Free tool · Convert
AVI to MP4
Convert AVI files to the modern MP4 format.
Convert an older AVI file into MP4, re-encoded with H.264 video and AAC audio for playback on virtually any modern device or website. AVI files often use dated codecs, so this conversion typically improves both compatibility and file size.
- Files never leave your device
- Runs entirely in your browser
- Free, no account needed
How to use AVI to MP4
Two steps, and nothing to install.
Drop your AVI file
Add the video. Older files are often large, and everything is read locally.
Download the MP4
Save the modern H.264 and AAC result, usually noticeably smaller than the original.
More free tools
Free, private, and no sign-up on any of them.
How this works in your browser
This is a full re-encode rather than a container swap, because the codecs inside a typical AVI are not ones MP4 carries. Each frame is decoded from the original codec, then encoded again with H.264, while the audio is re-encoded to AAC. The encoder runs at its fastest preset, a necessary compromise given that the WebAssembly build is single-threaded with no GPU access. The index is written at the front of the output so playback can begin before the file finishes downloading. The size reduction comes from the generational gap in compression efficiency: H.264 describes the same picture with far fewer bits than the codecs AVI files typically carry.
AVI to MP4 vs. upload-based online tools
| Feature | AVI to MP4 (in-browser) | Upload-based online tools |
|---|---|---|
| File upload required | No - never leaves your device | Yes - file is sent to a server |
| Processing queue | None - starts instantly | Often, especially at peak times |
| Watermark on output | Never | Common on free plans |
| Usage limits | None - free, unlimited use | Often capped per day or file size |
| Works offline once loaded | Yes, for most tools | No - requires a live connection |
| Account required | No | Often, for anything beyond a trial |
Who uses AVI to MP4
Reviving an old video library
Convert archived AVI recordings into a format current devices and software still play.
Uploading legacy footage
Get an old file past platforms and forms that will not accept AVI.
Reclaiming disk space
Shrink a collection of inefficiently encoded videos you want to keep.
Editing older material
Bring dated footage into modern editing software in a format it handles smoothly.
Frequently asked questions
What it can and cannot do, and what happens to your files.
Will the MP4 be smaller than the AVI?
Usually yes. AVI files often use older, less efficient codecs, so re-encoding to H.264 typically shrinks the file.
Does this work with any AVI file?
It works with standard AVI files. Very old or unusual codecs inside the AVI container may not decode correctly.
Is audio preserved?
Yes, the audio track is re-encoded to AAC alongside the video.
Why is my old AVI file so large?
Because AVI dates from an era before modern compression. Many AVI files use codecs that predate H.264 by a decade or more, and some hold barely compressed video at all. Re-encoding to H.264 frequently cuts the size substantially while looking the same, which is a rare case of getting both.
Will converting make an old video look better?
No, and it is worth setting expectations. Whatever detail the original encoding discarded is gone permanently. What you gain is a file that plays everywhere and takes far less space, not a restored picture.
My AVI will not convert. What now?
AVI was a general-purpose container that held a wide variety of codecs over the years, some of them proprietary and long abandoned. If the video inside cannot be decoded, no conversion is possible. Playing it in VLC, which bundles an unusually broad set of decoders, and exporting from there is the usual way through.
Is my video uploaded anywhere?
No. The decode and re-encode both run inside your browser tab.
Convert AVI to MP4 - free, modern compatibility.
Files never leave your device. No upload, no account, and free for unlimited use.
Also see: MP4 to AVI