Compress · runs on your device

Compress AVI files in your browser

AVI files compress unusually well because the video inside is old and inefficient — re-encoding an Xvid or DivX AVI to H.264 typically halves the size with no visible quality loss.

Nothing is uploaded

Drop video files here

AVI

Choose video files to convert

Output format

Plays on effectively every browser, phone, TV and editor when it holds H.264 and AAC.

How to size the output

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

Quality — 6 of 10

Resolution limit

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

Frame rate

Audio

Platform presets — editable

These are dated observations, not permanent platform limits — all were last checked on 2026-08-01. Every one sets an ordinary target size you can edit afterwards.

AVI is where compression gives you something close to a free lunch, and it is worth understanding why. The video inside a typical AVI is MPEG-4 Part 2 — Xvid or DivX — which needs roughly 60% more bits than H.264 to produce the same picture. Re-encode to H.264 at matched quality and the file halves. That is efficiency you are gaining, not detail you are losing.

The container is inefficient too. AVI carries per-chunk overhead that adds up across a long file, and it has no proper support for modern variable frame timing. Moving to MP4 removes that overhead as a side effect.

Which is why output defaults to MP4 rather than AVI, and this page says so instead of doing it quietly. If you genuinely need the AVI container — old hardware, certified legacy software — switch the output to AVI and the file is re-encoded as MPEG-4 inside AVI. It will be larger than the MP4 for the same quality, which is the price of that compatibility.

What this actually does to your file

Rewrap or re-encode

Copying the streams into a new container would strip the AVI overhead but leave the inefficient Xvid video intact, so it barely reduces the size. Real compression here means re-encoding the video, which is why fast rewrap is off.

Quality

This is a lossy re-encode of an already lossy source, so generation loss applies. The efficiency gain from H.264 usually more than covers it: matched quality at roughly half the size is the normal outcome.

Old AVI footage is often interlaced. This tool does not deinterlace, so combing in the source remains in the output.
A truncated AVI — the index sits at the end of the file — may play in VLC but fail here. That is reported as a failure rather than written as a broken output.
Choosing AVI output means MPEG-4 video, which is less efficient. Expect a bigger file than the MP4 at equal quality.
Motion JPEG AVI files are effectively uncompressed video. These shrink enormously and are the best case on this page.

How to compress AVI files

Add your AVI files — an entire folder of an old collection is the normal case.
Leave the output as MP4 unless a specific old device requires AVI.
Choose Balanced quality, or set a target size in megabytes.
Start the queue; standard-definition AVI encodes quickly.
Download each result, or select several and take a ZIP with a manifest.

Where the result plays

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

Target	Works	Detail
MP4 output (default)	Yes	H.264 and AAC. Smaller, and plays on everything AVI does not.
AVI output	Partly	MPEG-4 and MP3 inside AVI, for legacy hardware and software only.
Browsers and phones	No	Nothing modern plays AVI in any form. Choose MP4 output.
DivX-certified players	Partly	Keep AVI output and cap the resolution; these devices enforce their own limits.

The formats involved

Format	Read	Write	What it is
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.
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.
MKV	Yes	Yes	Matroska. The most permissive common container: it will carry almost any codec, plus multiple audio tracks, chapters and subtitles.

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

Why is the output an MP4 rather than an AVI?

Because H.264 in MP4 gives a substantially smaller file at the same quality, and plays on devices AVI never will. Switch the output container to AVI if you need it; nothing is renamed without your choosing it.

The AVI failed part way through.

It is probably truncated. AVI stores its index at the end of the file, so an incomplete copy breaks processing even though a forgiving player may show part of it.

Audio and video drift apart in the output.

The source likely declared a frame rate it does not keep. Set an explicit frame rate — 25 or 30 fps depending on origin — and run it again.

The compressed file is barely smaller.

Check what the source actually contains. An AVI that already holds H.264 has no efficiency gain available, so only a genuine bitrate reduction will shrink it.

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

How do I compress AVI files?

Re-encode the video to H.264 and, unless legacy hardware forces otherwise, write it into MP4. Add the files here, pick a quality preset or a target size, and it runs in your browser without uploading anything.

How much smaller will my AVI get?

Around half the size at matched quality is typical for Xvid or DivX sources, because H.264 is that much more efficient. Motion JPEG AVI files shrink far more; an AVI already holding H.264 shrinks much less.

Can I compress an AVI and keep it as an AVI?

Yes — set the output container to AVI and it is re-encoded as MPEG-4 with MP3 audio. The result is larger than the MP4 equivalent at the same quality, which is the cost of legacy compatibility.

Will compressing make old footage look worse?

Slightly, since it is another lossy generation. At the Balanced preset on standard-definition footage the difference is very hard to see, and the efficiency gain more than pays for it.

Can I compress a whole folder of AVI files at once?

Yes, and that is the common case for digitised collections. Queue the folder, apply one preset to everything, and download results as they finish so nothing large is held in memory.