AVI to MP4 Converter. Make Old AVI Files Play Everywhere, Free
Turn a legacy AVI that won't open on your phone, browser or upload form into a clean, universal H.264 MP4. Real FFmpeg transcoding with web-ready faststart, an in-page preview, and a download, all on your device, never uploaded, no watermark, no sign-up.
What is the avi to mp4?
The AVI to MP4 converter re-encodes legacy AVI files (DivX, Xvid or MJPEG video with MP3 or PCM audio) into universal H.264/AAC MP4 using FFmpeg in your browser. A genuine transcode with yuv420p pixels and web-ready faststart, plus an in-page preview and download. Free, and nothing is uploaded.
This AVI-to-MP4 converter runs a full FFmpeg build compiled to WebAssembly directly in your browser and re-encodes your clip's video to H.264 and its audio to AAC inside an MP4 container: the format that virtually everything on earth can play. AVI is a legacy Microsoft container from the 1990s: the files inside it are usually DivX, Xvid or Motion-JPEG video paired with MP3 or raw PCM audio, and while old desktop players handle that fine, modern devices largely don't. Drop an AVI into a browser `<video>` tag, a phone's camera roll, an Instagram or WhatsApp upload, or a timeline in Premiere or CapCut, and you'll often get a black screen, a codec error, or silence. MP4 with H.264/AAC is the answer because it is the one combination that plays natively on iPhones, Android, every major browser, smart TVs, social platforms and essentially all editing software. This tool does a genuine transcode rather than a lazy rename: it decodes the AVI's stream, re-encodes the picture to H.264 with a yuv420p pixel format (the profile phones and browsers actually decode), converts the audio to AAC, and writes the MP4 with the moov atom moved to the front (`+faststart`) so it starts playing the instant it loads on the web instead of buffering the whole file first. Drop your AVI, click convert, and the tool works locally: it shows a determinate progress bar and plays the finished MP4 right in the page so you can confirm the picture and sound survived before you save. Because everything is client-side there is no upload wait and no privacy tradeoff: old family recordings, archived screen captures, ripped footage and internal clips never leave your machine, and there is no server to store, log or leak them. Be honest with yourself about speed: single-threaded WebAssembly FFmpeg is meaningfully slower than a native encoder, and AVIs are frequently large and only lightly compressed, so a short clip converts in seconds while a long or high-resolution file takes real time and leans on your browser tab's memory. When you have an AVI that simply won't play where you need it to, drop it here and get a modern MP4 back that just works, entirely in the browser.
- Difficulty:
- Medium
- Typical time:
- ~1–2m
- Processing:
- 100% browser processing
- Converts:
- AVI → MP4
Last updated
How to use the avi to mp4
- 1
Drop your AVI
Drag an AVI onto the workspace, or click to browse. The clip is probed locally for its duration and dimensions. Nothing is uploaded.
- 2
Convert to MP4
Click Convert AVI to MP4. FFmpeg loads once (a one-time download), then a progress bar tracks the H.264 encode as it runs on your device.
- 3
Preview the result
The finished MP4 plays right in the page with its exact file size, so you can confirm the picture and sound survived the transcode.
- 4
Download or restart
Save the MP4, or reset and drop another AVI to convert the next file in your batch.
What AVI to MP4 includes
Real H.264/AAC MP4 output
Your AVI's DivX/Xvid/MJPEG video is re-encoded to H.264 and its audio to AAC inside a proper MP4, a genuine transcode with yuv420p pixels, not a renamed.avi that still won't play.
Plays everywhere
MP4 with H.264/AAC is the one combination iPhones, Android, every major browser, smart TVs, social apps and editors decode natively, the exact reason an AVI wouldn't open in the first place.
Web-ready faststart
The MP4 is written with its moov atom moved to the front (+faststart), so it begins playing the instant it loads on a web page instead of buffering the whole file first.
Handles legacy codecs
Old AVIs are usually DivX, Xvid or Motion-JPEG with MP3 or PCM audio. FFmpeg decodes those legacy streams and re-encodes them into the modern H.264/AAC stack cleanly.
Preview before you download
The finished MP4 plays right in the tool with its exact file size, so you can confirm the picture and audio came through before you save or share it.
100% in your browser
FFmpeg runs as WebAssembly on your device. Your AVI is never uploaded, stored or logged, safe for old personal recordings, archived footage and private captures.
Why use our avi to mp4
Make a stubborn AVI finally play
An AVI that shows a black screen or a codec error on your phone, in a browser or in an editor becomes a clean H.264 MP4 that opens on all of them: converted locally, without emailing it to yourself or hunting for an old player.
Get it onto social and the web
Instagram, WhatsApp, TikTok and most upload forms reject or mangle AVI. Transcode to MP4 on-device and hand them exactly the format they accept, with faststart so it streams instantly.
Rescue old footage privately
Unlike upload-based converters, nothing leaves your machine. A decades-old family AVI or an internal recording is re-encoded on-device, so no server ever sees your archive.
No install, no watermark, no sign-up
Get a real H.264/AAC MP4 without desktop software, a login or a stamped-on logo: just a browser tab you can close when you're done.
Built for the way you work
From quick one-off fixes to daily workflows, see how people put this tool to use.
- Anyone with old footage
Play a legacy AVI on a phone
Convert a DivX/Xvid AVI from an old camcorder or download into an H.264 MP4 that opens straight from your iPhone or Android photos app. No obscure player, no upload to a random site.
- Social / Content creator
Get an AVI onto Instagram or TikTok
Social platforms reject or garble AVI. Transcode to MP4 on-device and upload the format they actually accept, with faststart so it starts instantly on feed.
- Video editor
Import into a modern timeline
Some editors choke on old AVI codecs. Re-encode to a clean H.264 MP4 so it drops into Premiere, DaVinci or CapCut without a transcode-on-import stall: done privately before the project even opens.
- Archivist / IT
Modernize an archive of AVIs
Bring 1990s-2000s AVI recordings up to a future-proof MP4 that today's players and browsers decode natively, one file at a time, without any of the footage leaving the machine.
Supported formats
Accepts AVI, and produces MP4, all processed locally in your browser.
- AVI
- MP4
Frequently asked questions
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Common problems, solved
Hit a snag? Here are quick fixes for the issues people run into most.
The conversion is slow.
Single-threaded WebAssembly FFmpeg is much slower than a native encoder, and AVIs are often large and lightly compressed, which makes them the heavy case. Trim to just the part you need first, close other heavy tabs, and expect real time for long or high-resolution files.
It ran out of memory or the tab crashed on a big AVI.
Uncompressed or very long AVIs can exhaust a browser tab's memory. Try converting on a desktop browser with more RAM, close other tabs, or split the AVI and convert it in parts. As a loose guide, keep source files under a few hundred MB.
The audio is missing in the MP4.
Some old AVIs carry an unusual or non-standard audio codec that couldn't be decoded to AAC. The video will still convert. If sound matters and dropped out, the source audio stream is likely the culprit. Try extracting or re-recording the audio separately.
Nothing happens on the first click / there's a pause before progress.
The first conversion downloads the FFmpeg WebAssembly core (~31 MB) once, then caches it. Give it a moment on the first run. Later conversions in the same session start immediately.
Get the most out of it
Trim to just the seconds you need before converting, encode time scales with length, so a shorter clip finishes far faster.
AVIs are often big and lightly compressed, so the MP4 will usually come out much smaller, a nice bonus on top of the compatibility win.
Convert on a desktop browser with a bit of RAM headroom. Large AVIs are memory-bound in single-threaded WASM.
If you only need a smaller file rather than a format change, the Video Compressor gives you a direct quality dial instead.
Keep the original AVI until you've previewed the MP4 and confirmed the picture and audio both survived.
What's new
Recent updates and improvements to the avi to mp4.
Initial release: browser-side AVI-to-MP4 conversion via WebAssembly FFmpeg, re-encoding video to H.264 and audio to AAC with yuv420p and +faststart, plus a live progress bar, in-page preview and download. Nothing is uploaded.
Added a before/after size delta on the result and clearer guidance for legacy DivX/Xvid sources and non-standard audio streams.
Sharpened the honest notes on single-threaded WASM encode speed and memory limits for large, lightly-compressed AVI files, and improved handling of missing-audio edge cases.
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Your privacy is built in
Your AVI is decoded and re-encoded to MP4 entirely in your browser using FFmpeg compiled to WebAssembly. It is never uploaded to any server. Nothing is stored, logged or transmitted, so you can safely convert old family recordings, archived footage and private captures. The FFmpeg core is fetched once from this site (same-origin) and cached. Your media stays on your device. Close the tab and every trace is gone.
- Runs in your browser
- No uploads
- Nothing stored
Ready to try the avi to mp4?
Free, private and instant. AVI to MP4 runs right in your browser.