Why videos break - and what can actually be fixed
An MP4 or MOV file is a chain of "boxes": ftyp (the file type), moov (the index that tells players where every frame is) and mdat (the actual footage). Most "corrupt" videos have perfectly healthy footage - it is the structure around it that is damaged. The three common faults:
- moov at the end of the file. Cameras write the index last. If a player or browser needs it up front, the video appears broken or won't seek. Fixable: this tool moves the moov to the front and corrects every internal offset (the same repair as the classic "faststart" fix).
- Truncated file. An interrupted download or recording leaves a length header pointing past the end of the file, and strict players refuse the whole file. Fixable: the header is patched to the real size, so everything that exists plays.
- Missing moov. The camera died before writing the index at all. Not fixable in a browser - the index must be rebuilt frame by frame against a healthy reference clip from the same device, which desktop tools like untrunc do. This tool detects the case and tells you, instead of pretending.
The rescue re-encode
Browsers are remarkably tolerant decoders. If your damaged file still plays - even badly - the Rescue re-encode button plays it internally and re-records it with your device's hardware encoder, producing a brand-new, structurally clean file. It is the bluntest tool here, but it rescues files that strict editors and phones reject.
How to repair a video
- Drop the file above. The diagnosis runs instantly and lists every box, its size and position.
- Read the verdicts: green is healthy, yellow is fixable, red is not fixable locally.
- Press whichever repair button lights up, then download the repaired copy. Your original file is never modified.
FAQ
Does this Video Repair tool upload files to a server?
- No. The file structure is read and rewritten entirely in your browser. Nothing is transmitted.
What is the moov atom and why does it matter?
- The moov atom is the MP4 index - it tells players where every frame lives. If it sits at the end of the file, browsers and some players cannot start playback; if it is missing, the video is unplayable. This tool detects both cases and can move a misplaced moov to the front.
Can you fix a video with a missing moov atom?
- Not in a browser - the index must be rebuilt frame by frame using a healthy reference video from the same camera, which desktop tools like untrunc do. This tool tells you honestly when that is the case instead of pretending.
What does Rescue re-encode do?
- If your browser can still decode the video despite the damage, the tool plays it internally and re-records it with your device's hardware encoder, producing a brand-new clean file. It is the most robust fix for files with index damage or trailing garbage.
My download stopped midway - can the file be saved?
- Often, partially. If the index (moov) was stored at the front of the file, this tool can patch the truncated length header so players accept the file and play everything that was downloaded.