AVI to MP4 Converter
Convert AVI to MP4 free — no upload, no signup
To convert AVI to MP4, drop your AVI video into the box below and click Convert. Fylo converts with ffmpeg running inside your browser, so nothing is uploaded and there's no signup or watermark. Old Xvid/DivX AVIs become modern H.264 MP4s, usually smaller.
Drop videos here
or tap to browse · paste with Ctrl+V · add many at once
Your files never leave your device
If the video already uses codecs that fit the new format, Fylo repackages it instantly with no quality loss.
Advanced
How to convert AVI to MP4
Add your AVI videos
Drag and drop AVI files into the box or tap to choose them. The converter engine (about 31 MB) downloads once, the first time you convert.
Choose quality (optional)
Balanced quality suits most videos. If the codecs already fit MP4, Fylo repackages the file instead of re-encoding it, with no quality loss.
Convert and download
Click Convert, then download each MP4 file or all of them as one ZIP.
Why convert AVI to MP4?
AVI files from old cameras, downloads and DVD rips won't play on iPhones, in browsers or on most social networks. MP4 makes them watchable everywhere.
What happens when you convert AVI to MP4?
AVI usually contains MPEG-4 Part 2 (Xvid/DivX) or MJPEG video, which Fylo re-encodes to H.264 with AAC audio. Because H.264 is more efficient, the MP4 is often 30–50% smaller at similar quality. If the AVI already holds H.264, the video is copied without re-encoding.
How does Fylo convert AVI to MP4?
Fylo reads the AVI with ffmpeg compiled to WebAssembly and writes H.264 (x264, constant quality CRF 23) with AAC audio, plus the faststart flag for instant web playback. AVI's usual codecs (MPEG-4 Part 2 (Xvid/DivX), MJPEG) can't go into MP4 as-is, so the video is re-encoded. Speed depends on your device: short phone clips take seconds, while on our slow test PC a 2-minute 1080p video took about 10 minutes. Only the first video and audio track are kept, and the original resolution is preserved unless you pick 1080p, 720p or 480p under Advanced.
What's the difference between AVI and MP4?
AVI (Audio Video Interleave) was introduced by Microsoft with Video for Windows in 1992. It's based on the RIFF container used by WAV and stores interleaved chunks of audio and video. In the 2000s, AVI files with DivX or Xvid (MPEG-4 Part 2) video and MP3 audio were the standard for downloaded movies.
MP4 (MPEG-4 Part 14) is a container format standardised in 2001 and based on Apple's QuickTime file structure. A container holds separately compressed video and audio streams plus metadata such as subtitles, chapters and cover art. Most MP4s use H.264 video and AAC audio; newer files may use H.265 (HEVC) or AV1.
Learn more: AVI format guide · MP4 format guide
| Property | AVI | MP4 |
|---|---|---|
| Developed by | Microsoft | MPEG (ISO/IEC 14496-14) |
| Introduced | 1992 | 2001 |
| Typical video codecs | MPEG-4 Part 2 (Xvid/DivX), MJPEG | H.264, H.265/HEVC, AV1 |
| Typical audio codecs | MP3, PCM, AC-3 | AAC, MP3 |
| Plays in web browsers | No | Yes — every browser |
| Compatibility | Windows, VLC, older DVD players and TVs | Universal: phones, TVs, editors, social media |
| Best for | Legacy players, old Windows software | Sharing, uploading, streaming, editing |
Frequently asked questions
Why does AVI to MP4 take time?
The video has to be re-encoded from the old codec. A typical laptop handles standard-definition footage faster than real time.
Will the MP4 play on my phone?
Yes — H.264 with AAC is supported by every modern phone.
Is my AVI file uploaded to a server?
No. Fylo runs ffmpeg, the same engine used by professional video tools, compiled to WebAssembly inside your browser. Your AVI file is read directly from your device and never sent anywhere.
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