How to repair a corrupted AVI file and rebuild its index

Step by step

1. Copy the file first

   Copy the AVI from the camera card, old drive or download folder to a working folder on another disk. All further steps use the copy, so the original stays available if you want to try something else later.

2. Describe the symptom

   Note what happens in a player. It plays but the progress bar does not move or seeking jumps to the start; the length is zero or far too short; the player warns that the index is broken; or the file does not open at all. Sound with a black picture is often a missing codec rather than damage.

3. Inspect it in Damaged file repair

   Open FileFix Ultimate, choose Damaged file repair and select the copy. The inspection reads the RIFF header, the stream headers and the movi data list, then reports whether idx1 exists, whether it matches the data and whether the declared sizes match the real file length.

4. Run the repair

   If the index is missing or inconsistent, start the repair. The app walks through every audio and video chunk in the movi list, builds a fresh idx1 from what it finds, corrects the RIFF and list sizes and saves the result as a new AVI next to the copy. The copy itself is not changed.

5. Check the repaired file

   Open the new file in your usual player and try seeking to the middle and near the end. If the recording was cut off, the last moments before the cut may be missing or the final frame may look broken. The result shows its validation status so you know whether it passed the structure check.

Why a missing index breaks an AVI

An AVI is a RIFF container. It starts with a header describing the streams, follows with a long movi list where video chunks such as 00dc and audio chunks such as 01wb alternate, and ends with idx1, a table of the position and size of every chunk. Players use that table to seek, to show the length and to keep sound and picture in step.

Cameras, webcams and screen recorders usually write idx1 only when recording stops normally. A dead battery, a crash or a card pulled out too early leaves a file that contains the frames but no table. The same happens to a download or copy that stopped partway. Some players can play such a file from the beginning, but cannot seek, while others refuse it entirely.

What a rebuilt index can and cannot fix

Rebuilding idx1 restores seeking, the correct length and, in most files, normal playback in players that refused the file. It cannot bring back frames that were never written or that were overwritten, so a truncated recording stays shorter than the time you filmed. If the damage is inside the frame data itself, for example a damaged area on a card, the repaired file may still show blocky or frozen moments at those points.

Some players, such as VLC, offer to fix a broken AVI index when opening it, but that fix usually exists only while the file is open. Saving a repaired copy means every player and editor can use it, and you do not need to repeat the step each time.

OpenDML files over 1 GB

The original AVI format reaches its limits at about 1 GB. Larger recordings use the OpenDML extension, often called AVI 2.0, which splits the data into several RIFF segments and uses a different, multi-level index. FileFix Ultimate recognises these files and reports their structure, but does not rewrite them. For such a file, a remux with a tool like ffmpeg, which copies the streams into a new container without re-encoding, is a common alternative; the exact options depend on the file, so test the result before deleting anything.

When it won't work

• Frames that were never written, such as the last seconds of an interrupted recording, cannot be recreated.
• OpenDML AVI files over 1 GB are inspected only; the app does not repair them.
• If the file is mostly zeros or another file's data, which can happen after recovery from a fragmented card, there are no frames to index.
• A codec problem, where sound plays but the picture stays black, is not damage and is solved by a player that supports the codec.

How FileFix Ultimate helps

• Inspects the RIFF structure, stream headers, movi list and idx1, and explains in plain words what is wrong.
• Rebuilds a missing or broken idx1 from the chunks that are really present and corrects the declared sizes.
• Always saves the repaired AVI as a new file; the file you opened is never modified.
• Can first recover deleted AVI files from a card or drive by signature search, then repair the ones whose index was lost.
• Works offline and is free for personal use, without a repair limit.

Frequently asked questions