AVI to MP4 Converter
Convert old AVI videos to modern H.264 MP4 in your browser, with a quality choice. Free, private, no signup or upload.
About the AVI to MP4 Converter
This free AVI to MP4 converter modernizes old AVI clips into H.264 MP4 — the format supported by phones, browsers, editors and social platforms. AVI is an older container that many devices no longer play smoothly; converting to MP4 makes your footage universally compatible and usually smaller.
The conversion runs in your browser through FFmpeg WebAssembly, so your video is never uploaded. The engine (about 30 MB) downloads from a CDN on first use and is cached, so the first conversion is the slow one. The output uses a web-friendly yuv420p pixel format and even dimensions, which H.264 requires, so it plays correctly everywhere.
Converting re-encodes the video, so it takes a little time and cannot add quality beyond the AVI source — but a higher quality setting keeps more detail. Files up to 100 MB are supported.
How to Use the AVI to MP4 Converter
- 1Choose an AVI file, up to 100 MB.
- 2Pick a quality — Balanced is recommended.
- 3Click Convert to MP4 and wait for the progress bar.
- 4Preview the MP4 and download it.
Frequently Asked Questions
Is my file uploaded to a server?
No. All processing runs in your browser using FFmpeg compiled to WebAssembly. Your file never leaves your device — only the converter engine is downloaded, once.
Why is the first run slow?
The first time you use any converter here, the browser downloads the FFmpeg core (about 30 MB) from a CDN and compiles it. It is then cached for the session, so later runs are much faster.
Why convert AVI to MP4?
AVI is an older format many phones, browsers and apps struggle to play. MP4 with H.264 is supported almost everywhere and is usually smaller for the same quality.
Will the MP4 look worse than the AVI?
At the High or Balanced setting the difference is very hard to see. Converting cannot add quality beyond the source, but a good quality setting preserves almost all of it.
Is there a file size limit?
Yes, 100 MB per file. Because everything runs in your browser's memory, very large files can be slow or run out of memory. Trim long clips first if you hit the limit.