Old codecs, real re-encode
AVI files from the 2000s usually hold DivX, Xvid, MJPEG or old MS-MPEG4 video — codecs the MP4 container was never meant to carry. Unlike MKV or MOV, there is rarely a shortcut here: the honest path is a full re-encode to H.264, and that is what this tool does. It takes real time, proportional to the video's length, and produces a file every phone, TV and editor of the last fifteen years will open.
Archives deserve better than a random server
These files are often irreplaceable — digitized tapes, birthday parties captured on a camcorder that was thrown away years ago. They convert on your machine, and the originals stay untouched on your disk. Keep them; an original is an original.
Frequently asked questions
Why is AVI slower to convert than MKV here?
MKV usually remuxes — a mere container swap. AVI's DivX-era codecs can't live inside MP4, so the video must be genuinely decoded and re-encoded, which takes time.
Is quality lost in the re-encode?
A little, as with any encode — the settings favor quality, and footage from 2000s camcorders is limited far more by the source than by this conversion.
My very old AVI fails — what now?
Some early codecs (Cinepak, Indeo) and broken indexes are stubborn. Try the Old Video Rescue tool on this site — it exists exactly for those.