Why an AVI breaks
An AVI keeps its frames in one list, one after another, and writes two things only when the recording ends: the index that says where every frame is (idx1), and the sizes in its header that say how long the file and that list are. When the power cuts out, the card is pulled or the camera crashes, neither gets written. The frames are on the card; the map to them is missing, and many players refuse the file or show nothing.
Some recorders go further and never write the size of each frame either, leaving it to the index that never came. The tool finds each Motion-JPEG frame by its own start and end markers, so those files come back too.
The tool rebuilds the header's sizes and a new index around your frames. It re-encodes nothing, so the picture and the sound are the camera's own, byte for byte. The result is still an AVI.
What we tested it on
We took eight real AVI recordings from FFmpeg's public test collection. We cut seven of them at 85% the way a dead battery would, erased the sizes in their headers, and repaired them; the eighth, from a DV camcorder, was already cut off, a real 1 MB piece of a 1 GB recording. Every frame recorded before the cut came back identical to the original, compared packet by packet. For the recorder that never writes frame sizes, we compared each picture with the ones listed in the recorder's own index.
| Recorded by | Video | Sound | Frames back after the cut |
|---|---|---|---|
| H.264 security recorder | 704×480 H.264 | none | 1,861 of 1,861 |
| Nikon camera | 1280×720 Motion-JPEG | PCM | 99 of 99 |
| Canon camera (OpenDML index) | 1024×768 Motion-JPEG | PCM | 114 of 114 |
| Nikon Coolpix | 640×480 Motion-JPEG | μ-law | 229 of 229 |
| Camera with ADPCM sound | 320×240 Motion-JPEG | IMA ADPCM | 709 of 709 |
| Casio EX-S3 | 320×240 Motion-JPEG | PCM, stored at the end | 254 of 254 |
| Recorder that never writes frame sizes | 640×480 Motion-JPEG | PCM | 42 of 42 |
| DV camcorder, a real 1 MB cut | 720×480 DV | PCM | 8 of 8 |
The sound came back with the picture in every file that had sound, except the Casio clip: it keeps all its sound at the very end of the file, after the picture, so cut short it had no sound left to recover. The camcorder file was cut in the middle of its ninth frame; the tool leaves a torn frame out rather than hand you a broken picture. None of the eight came from a named dash cam brand, but budget dash cams record the same way: Motion-JPEG or H.264 video with PCM or ADPCM sound in an AVI. The check below tells you, for free, whether yours can be rebuilt.
Copy the file before anything else
- Take the card out of the camera, or stop recording. A dash cam on loop recording will write over old clips, including the one you need.
- Copy the AVI to your computer and work on the copy.
- Don't let a phone gallery or an editor "fix" it first. Some of them rewrite the file.
Repair it in your browser
- Open the copy in the checker on this page. Your browser reads the file from your disk and never uploads it.
- Read the result. The checker tells you whether it found the frames and how much of the recording it can rebuild. This step is free.
- Watch the free 5-second preview, if your file is Motion-JPEG. It plays at reduced quality with a watermark and without sound. A browser can't show H.264 video from an AVI, so an H.264 AVI is rebuilt without a preview.
- Download the full video with a paid plan: one video, 3 months or 1 year, and you can cancel anytime. If the repaired video doesn't play, you get a refund.
What VLC's AVI repair does
VLC has an option for this file: Tools > Preferences > Input / Codecs > "Damaged or incomplete AVI file". Set to Always fix, VLC builds an index in memory while it plays. It doesn't save that index, so the file stays broken in every other player, on your phone and in an editor. The tool on this page writes a file that carries its own index.
What it can't bring back
- An AVI whose start is lost, so the header that says what the file holds is gone.
- Recordings over about 1 GB written as several parts (OpenDML): the tool rebuilds the first part, and the result tells you how much of the recording that is.
- TS, MKV and WebM files, which it doesn't open yet.
- GPS, speed and G-sensor data. The repaired file has the picture and the sound only.
- Clips that loop recording has already overwritten, and 0-byte files.
If the checker says it can't rebuild your file, you haven't paid anything.