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How to uncorrupt an MP4 (yes, it's usually possible)
You have an MP4 that won't play — maybe it shows an error code, maybe it just freezes every player you throw at it. Before you accept that it's gone: in most cases a "corrupt" MP4 still contains all of its footage. Here's the plain-language version of what's wrong and how to fix it.
Quick answer: a corrupt MP4 is usually an unfinished MP4 — the index at the end of the file was never written because a crash, power loss, or bad transfer interrupted it. Free checks (VLC, device self-repair, FFmpeg stream copy) fix the easy cases; a reference-file repair fixes most of the rest by rebuilding the index from a healthy clip with the same settings.
Step 1: make a copy
Whatever you do next, do it to a duplicate. Every failed repair attempt on your only original reduces your options.
Step 2: rule out the fake corruption
- Play it in VLC. If VLC plays a file that Windows won't, it's a codec issue (commonly HEVC), not corruption. Done.
- If it came off a phone or SD card, check the original. A file corrupted during transfer often has a healthy original still on the device — re-copy it with a cable. (If you got error 0xc00d36e5, this is the first thing to check.)
- Let the device try. GoPros, drones, and many cameras attempt self-repair when powered on with the card inserted. iPhones can fix interrupted recordings overnight while charging.
Step 3: understand why "repair" tools keep failing
An interrupted MP4 is missing its moov atom — the index that maps every frame. Tools that need to read the file to fix it (VLC's converter, most one-click repair apps) fail immediately because there's nothing readable to convert. That's why VLC outputs a 1 KB file, and why people report trying five or six repair programs with nothing to show for it.
The pattern to recognize: if multiple tools all produce empty or near-empty output, stop feeding the file to converters. The file needs its index rebuilt, not decoded.
Step 4: rebuild the index with a reference file
The method that works on unreadable MP4s is reference-file repair: a short, healthy clip recorded by the same device with the same settings serves as a structural template, and the repair tool uses it to reconstruct the broken file's index around the intact frames.
- Find or record a healthy clip — same device, same resolution and frame rate. 10 seconds is enough.
- Run both files through a reference-repair tool: untrunc (free, command line) or StreamSalvage (drag-and-drop, free preview).
- Check the output plays through with audio in sync. Expect to lose only the last few seconds before the interruption.
Uncorrupt it on your own PC
Drop the broken MP4 into StreamSalvage. It tries a stream-copy first, then rebuilds the index from a reference clip — and shows you the repaired preview free before you pay $29. Nothing is uploaded.
Download StreamSalvage for WindowsWhen it genuinely can't be fixed
Honesty matters here: if the storage itself failed (bad sectors overwrote the data), if the file was overwritten after deletion, or if almost none of the stream data was ever written (a 26 KB file from a 10-minute recording), no repair tool can conjure the frames back. Corruption of the index is fixable; absence of the data is not.
Frequently asked questions
Can you actually uncorrupt an MP4 file?
Usually, yes — if the file was interrupted (crash, power loss, bad transfer) rather than physically destroyed. The video frames are typically still in the file; what's broken is the index that tells players where they are. Rebuilding that index makes the file playable again.
Why did VLC's repair create a tiny 1 KB file?
VLC's convert/fix features can't parse an MP4 with a missing index, so the conversion outputs almost nothing. VLC's "fix" works mainly on AVI index issues, not MP4 structure — a near-empty output file is the expected failure mode, not proof your footage is gone.
What's the free way to fix a corrupt MP4?
Try in order: play it in VLC (rules out codec issues), let the recording device attempt self-repair, run an FFmpeg stream copy, and try untrunc with a healthy reference clip. StreamSalvage also previews its repair for free — you only pay if the file actually comes back.
Do I need a reference file to uncorrupt an MP4?
For the highest success rate, yes — a short healthy clip from the same device and settings acts as a structural template. If you don't have one, you can usually just record a new 10-second clip with the same settings; that works exactly as well.