Convert AVI to MP4 Online
xFormat converts legacy AVI files to modern MP4 (H.264/AAC) in your browser, using a compatibility engine because browsers cannot decode most AVI natively, and nothing is uploaded.
Runs in your browser — files never leave your device.
How it works
AVI is a veteran format from the Windows 95 era. Phones, smart TVs and many websites no longer play it well. This tool rescues old camcorder clips, downloaded movies and family videos by converting them to MP4. It can be slower than other conversions, so a little patience helps.
- 1
Select your AVI file.
- 2
Choose MP4 as the output format.
- 3
Click Convert, wait for the engine to load and finish, then save.
Why AVI is a special case
Browsers have built-in decoders for modern formats such as H.264, but AVI files often hold older codecs such as DivX, Xvid or Motion JPEG that browsers cannot decode directly. For these, the converter switches to a compatibility engine that can read older codecs.
The first time you use it, your browser downloads a roughly 31 MB engine, and later visits reuse the cached copy. After that, the video is processed locally with no upload.
What to expect
Almost every AVI needs a full re-encode to H.264 video and AAC audio, because old codecs cannot be copied into a modern MP4. The compatibility engine is not as fast as a native desktop app or hardware encoding, so long or large AVIs may take noticeably longer. Keep the tab open and avoid switching your phone to the background while it runs.
The upside is a much smaller, more compatible file. Old AVIs are often large for their quality, and a modern codec can usually shrink them considerably.
Size limit
Try to stay below about 500 MB on desktop and 200 MB on a phone.
Frequently asked questions
Why is AVI to MP4 slow?
AVI usually has to be fully re-encoded, and it runs on the compatibility engine, which is slower than hardware-accelerated conversion. Large files take proportionally longer.
What is the 31 MB download?
It is the compatibility engine that reads older formats such as AVI. It downloads once, is cached by your browser, and is used only to process files on your own device.
Will the MP4 be smaller than my AVI?
Often yes, since modern codecs are more efficient, but the result depends on the original codec and settings.
Is my AVI uploaded to a server?
No. Only the engine is downloaded; your video stays on your device.
Does it work on phones?
Yes, but conversion is slower and memory is limited, so keep files under roughly 200 MB.
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