AVI to MP4 Converter

Convert a legacy .avi into a modern MP4 that plays anywhere and takes less space. Done on your device — nothing is uploaded.

By LK Forge · Published 6 August 2026 ·

Drop your file here, or click to choose Processed privately in your browser — nothing is uploaded

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100% private. Your file is processed in your browser with ffmpeg (WebAssembly) and is never uploaded. Big or long files take longer and use more memory — for those, trim first.

What is the difference between AVI and MP4?

AVI (Audio Video Interleave) is Microsoft's RIFF-based container, introduced in 1992. It has no native support for variable frame rate or modern subtitle formats, and its common codecs — Cinepak, MJPEG, DivX and Xvid — need several times the bitrate of H.264 for the same picture, which is why a ten-minute AVI can run to several hundred megabytes. MJPEG is the worst case, because it stores every frame as a standalone JPEG with no interframe compression at all. Converting to MP4 re-encodes the video with libx264 at CRF 23 on the veryfast preset and the audio to AAC at 160 kbps, usually cutting the file substantially while making it playable on current phones, smart TVs and every browser. Odd pixel dimensions are padded to even values, as H.264 4:2:0 chroma sampling requires. The conversion runs locally through ffmpeg.wasm, so the AVI is never uploaded; the engine itself downloads once per session, on your first conversion.

How to Use the AVI to MP4 Converter

Three steps, all in your browser.

  1. Load your AVI

    Drag a .avi file onto the box or click to choose one. AVI is an older Windows video format.

  2. Convert to MP4

    Click Convert. The tool re-encodes the video to H.264 and the audio to AAC in an MP4 container.

  3. Download the MP4

    Preview and download the .mp4 — smaller, modern and playable on current phones, players and the web.

Will a DivX, Xvid or Cinepak AVI from 2005 still open?

AVI is a 1992 Microsoft container — the awkward part is always the codec someone picked at the time.

AVI stores only a four-character code (a FourCC) naming the codec used. If the matching decoder is missing, you get audio and a black screen — the file itself is fine.

FourCCCodecEraDecodes hereWhat to expect
DIVX / DX50DivX 4–5 (MPEG-4 Part 2)2001–2006YesRe-encoding usually shrinks the file
XVIDXvid (MPEG-4 Part 2)2002–2010YesSame family as DivX
DIV3 / MP43MS MPEG-4 v31999–2002YesPre-standard Microsoft codec
MJPGMotion JPEGWebcams, camerasYesEvery frame a keyframe; large but robust
dvsdDV (DV25)Camcorder captureYesInterlaced, non-square pixels
cvidCinepak1992–1998YesVery low quality ceiling; no improvement possible
IV50 / IV41Indeo Video 4–51995–2000Build-dependentThe browser ffmpeg build carries a reduced decoder set
HFYU / rawHuffYUV or uncompressedCapture mastersYesEnormous input; expect a long conversion

Two artefacts this tool does not fix. Interlacing: AVI captured from DV camcorders, TV tuner cards or DVD rips is usually interlaced 480i or 576i. There is no deinterlace step here, so horizontal comb teeth on moving edges get encoded permanently into the H.264 output. If you see combing in the preview, deinterlace on a desktop tool first. Non-square pixels: DV and DVD-sourced AVI is 720×480 or 720×576 with an aspect flag rather than square pixels, so players that ignore the flag show a slightly stretched picture.

The upside is real. MPEG-4 Part 2 — what DivX and Xvid actually are — needs appreciably more bitrate than H.264 for the same perceived quality, and the 1990s codecs are far worse again. Re-encoding a genuinely old AVI at CRF 23 usually yields a much smaller file that looks no worse. If your file is a modern container instead, MKV to MP4 covers the opposite case — a current wrapper that players still reject.

Frequently Asked Questions

How do I convert AVI to MP4?
Load your .avi file and click Convert. The tool re-encodes it to an MP4 with H.264 video and AAC audio in your browser, then lets you preview and download it. No install and nothing uploaded.
Why convert AVI to MP4?
AVI is an old container that often uses dated codecs, producing large files that modern phones, browsers and editors may not play. MP4 with H.264 is smaller and far more compatible, so old clips become easy to watch, share and edit. This converter re-encodes to H.264 at CRF 23 with AAC audio at 160 kbps.
Is my video uploaded anywhere?
No — your AVI never leaves your device. Everything runs locally with ffmpeg compiled to WebAssembly. Your file is never uploaded, logged or stored, so it’s safe for personal footage. The video engine (about 10 MB) downloads the first time you convert in a session; after that, no further network requests are made.
Will the file get smaller?
Usually the MP4 is smaller. Older AVI files are frequently encoded inefficiently, so re-encoding to H.264 at CRF 23 commonly produces a noticeably smaller MP4 at similar visual quality. How much smaller depends on the codec and bitrate the AVI already used, so it is not guaranteed.
Is there a size limit?
The size limit comes from your browser, not from us: the video engine is 32-bit WebAssembly and holds the input and the output in memory at once, so files much over about 1 GB can run out of memory. Because the work happens in your browser, very large or long files use more memory and take longer to convert. Shorter clips finish quickly.

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