Convert AVI to MP4

Bring a .avi from the old world into one that phones and browsers play. DivX-era video is usually copied straight across; truly ancient codecs re-encode automatically.

The converter is ffmpeg compiled to WebAssembly. It downloads once (30 MB) when you pick your first file, then stays in your browser cache.

Your file is processed by your own browser and never uploaded. The engine itself is a one-time 30 MB download the first time you use it, and after that it comes out of your browser cache.

How to use AVI to MP4

  1. 1Drop your .avi onto the box above, or click to pick one.
  2. 2The tool reads which codecs are inside. Streams MP4 can hold are copied; the rest are re-encoded to H.264 and AAC.
  3. 3Download the .mp4 and check the row label to see which path your file took.

Old container, often perfectly good contents

AVI files mostly come from a specific era: camcorders, early digital cameras and the DivX/XviD encoding scene of the 2000s. The container has aged badly, but the video inside frequently has not. MPEG-4 Part 2 video, which is what DivX and XviD produce, is something today's MP4 can hold natively, and MP3 audio slots in just as well.

That is the quiet trick of this page. Instead of re-encoding twenty-year-old footage and stacking new compression artifacts onto old ones, the tool inspects the file and, whenever possible, simply moves the streams into a modern MP4. The picture stays exactly as it was, and the conversion runs at read speed.

When re-encoding is unavoidable

Some AVIs hold formats from even further back, like Cinepak, Indeo or raw DV. MP4 has no place for these, so the tool re-encodes them to H.264 with AAC audio. It decides this per file, before starting, and labels the row so you know which kind of job you got. Browser re-encoding is slower than real time; for one family-archive file it is fine, for a whole box of tapes a desktop tool will serve you better.

One more honest note: a remux keeps the original codec, and a few very old smart TVs only decode H.264. If your copied MP4 still refuses to play somewhere, that is why, and the video converter page re-encodes it properly.

What comes out

An .mp4 with the same picture whenever the copy path applied, a front-loaded index so playback starts immediately, and your original filename with the new extension. Files up to 500 MB are accepted, batches queue one after another, and nothing leaves your browser at any point, which is exactly the right property for digitised home movies that exist nowhere else.

Frequently asked questions

Will my AVI convert without quality loss?
Very often, yes. The classic AVI of the 2000s holds MPEG-4 video, better known by the encoder names DivX and XviD, plus MP3 audio, and an MP4 can carry both of those unchanged. In that case the streams are copied byte for byte and the conversion is done in seconds. Files with older codecs inside get re-encoded, which the row for that file will say explicitly.
The MP4 downloaded, but my TV still will not play it. Why?
Because the codec inside did not change, only the container did. A device that cannot decode MPEG-4 Part 2 video will refuse it in an MP4 just as it did in an AVI. If that happens, use our video converter page, which can re-encode to H.264, the codec even the most stubborn hardware accepts.
What AVI files will not copy cleanly?
Ones holding formats MP4 has no slot for, like Cinepak or Indeo from the 1990s, or DV video from tape camcorders. These are detected up front and re-encoded automatically. Re-encoding in a browser is slower than real time, so a long file takes a while, with progress shown and cancel available.
Why do AVI files even need converting?
AVI is a 1992 container that predates streaming. It cannot represent modern codec features properly, its index design makes web playback awkward, and phone and browser support has quietly rotted away. The footage inside is often fine; it just needs a modern box, which is exactly what a remux gives it.
Is my file sent to a server?
No. Everything runs in your browser with ffmpeg compiled to WebAssembly. The file never leaves your device, which for a box of old family tapes is exactly how it should be.

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