Convert · runs on your device

Convert MP4 to AVI in your browser

Video Mender converts MP4 to AVI locally by re-encoding the video to MPEG-4 Part 2 with MP3 audio — the combination legacy AVI players actually expect.

Nothing is uploaded

Drop video files here

MP4 · M4V · MOV · MKV

Choose video files to convert

Output format

This page always writes AVI.

Video codec

DivX/Xvid-era video. Needed because AVI players of that generation expect it.

How to size the output

A constant quality target. File sizes vary with how demanding the footage is.

Quality — 8 of 10

Resolution limit

Files smaller than the limit are left alone. Capping usually looks better than lowering the bitrate.

Frame rate

Audio

Fast rewrapCopy streams without re-encoding when the codecs already fit

Lossless and near-instant when it applies. It cannot reduce file size, so turn it off if you need a smaller file.

Converting to AVI is going backwards on purpose, and there is usually a specific reason: an old editing suite, a DVD player that reads DivX from a USB stick, or industrial software that was certified years ago and never updated. Those systems do not just want the .avi extension, they want the codecs of that era.

So this page does the useful thing rather than the literal thing. It re-encodes your H.264 video to MPEG-4 Part 2 and your AAC audio to MP3, which is what a legacy AVI player expects to find. Simply renaming an MP4 to .avi produces a file those players reject, and putting H.264 inside AVI produces one they often reject too.

Be aware of the trade-off: MPEG-4 Part 2 needs roughly 60% more bits than H.264 for the same picture. The AVI will be noticeably larger than the MP4, or noticeably softer at the same size. That is the cost of compatibility with old equipment, not a defect in the conversion.

What this actually does to your file

Rewrap or re-encode

No rewrap path is offered. AVI predates modern per-frame timing and handles H.264 B-frames badly, so copying the stream across would produce a file that plays unreliably on exactly the old hardware this conversion exists to serve.

Quality

This is a lossy re-encode into a less efficient codec. To hold the same visible quality the AVI needs more bits than the MP4 did, so expect a larger file.

The AVI will usually be larger than the MP4 at comparable quality. MPEG-4 Part 2 is simply less efficient.
AVI has no reliable variable-frame-rate support. A fixed frame rate is written, which can very slightly alter timing on VFR sources such as screen recordings.
Do not convert to AVI for the web or for phones. Nothing modern plays it — this route is for legacy targets only.

How to use this page

Add the MP4 files you need in AVI form.
Leave the codecs at MPEG-4 video and MP3 audio unless your target device documents otherwise.
Consider capping resolution to 480p or 720p if the target is genuinely old hardware.
Start, then download the AVI files.

Where the result plays

Checked against the containers and codecs this page produces, stated conservatively.

Target	Works	Detail
Legacy Windows software	Yes	MPEG-4 in AVI is the format that generation of software was built around.
DivX-certified DVD players	Yes	These devices read MPEG-4 AVI from USB or disc; this is the main reason to convert.
Browsers and phones	No	No browser and no phone gallery plays AVI. Keep the MP4 for those.
Modern editors	Partly	They will import it, but there is no benefit over the MP4 you started with.

The formats involved

Format	Read	Write	What it is
MP4	Yes	Yes	The MPEG-4 Part 14 container. It is a wrapper, not a codec — an MP4 usually holds H.264 or HEVC video with AAC audio.
M4V	Yes	Yes	Apple's MP4 variant used by iTunes. Byte-for-byte it is an MP4; the extension exists so iTunes can flag optional FairPlay DRM.
MOV	Yes	Yes	Apple QuickTime. Structurally a close cousin of MP4, which is why MOV files can often be rewrapped to MP4 with no re-encode.
MKV	Yes	Yes	Matroska. The most permissive common container: it will carry almost any codec, plus multiple audio tracks, chapters and subtitles.
AVI	Yes	Yes	Microsoft Audio Video Interleave, from 1992. No native support for modern per-frame timing, B-frame handling is fragile, and the index sits at the end of the file.

Tested limits

Real ceilings measured on real devices, not a marketing claim of unlimited.

Limit	Desktop	iPhone / iPad	Why
File size — rewrap	1.3 GiB	384 MiB	Rewrapping never decodes a frame, so it tolerates far larger files.
File size — re-encode	1.0 GiB	256 MiB	Decoding holds uncompressed frames in memory, which is the real constraint.
Clip length — re-encode	4:00:00	30:00	Beyond this, progress reporting and memory behaviour stop being dependable.
Resolution — re-encode	4096 × 2160	1920 × 1080	A 4K frame is about 12 MB decoded, before the encoder allocates anything.

If something goes wrong

My DVD player still rejects the AVI.

DivX-certified hardware usually enforces limits on resolution and bitrate. Cap the resolution at 720p or 480p and choose Balanced rather than Near-original, then try again.

The AVI is enormous.

MPEG-4 Part 2 needs more bits than H.264 for equal quality. Lower the preset, or cap the resolution, to bring the size down.

Audio and video drift apart.

The source probably had a variable frame rate. Set an explicit frame rate such as 25 or 30 fps so AVI has the constant timing it assumes.

Your video never leaves this device

This is a structural property of the application, not a policy we ask you to take on trust. There is no upload endpoint, no API route and no server action anywhere in the codebase, so there is nowhere for a video to be sent even by mistake.

Conversion runs in WebAssembly inside this browser tab. The engine is served from this domain and loaded only when you start a job.
The Content-Security-Policy restricts network connections to this origin, so the page is not permitted to contact a third party at all.
Nothing is stored. Close the tab and every queued file and finished output is gone — which is also why you should download results before you leave.
There are no accounts and no AI. Anonymous page views are counted — which page, roughly what country, what kind of device — and nothing whatsoever about your files.

The repository contains a test that fails the build if any media byte is passed to fetch, XMLHttpRequest, sendBeacon or a WebSocket. See the privacy page for how that is verified.

Questions

Can I just rename an MP4 to .avi?

No. The extension does not change the internal structure, and a player expecting an AVI index and MPEG-4 streams will refuse the file. A real conversion has to rewrite both container and codecs.

Why does the AVI come out larger than the MP4?

Because MPEG-4 Part 2 is a much older codec and needs roughly 60% more bits than H.264 for the same picture. You are trading efficiency for compatibility with old equipment.

Why not put H.264 inside the AVI?

It is technically possible and practically unreliable. AVI has no proper mechanism for H.264 B-frame reordering, so the files stutter or desync on the legacy players that need AVI in the first place.

Is there any reason to prefer AVI today?

Only compatibility with specific old software or hardware. For any current use — web, phones, editors, TVs — MP4 is better in every respect.

Which audio codec should I choose?

MP3 is the safe default and what legacy AVI players expect. Uncompressed PCM also works and is even more compatible, at a considerable size cost.