AVI is a 90s-era Microsoft container that's been outclassed by MP4. Converting cuts file size, improves quality at the same size, and replaces a format that's increasingly poorly supported on modern devices.
Convert AVI to MP4 – Free Online AVI to MP4 Converter
Why convert AVI to MP4?
- Watch old AVI files on smart TVs, streaming sticks, and mobile devices.
- Stream via HTML5 video and modern web platforms.
- Reduce file size — modern H.264/H.265 in MP4 is dramatically more efficient.
What is the difference between AVI and MP4?
| AVI | MP4 | |
|---|---|---|
| Container origin | Microsoft, 1992 — the Video for Windows era | ISO standard from 2001, still current |
| Typical codecs inside | DivX, Xvid, or MJPEG video with MP3/AC-3 audio | H.264/H.265 video with AAC audio |
| Compression efficiency | Needs 2-3x the bitrate for a comparable picture | Modern codecs pack the same quality into far fewer bits |
| Streaming/web use | None — predates web video; no seeking-friendly structure | Built for progressive download and HTML5 playback |
| Best for | Nothing new — only feeding legacy software that requires it | Everything: playback, sharing, uploading, archiving |
Does converting AVI to MP4 lose quality?
This is a re-encode by nature, not a rewrap: the DivX/Xvid-era codecs inside typical AVIs are not what MP4 players expect, so every frame is decoded and compressed again into a modern codec. That single generation of loss is minor next to what the source already lost in its original 2000s encode — grain, blockiness, and softness in the AVI are faithfully preserved, not created, by the conversion.
Resolution and frame rate pass through untouched, which for this pairing usually means standard definition at 25 or 29.97 fps. Some AVI-era footage is interlaced (from TV captures and camcorders); combing artifacts on fast motion in the output trace back to that, not to the conversion itself. Mono or stereo MP3/AC-3 audio comes out as AAC with no audible change.
AVI's biggest playback sin — audio drifting out of sync over long files, caused by variable-bitrate MP3 tracks the old container never handled well — is often cured by conversion, because the MP4 is muxed with fresh, accurate timestamps.
What can go wrong converting AVI to MP4?
- The audio drifts out of sync partway through the video — If the drift exists in the converted MP4, it was almost certainly present in the AVI itself (a classic VBR-MP3 problem). Check the source in VLC first; a desktop remux tool can rebuild timestamps on stubborn files.
- The conversion fails or stops partway — Half-downloaded AVIs from the file-sharing era often have truncated data or a broken index. Verify the whole file plays locally from start to end before uploading it.
- My AVI is bigger than the 50 MB free limit — Old AVIs are bloated by inefficient codecs, so even short clips can pass 50 MB. Split long files into shorter segments before converting, or process a full-length file with a desktop converter.
How to convert AVI to MP4
- Upload your AVI file using the area above.
- MP4 is preselected as the target format.
- Click Start and wait for the conversion to finish.
- Download your converted MP4 file.