Free AVI to MP4 Converter No upload, and honest about the wait
AVI came out of Microsoft in 1992 and it has not moved since. The video inside is usually MPEG-4 Part 2, the codec sold as DivX or XviD, and and support for it on phones and in browsers is poor whichever container it sits in. So this page always re-encodes to H.264 instead of repackaging, which means it runs at roughly the speed of the footage itself. A ten minute AVI takes about ten minutes. What comes back is a file phones open, browsers play and editors import, and all of it happens in this tab, so the video is never sent to us.
- H.264 MP4 out
- Runs in this tab
- 20 files per batch
Convert AVI to MP4
MP4, MOV, M4V, MKV, AVI, WMV, WebM, TS, MTS and more
Up to 20 clips at once
Privacy-first. No uploads. If this helps, share it.
- The oldest files you own stay on your machine
An AVI is usually something captured off a camcorder tape, dug out of an old hard drive or exported by software nobody runs anymore. There tends to be exactly one copy. FFmpeg compiled to WebAssembly does the work inside this page, so no version of it is handed to a server and nothing is kept on our side.
- It re-encodes, so it takes real time
AVI is one of the formats with no shortcut. Every frame is decoded and written again as H.264, the browser build runs on a single thread, and the job takes roughly as long as the video runs. Worth knowing before you queue an hour of holiday footage.
- A whole folder of old clips in one go
Add up to 20 AVI files at 1 GB each. They convert one after another rather than side by side, so plan around the total runtime of the batch instead of the longest file in it.
How to convert AVI to MP4
Add the AVI, wait for the encode to finish and download the MP4. There is no fast path for this format. AVI goes straight to a full H.264 and AAC re-encode rather than being repackaged, so every frame is decoded and written again. That runs at roughly real time on a single browser thread, which makes a two minute clip quick and a forty minute recording a coffee break. The picture drops very slightly along the way, and that is the price of a file that opens on a phone.
- Add your AVI files
- Let the re-encode run
- Download the MP4
What is actually different between AVI and MP4
Both are containers, boxes that hold a video stream and an audio stream. The difference is the age of what sits inside them, and what current hardware is willing to do with it. This is the table that explains why an AVI plays fine on one Windows desktop and almost nowhere else.
| What changes | AVI | MP4 |
|---|---|---|
| Container | Audio Video Interleave, published by Microsoft in 1992 as part of Video for Windows. | The ISO base media container that phones, browsers, editors and TVs expect by default. |
| Video codec | Usually MPEG-4 Part 2, badged DivX or XviD. Older files can hold MJPEG, or 1990s codecs like Cinepak and Indeo. | H.264, encoded fresh every time. AVI never takes the repackaging shortcut that MOV and MKV often get. |
| Audio codec | Commonly MP3, sometimes AC-3, occasionally raw PCM straight off a capture card. | AAC, which every MP4 player handles without a codec pack. |
| Where it plays | VLC, and Windows desktops with the right codecs installed. Very little else. | iPhone, Android, Safari, Chrome, upload forms, editors and smart TVs. |
| File size | Often large for how it looks, because the codec is two generations behind. | Usually smaller for the same visible quality, because H.264 is more efficient. Not a promise, and the picture is still the one you started with. |
Drop something that is not an AVI into the box and it converts anyway. The file is relabelled to whatever actually arrived, so a stray MOV or MKV sitting in a folder of old clips does not stop the batch.
You lose a little, and you gain a file that works
Converting AVI to MP4 is not free. MPEG-4 Part 2 has to be decoded and written again as H.264, and every re-encode gives something up, so the MP4 comes back very slightly softer than the AVI was. It is worth being blunt about the starting point too. Most AVI files are old, were encoded at a low bitrate for a hard drive that cost real money, and already look their age. Converting will not sharpen them, undo the blocking or bring back detail that was thrown away in 2006. What it does is turn a file only one computer in the house will open into one that plays on a phone, uploads to a form, imports into an editor and streams in a browser.
Sources like MOV and MKV often skip the re-encode, because the streams already inside them can be repackaged into MP4 untouched. AVI is not given that attempt: even where the old video could be repackaged, phones, Safari and QuickTime still refuse to play the result, so it goes straight to H.264. That is why this is one of the slower pages, and why the tab has to stay open until it finishes.
Where the MP4 plays, and what converting will not fix
An H.264 MP4 with AAC audio is about as close to universal as a video file gets. Phones, tablets, browsers, upload forms, messaging apps, editors and smart TVs all take it, and most of them decode H.264 in dedicated hardware, which is something AVI's codecs never get. That is why a clip that made a laptop fan spin as an AVI plays quietly on a phone as an MP4. The conversion has limits though, and they are worth knowing before you queue a folder of them.
Editors take it. Premiere, Resolve, Final Cut, iMovie and CapCut all import H.264 MP4, where an old DivX AVI is the file that lands with no picture, no sound or a timeline that will not scrub.
It will not look better than the AVI did. Compatibility is the win here, not quality, and interlaced camcorder footage stays interlaced, because this tool does not deinterlace.
A subtitle file sitting next to the AVI stays a separate file. This page changes format and can pull the audio out as an MP3. It does not merge in an SRT, trim length, crop the frame or change the aspect ratio.
Convert an AVI in three steps
None of them involve a server.
Add your AVI files
Drag them onto the box, or pick them from your drive the usual way. The batch holds 20 files and each one can be 1 GB, which covers most screen recordings and short camcorder exports. Raw DV captured off a tape can run past that on its own, and anything over the limit is turned away.
Leave the output on MP4
The To dropdown is already set to MP4, which gives you H.264 video with AAC audio. Switch it to MP3 if the sound is all you were after, which returns 128 kbps audio at 44.1 kHz and skips the picture entirely, so it also finishes a good deal quicker.
Wait it out, then download
Progress moves at roughly the speed of the footage. Keep the tab in the foreground, especially on a phone, because a suspended tab stops the encode partway through. Save each MP4 as it lands, or collect the finished batch as a zip.
Why AVI stopped working everywhere
Nothing broke. The rest of the world moved to a format that phones and browsers could decode in hardware, and AVI was never rebuilt to follow it.
Phones and browsers never took it
There is no AVI support to fall back on in iOS, Android or Safari. The file arrives, the player looks at it and offers a download instead of playback, which is how most people find out their old clips have become a problem.
Upload forms reject it on the extension
Application portals, learning platforms, claim forms and council websites publish a short list of accepted file types, and AVI is rarely on it. The check runs before anything looks inside the file, so how good the video is makes no difference to the answer.
No hardware decoding, so it costs battery
H.264 is decoded by a dedicated block in almost every phone and laptop chip made this decade. MPEG-4 Part 2 is not, so playback falls back to software, which runs slower, hotter and heavier on battery when the file plays at all.
One conversion beats installing a codec pack
The old fix was a codec pack, and those were a well known way to break a Windows install. Converting once gives you a file that needs nothing installed anywhere, on any machine you send it to.
An old AVI is usually the only copy left
The files that turn up on this page are rarely disposable. They are wedding tapes someone captured to a hard drive, a parent's camcorder footage, a business recording from an office that no longer exists, a screen capture of software nobody can run. Handing the only copy to an upload based converter, where it waits in a queue on a machine you know nothing about, is a lot to risk for a change of container.
There is no upload step here at all. The page reads the file off your disk, FFmpeg compiled to WebAssembly re-encodes it in memory, and the result comes back as a download. We never see the video, its name or its length, and there is no account for any of it to hang off. Nothing has to be deleted from our side afterwards, because nothing was ever there.
What that actually means
- The file is opened by your browser, not by us
- No copy is queued, stored or cleaned up later on our side
- No account, no watermark, no daily quota on how many you convert
- Your own processor does the encoding, so long files take real time
AVI conversion troubleshooting
Related conversions
Need a different format? These open the same private browser converter, preconfigured for another conversion.
- WMV to MP4
Turn old Windows Media files into MP4 that modern devices will actually open.
Open this converter - M4V to MP4
Turn Apple's M4V into a standard MP4. Seconds, no quality loss, no upload.
Open this converter - MTS to MP4
Turn AVCHD camcorder clips into MP4 that phones and browsers will actually open.
Open this converter
More free tools
Convert Video
Convert almost any video to MP4 or MP3 in your browser. Nothing is uploaded.
Open toolCompress Video
Shrink a video to fit Discord, WhatsApp or email size limits. Private, in your browser.
Open toolRemove Audio from Video
Strip every audio track from a video. Free, in your browser, no upload.
Open toolFrequently asked questions
Add the file on this page, wait for the encode to finish and download the MP4. It runs in your browser, so there is no upload, no account and no watermark on the file that comes out.
AVI and MP4 playback notes last reviewed on 15 August 2026.