Convert AVI to MP4
Modernise old AVI clips into MP4 that plays on any phone or browser. DivX and Xvid are re-encoded to H.264 on your own machine — no upload.
- Runs in your browser
- Files are never uploaded
- Free, no account
First use downloads the 10 MB video engine from this site. After that it is cached and works offline. It is WebAssembly served from onthisdevice.com — no third-party CDN — and your file is still processed entirely on your own device.
Bringing a 2003 file into 2026
AVI is a Microsoft container from 1992. It predates almost everything modern video assumes: it has no reliable way to store variable frame rates, no standard place for aspect-ratio metadata, and no concept of the B-frames that modern codecs depend on. What it does have is a very long tail of home videos, camcorder captures and DivX-era downloads that people still need to open — on a phone that has never heard of it.
Converting to MP4 is nearly always a genuine re-encode rather than a re-wrap, because the video inside is usually MPEG-4 Part 2 (DivX, Xvid) or an even older MJPEG or Cinepak stream. Modern devices decode H.264 and not much else, so the frames really do have to be rebuilt. This page inspects the file first and tells you which of the two paths it is taking.
Common AVI problems and what fixes them
| Symptom | Cause | Result after converting |
|---|---|---|
| Phone or TV refuses the file entirely | The AVI container itself | Fixed — MP4 is universally supported |
| Video plays, no sound | AC-3, ADPCM or a proprietary ACM audio codec | Fixed — audio is re-encoded to AAC |
| Green or blocky picture in a browser | Xvid packed bitstream | Fixed by the re-encode |
| Everyone looks stretched or squashed | Non-square pixels with no aspect metadata | Usually fixed; check the preview before saving |
| Combing lines on fast motion | Interlaced footage from a camcorder or TV capture | Not fixed — deinterlacing is not applied here |
| Audio drifts out of sync over time | VBR MP3 audio in a container that assumed CBR | Usually fixed, because the audio is rebuilt with proper timestamps |
What to expect from the quality
Re-encoding always loses something, and there is no honest way around that: the AVI has already been compressed once, and compressing the decoded result a second time discards more. What you can control is how much. The high quality preset (CRF 18) keeps essentially everything an old standard-definition source has to offer and produces a file a little larger than the original. Balanced (CRF 23) is the sensible default. Small file (CRF 28) is for when you are emailing a clip and the content matters more than the grain.
Old footage is low resolution — typically 640×480 or 720×576 — so encoding is fast, roughly real time or better on any modern laptop, and the resulting MP4 is usually much smaller than the AVI it came from. H.264 is simply a far better codec than anything that shipped in 2003.
Archiving a shelf of old files
If you are working through a folder of family videos, convert at the high-quality setting and keep the originals. Storage is cheap; a re-encode cannot be undone. Convert once, to a format you can still open in twenty years — H.264 in MP4 is currently the safest bet available, and it is the one format every phone, browser, TV and editor agrees on.
Everything happens on your own machine, which matters more than usual with home video: there is no upload step, no retention window on someone else’s server, and no account attached to the footage of your family.
Questions
Will my AVI file convert instantly like MOV files do?
Usually not. AVI files from the DivX and Xvid era hold MPEG-4 Part 2 video and MP3 audio. MP4 can technically carry both, so a copy is sometimes possible, but many old AVI files also carry quirks — packed bitstreams, VBR MP3 with a broken header — that only survive a proper re-encode. The page inspects your file and tells you which path it will take.
Why does my AVI have no sound on a phone?
AVI often carries AC-3 or an old ADPCM variant that mobile devices never decode. Converting here re-encodes the soundtrack to AAC, which every phone plays, so the sound comes back.
The video looks interlaced — can that be fixed?
Not automatically here; deinterlacing is a separate filter and applying it blindly softens progressive footage. If you see combing on fast motion, that is interlacing from an old camcorder or TV capture, and it is a genuine limitation of this tool rather than something we hide.
How long does a re-encode take?
Roughly real time on a modern laptop for standard-definition AVI — a 10-minute clip in around 10 minutes. Progress is shown as a real percentage of the clip, not a spinner, and you can cancel at any point.