Convert AVI to MP4 Online Free in Browser
Convert AVI to MP4 online for free. The old DivX or XviD inside an AVI compresses far worse than H.264 — the file gets lighter.
AVI dates from 1992 and carries old codecs — DivX, Xvid, sometimes no compression at all. MP4 with H.264 holds the same picture in a fraction of the space and decodes in hardware even on a cheap phone. So old recordings do not merely start opening on modern devices after conversion — they also get noticeably lighter.
Drop files here
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Video · audio · images — several at once is fine
Files
Input file is available as input. Specify the output filename at the end of the line (e.g. output.mp4).
Frequently asked questions
Why is my old AVI so heavy?
An AVI usually carries an old codec — DivX, XviD, sometimes plain MJPEG — which compresses several times worse than modern H.264. Converted to MP4, the same movie normally takes noticeably less space.
Will the subtitles survive?
External .srt subtitles do not travel inside the file. Keep them next to the MP4 under the same name and the player will pick them up.
What if the AVI will not play at all?
It most likely holds a rare codec your system lacks. Conversion solves exactly that: the file is taken apart and rebuilt as H.264, which every player understands without extra installs.
Where do my files get uploaded?
Nowhere. All processing happens locally in your browser using FFmpeg.wasm — files never leave your computer.
Is it free to use?
Yes, this tool is free and needs no sign-up. Your file is processed right in your browser and is not uploaded to a server. There are no watermarks.