First, find out what is wrong
Most videos that "won't play" fall into one of two cases.
| What you see | What it usually means | Free fix? |
|---|---|---|
| Plays on another device or player | The file is fine; the player lacks the codec | Yes: a player such as VLC, or the codec |
| Plays partly, then freezes or jumps | Damage inside the footage | Sometimes: re-saving it with FFmpeg |
| Won't open anywhere, shows 0:00 or "moov atom not found" | The index was never written: the recording stopped early | Untrunc, or the checker on this page |
| 0 bytes | No footage reached the storage | No: there is nothing to repair |
The third case is the common one after a dead battery, a crash or a card pulled out mid-recording. The footage is in the file, but the table that tells a player where each frame sits is missing.
VLC: free, and good for a player problem
VLC plays many files that the built-in player on Windows or a phone refuses, so try it first. If the video plays in VLC, the file isn't broken at all.
VLC also has a repair option, under Tools > Preferences > Input / Codecs > "Damaged or incomplete AVI file". It works on AVI files only. It can't rebuild a missing MP4 or MOV index, and VLC can't play an MP4 whose index is missing.
FFmpeg: free, for files that still have their index
FFmpeg is a free command-line tool. Copying a file's video and sound into a new file often cures a file that plays badly:
ffmpeg -i broken.mp4 -c copy fixed.mp4
If the index is missing, FFmpeg stops with "moov atom not found". It needs the index to know where the frames are, so it can't help with a recording that was cut off.
Untrunc: free, for a missing index
Untrunc is a free, open-source tool made for exactly this case. You give it a working video from the same camera, recorded with the same settings, and the broken one:
untrunc working.mp4 broken.mp4
It writes a repaired copy next to the broken file. It runs from the command line, and depending on your system you may need to download a build or compile it. If you are comfortable with a terminal, it is worth trying.
The checker on this page: a free check, no upload
The checker does the same job as Untrunc, in the browser, with nothing to install:
- Open the broken video. Your browser reads it from your own disk; nothing is uploaded.
- If it asks, add a working video from the same camera. It borrows that video's settings and nothing else.
- The check is free. It tells you whether the footage is there and how much of the recording it can rebuild.
- The 5-second preview is free too, at reduced quality with a watermark, so you can see your footage move before you pay anything.
- Downloading the full video is paid: one video, 3 months or 1 year. If the repaired video doesn't play, you get a refund.
The repair re-encodes nothing: the file holds your camera's own frames and sound inside a new index. We have tested it on real files from GoPro, DJI, 70mai, Tesla and Samsung cameras, and every frame came back identical to the original.
Be careful with "free online" sites
Many sites that offer free online repair upload your video to their server first. If the video is private, that matters. Some also re-encode the result, which costs quality, or only show you the outcome after you pay. Before you upload anything, check the privacy policy and whether you can see a preview first.