video Repair checks the file and previews the full repaired result for free on Android; you only pay if you decide to save it. On desktop, untrunc is free but needs a reference file and a command line.

The bottom line

A video that won't play after an interrupted recording is rarely destroyed — it's unindexed. Skip the deleted-file recovery apps, don't burn an hour on the VLC myth, and rebuild the index: on your phone with a tool that shows you the result before charging you, or on a desktop if that's where your footage lives. And keep the original safe until you've watched the repaired copy all the way through.