Open a damaged or incomplete AVI file in VLC and you may see a dialog that says “Broken or missing AVI Index”. VLC cannot find the file’s index, normally stored in an idx1 chunk at the end of the file. Without that index, the player cannot seek through the video and may show the wrong duration. The dialog gives three choices: “Play as is”, “Don’t play”, and “Build index then play”. Here is what each button does, how to set a default preference, and why VLC’s built‑in fix is only temporary.

What Each Button Does

VLC’s “Broken or missing AVI Index” dialog presents three options. Each one affects your current session differently.

  • Play as is: VLC tries to play the file without any index. You may be able to watch the video, but you cannot seek forward or backward, and the duration shown may be incorrect. Playback may also be unstable if the file is badly damaged.
  • Don’t play: VLC closes the dialog and does not load the file. No index is built, and nothing changes on disk.
  • Build index then play: VLC builds a new index in memory for that playback session only. The index is not written to your file. After you close the file, the original AVI remains unchanged. During playback you can seek normally and the duration should be correct, but the next time you open the same file you will see the dialog again.

How VLC Builds an Index in Memory

The Temporary Index Process

Choose “Build index then play” and VLC reads through the entire AVI file to reconstruct the index in your computer’s RAM. This index is stored only for that playback session. It does not modify the file on disk. The AVI 1.0 index is the idx1 chunk at the end of the file. VLC’s in‑memory index mimics that chunk so the player can seek and show the correct duration while the file is open.

Because the fix is not saved, every time you open the same broken AVI file, VLC must rebuild the index from scratch. This takes time, especially for large files. The original file remains damaged or incomplete.

Setting a Default Preference for the Dialog

To make VLC always handle a broken or missing AVI index a certain way, change a preference. This avoids seeing the dialog each time.

  1. Open VLC and go to Tools > Preferences (on Windows) or VLC > Preferences (on macOS).
  2. Click Input / Codecs in the list on the left.
  3. Look for the setting labeled Damaged or incomplete AVI file.
  4. Choose one of three options:
    • Ask for action (the default): VLC shows the dialog every time.
    • Always fix: VLC automatically builds an index in memory and plays the file, without asking.
    • Never fix: VLC treats the file as if you chose “Play as is”, without asking.
  5. Click Save or Apply to keep your choice.

Changing this preference does not repair the file permanently. It only tells VLC what to do during playback.

Why VLC’s Index Fix is Temporary

VLC’s “Build index then play” option is designed for convenience, not repair. The index is built in memory and never written to the file, so the original AVI remains broken or missing its idx1 chunk. Other media players, video editors, or devices you use later will still see the same problem. The dialog will reappear in VLC the next time you open that file, unless you set the preference to “Always fix”.

For a permanent solution, use a tool that writes a new file with a rebuilt index. That new file will then play correctly in any player, not just VLC.

What a Permanent AVI Index Repair Does

Writing a New Index to Disk

A permanent AVI index repair creates a new AVI file that contains a valid idx1 chunk. The rebuilt index allows any player to seek, show the correct duration, and play the video without errors. The original file is not overwritten; you get a separate, fixed copy. This is different from VLC’s in‑memory fix, which only works during one playback session.

For a permanent fix, process the file with a tool that writes a new index to disk. avi.repair offers an online service that does this.

Checking Whether an AVI Index is Missing

Look for these signs to confirm a broken or missing index:

  • VLC shows the “Broken or missing AVI Index” dialog when you open the file.
  • You cannot seek through the video; the progress bar may not respond.
  • The duration shown is wrong, often much shorter or longer than the actual video.
  • Other media players also fail to play the file or show similar index errors.

These symptoms all point to a missing or corrupted idx1 chunk at the end of the AVI file.