Manatee

How to repair a damaged AVI video on macOS

· 6 min read

AVI is a 1990s container that modern macOS barely supports, so the first job is to work out whether your file is damaged or merely unwelcome. If a player built for older formats opens it, the AVI is fine and a conversion to MP4 is the answer. If nothing opens it, the index at the end of the file is probably missing or wrong, and a repair that rebuilds it will usually recover the footage. Either way, the final step is the same: get the video out of AVI.

Why AVI is a special case on a Mac

Apple’s media frameworks read AVI only when the contents are Motion JPEG or a few other old codecs. Most real-world AVIs hold DivX, Xvid, MPEG-4 Part 2, or Cinepak video with MP3 or AC-3 audio, and QuickTime Player reports those as incompatible regardless of their condition.

AVI is also structurally fragile. It is built on RIFF chunks with an index (the idx1 list) that is written at the very end when recording finishes. A camcorder that lost power, a capture card session that crashed, or a download that stopped early leaves a file with all its frames and no index. Older players will sometimes play such a file by scanning it linearly; newer ones refuse.

AVI also had a 2 GB limit in the original specification. Some devices worked around it with an extension (OpenDML), and some did not, which is why long recordings from old hardware sometimes cut off at exactly 2 GB or 4 GB.

Step 1: decide whether it is damaged

  1. Check the size with Command-I. An AVI of 0 bytes, or a few kilobytes, has nothing in it. Look for the original on the camcorder, the tape capture, or the disc it came from.
  2. Open it in a player that supports legacy formats (several free ones exist for macOS). If it plays from start to finish, the file is intact. Skip to the conversion section.
  3. If that player opens it but playback stops at a fixed point, or seeking does not work, the index is damaged. Go to the repair section.
  4. If nothing opens it and the size is plausible, the header or index is missing. Go to the repair section.

Where the file came from matters. Dashcams and older action cameras often record AVI, and their files get corrupted when the card is pulled or the power is cut. Video recorded on a dashcam won’t open on Mac covers the specifics for those devices.

Step 2: repair the AVI

Repairing an AVI means scanning the file for the chunk markers that precede every video and audio frame, rebuilding the list of where each one sits, and writing a new file with a correct index. This is well-understood work, and the Repair mode in Manatee does it.

  1. Copy the AVI to your internal drive if it is on a card, a disc, or an external disk. Work from the copy.
  2. Open Manatee (the first 24 hours include every feature, no card or email required).
  3. Drop the AVI into the window, or right-click it in Finder and choose Fix with Manatee.
  4. Wait for the job to finish. The whole file is read, so a multi-gigabyte capture takes a few minutes.
  5. Read the outcome. Fixed means the rebuilt file plays through. Partial states what was recovered (for example the first forty minutes). Not fixable means no usable frames were found.
  6. Open the repaired copy. It is written alongside the original, which is never modified.

The repair is done entirely on the Mac. Nothing is uploaded, which matters for family footage and for anything from a security or dashboard camera.

Step 3: convert it to MP4

Even a perfect AVI is a liability on a Mac. Quick Look will not preview it, Photos will not import it, and anyone you send it to will need special software. Once the file plays, convert it.

  1. In Manatee, choose Convert.
  2. Drop the repaired AVI in and select MP4 (or MOV for Final Cut Pro and iMovie).
  3. Open the result. The AVI remains where it was.

For AVI, conversion nearly always means re-encoding, because DivX and Xvid cannot be placed in an MP4 container that Apple software will play. Manatee re-encodes to H.264, which plays everywhere. The quality cost at a sensible bitrate is slight, and it is far outweighed by having a file that opens. See How to convert AVI to MP4 on a Mac for more on settings and batch conversion.

What repair cannot do for AVI

  • Footage that was never written. A capture that crashed at minute twelve contains twelve minutes. The repaired file will too.
  • Deleted files. If the AVI was deleted from a card, that is an undelete job, not a repair. Manatee does not recover deleted files.
  • Bad sectors on the source disc. If the AVI lives on an old CD-R or DVD that is degrading, copy it off with a tool that retries bad reads before repairing the copy. The repair can work around gaps but cannot read what the drive cannot deliver.
  • Proprietary codecs. A few capture cards used codecs that nothing modern decodes. The container can be repaired, but the frames inside may still not be viewable without the original software.

Questions

QuickTime offers to convert my AVI. Should I let it? Yes, if the offer appears. That means QuickTime recognizes the codec (usually Motion JPEG from an older camera) and will produce a MOV. If the conversion fails partway, the file is damaged, and a repair is the next step.

The AVI plays but the audio drifts out of sync. Is that corruption? Sometimes. A damaged index can misreport timing so audio and video diverge. Repairing the index often fixes it. If the drift is constant from the start, it is more likely a frame rate mismatch from the original capture, which a converter can correct.

Can I repair an AVI bigger than 4 GB? Yes. The repaired output is written as a modern file without the old size limits. Whether the input contains more than 4 GB of usable data depends on whether the recorder used the OpenDML extension; if it did not, the file probably stopped at the limit.

Is it worth keeping the original AVI after converting? Keep it until you have watched the MP4 through and are satisfied. After that, the MP4 is the better archive copy because it will open on anything.