AVI to MP4 Converter

AVI is an old Windows format with large file sizes. Convert to MP4 for a much smaller, universally compatible video file.

🔒 No upload ⚡ Instant ✓ Free ∞ No size limit

Why convert AVI to MP4?

AVI is one of the oldest container formats, developed by Microsoft in 1992 for early Windows multimedia. It still works on most desktop computers, but AVI files are typically 2–5 times larger than equivalent MP4s, and many modern devices, browsers, and platforms either reject them outright or play them inconsistently.

MP4 has become the universal video format. It's supported natively by virtually every device made in the last 15 years — phones, tablets, smart TVs, browsers, social media platforms — using modern codecs like H.264 that produce dramatically smaller files at the same visual quality.

If you have an AVI file you can't play on your phone, can't upload to Instagram or Twitter, or that's eating up storage, converting to MP4 solves all three problems at once.

About AVI

AVI (Audio Video Interleave) is a Microsoft container format from 1992. It's commonly seen in older recordings, screen captures, and some camcorder footage. AVI files can use various codecs internally, which is part of why playback compatibility varies so much across devices.

About MP4

MP4 (MPEG-4 Part 14) is the modern standard for video files. It uses efficient codecs like H.264 to compress video without noticeable quality loss, and it's supported by every major browser, phone, and operating system out of the box.

Quality and file size

Filesmith re-encodes the video using H.264 — a lossy codec, but the visible difference is minimal. Expect your MP4 to be roughly 50–70% smaller than the original AVI with no perceptible drop in quality on most footage. Audio is converted to AAC, the standard for MP4 containers.

AVI is the oldest container of the four and carries slightly more overhead, but the video inside is unchanged. Remuxing one 13.8-second 2160 × 1064 phone clip moved the size by about 35 KB out of 20 MB.

Same video stream · four containers 0.2% variance

Every one of those holds the identical video stream — the difference between them is a few hundred bytes of container overhead. That is why the conversion is near-instant even on a large file, and why the result is pixel-for-pixel identical to what you started with. Older AVI files sometimes carry codecs modern players reject — in that case the stream does have to be re-encoded, which takes longer and does cost quality.

How these figures were measured →

Filesmith runs entirely in your browser using WebAssembly. Files are never uploaded to any server — conversion happens locally on your device, instantly and privately.

Accepts: MP4, WEBM, MOV, MKV, AVI, FLV

Frequently asked

Will I lose quality converting AVI to MP4?

There's a small loss from re-encoding, but it's almost always invisible on standard playback. The file size savings (typically 50–70%) far outweigh the negligible quality drop on most footage.

Is there a file size limit?

No. Filesmith processes everything locally in your browser, so the only limit is your device's available memory. Multi-gigabyte files work fine on most modern computers.

Why doesn't my AVI play on iPhone or Android?

Most phones don't include the codecs needed to play AVI natively. MP4 is supported everywhere out of the box, which is the main reason people convert.