What is this AVI to MP4 converter?
A free, browser-based tool that converts a AVI video to MP4. Add a file, preview it inline, and download the result. All processing happens locally in your browser, so your video is never uploaded and there is no watermark.
When an old AVI refuses to play: MP4 as the fix
The problem usually surfaces at the worst moment: a clip from a digitized family tape will not AirDrop to a phone, PowerPoint shows a black box instead of the 2008 product demo, the web player rejects the upload. Modern devices standardized on MP4 with H.264 years ago, and AVI quietly fell off the support lists.
Converting to MP4 turns that stranded footage back into working material: something you can drop into a slide deck, post as a social clip, or send to relatives without playback instructions.
H.264 inside the AVI remuxes; DivX and Xvid re-encode
What happens next depends on the codec hiding inside the container. Some later AVIs already carry H.264, and MP4 accepts H.264 directly, so those files remux: the streams are copied over unchanged, done in an instant, quality untouched.
The classic 700MB DivX or Xvid file is another story. MP4 holds H.264, H.265, and AV1, not those 2000s codecs, so the video is re-encoded. That adds one lossy generation, which is why the original AVI should stay on disk as the master while the MP4 does the traveling. If you are unsure what your file holds, just convert it: a run that finishes instantly was a remux.
How to use it
- Add a AVI file on the left (drag & drop or click) — it shows an inline preview.
- Pick a quality preset (used only when the video has to be re-encoded).
- Press “Convert & download” to get your MP4 file. The first run downloads the ~30MB converter once.
Lossless remux vs re-encoding
AVI and MP4 are containers — what matters is the video codec inside. When the codec already fits MP4, this tool just repackages it (a "remux"): instant and completely lossless. Only when the codec isn't compatible — most often anything involving WebM — does it re-encode the video locally, which takes longer and is where the quality preset applies.