Convert AVI to MP4 Online — No Upload, No Watermark
AVI is an older Microsoft container still common in legacy recordings and DV camcorders. Converting to MP4 gives you a file that plays on every phone, browser, and editor without re-encoding at playback time.
Drag & drop your video here, or click to browse
Max file size: ~2 GB (memory permitting)
Where AVI files come from
AVI dates from Windows 3.1 and stayed the default for consumer camcorders, screen capture tools and DivX or Xvid downloads well into the 2000s. Files that turn up today are usually old camcorder tapes, archived home video, or clips from software that has not been updated in fifteen years.
What changes when you convert AVI to MP4
| Container | Rewritten to MP4 with the moov atom at the front, so it starts playing before it finishes downloading |
|---|---|
| Video | Re-encoded to H.264 at CRF 23, which is visually lossless for most footage |
| Audio | Re-encoded to AAC, the codec MP4 players expect |
Worth knowing first
AVI has no standard way to store variable frame rate or modern timecode, so some old files play at slightly the wrong speed or drift out of sync with their audio as they go. The conversion resamples audio to match the video clock, which fixes progressive drift. A fixed offset present from the first frame is a different problem and needs an editor.
FAQ
Why is my old AVI out of sync?
AVI stores audio and video in interleaved chunks with no reliable clock between them, so a file written by old capture hardware can drift further out as it plays. Re-encoding to MP4 locks audio to the video timebase, which removes progressive drift. A constant offset from the very start is not fixed by converting.
My AVI will not play at all. Will converting help?
Often yes. Many AVI files hold DivX, Xvid or an ancient MPEG-4 variant that modern players no longer ship a decoder for. FFmpeg still decodes all of them, so the converted H.264 file plays even when the original will not.
Will the file get bigger or smaller?
Almost always smaller, frequently by more than half. H.264 is far more efficient than the codecs of the AVI era, so the same picture needs much less data.
Is this AVI to MP4 converter really free and without upload?
Yes. The tool runs entirely in your browser using FFmpeg compiled to WebAssembly. Your AVI file never leaves your device — open the DevTools Network tab to verify zero uploads. No signup and no watermark. The practical size limit is the memory your browser gives this tab, which is generous on a computer and a few hundred megabytes on a phone.