Convert AVI to MP4
Turn old AVI files into MP4s that iPhones, Android phones, TVs and editors play, without uploading them.
- Nothing is uploaded
- Works offline after first visit
- Open source
- No watermark · limit is your device’s memory; phones hold less
Converts AVI videos (Xvid, DivX 4 and later, and Motion JPEG, with MP3, AC-3 or PCM sound) to MP4 with H.264 video and AAC sound. It is free and needs no account, and your videos are not uploaded: everything runs in your browser on your device, and after one visit and a short wait the page works offline.
Done
Free, no ads. Support StayPut
Open the network tab. Your files never appear in it.
Add files and run the tool to see every request this tab makes.
Your files are processed on this device and never sent to a server. Reload the page to clear everything from memory.
AVI is Microsoft’s container from the 1990s, and it is still what many old digital cameras, camcorders, downloaded clips and family DVD rips are saved as. Phones, smart TVs, PowerPoint and most upload forms no longer open it, and browsers cannot play it at all.
This page reads the AVI in your browser, decodes the picture and sound, and writes a new MP4 with H.264 video and AAC sound, the combination that plays everywhere. Unlike a simple rewrap, an AVI always has to be re-encoded, because the video inside (Xvid, DivX, Motion JPEG) is not a format an MP4 player expects. A clip converts at several times its running time or faster on a laptop, and slower on a phone.
The file never leaves your device. Home videos and camera footage are exactly what you should not hand to a stranger’s server just to change the wrapper, and here there is no upload to wait for and no copy kept anywhere.
The picture is re-encoded at a high quality setting, so the MP4 can come out larger than the AVI when the original was heavily compressed. If it is bigger than you want for email or chat, run it through Compress video afterwards.
To go the other way, use MP4 to AVI. The two are separate jobs, each with its own settings.
Which AVI files this converts
- Picture: MPEG-4 video (Xvid, DivX 4 and later, and the MP4V and FMP4 variants) and Motion JPEG, which is what many digital cameras and screen recorders write.
- Sound: MP3, MP2, AC-3 and uncompressed PCM. Surround sound is mixed down to stereo, and low-quality sound is brought up to 48 kHz so every player accepts it.
- Not converted: AVIs whose picture is H.264, DivX 3, Windows Media, VP6 or another codec this page does not carry. The page names the codec it found, so you know what you have.
What this page loads
Most video runs on your browser's WebCodecs through Mediabunny. For old formats the browser cannot read, the page loads a decoder built from FFmpeg's libraries (LGPL) only when you convert such a file.
That decoder is a file of about 2 MB (under 1 MB compressed) from stayput.dev, not from anyone else’s server, and the licenses page links its exact source and how it was built.
How it works
- Drop one or more AVI files, or tap to pick them.
- Tick Remove the sound if you only need the picture.
- Convert, then open or share the MP4. Several files download together as a zip.
In your browser, not on a server
Mediabunny (MPL-2.0), a media toolkit written in TypeScript, reads the MOV, MKV, WebM or MP4 container in your tab. H.264 video and AAC or MP3 sound are copied into the new MP4 packet by packet, which takes seconds and changes nothing in the picture. Other video (VP8, VP9, AV1) is decoded and re-encoded by your browser’s own video encoder through WebCodecs, H.264 where available, and other sound becomes AAC or Opus. An AVI, which no browser opens, is decoded in a background worker by a separate decoder module and re-encoded the same way. An FLV is opened by a small separate reader module, and its H.264 picture is copied into the MP4 as it is. Most video runs on your browser's WebCodecs through Mediabunny. For old formats the browser cannot read, the page loads a decoder built from FFmpeg's libraries (LGPL) only when you convert such a file. The MP4 is written in memory.
Compared with upload-based tools: Online converters upload the whole video just to rewrap it, which can take longer than the conversion itself, cap free files at 100 MB to 1 GB, and keep a copy on their server. Here the file never leaves your device, and a large MOV from your phone converts in seconds because nothing is re-encoded that does not need to be.
Verify it yourself. Give the page a short while after one visit to save itself for offline use, then turn off Wi-Fi or switch to airplane mode and run the tool again. Or open your browser's developer tools (F12, or Cmd-Option-I on a Mac), pick the Network tab, and watch it while you convert. The panel above does the same count for you.
Questions
Why does an AVI take longer to convert than an MKV or MOV?
MOV and MKV files often hold H.264 video that can be copied into an MP4 unchanged. AVI never does, so every frame is decoded and encoded again. Expect roughly five to ten times the clip’s length on a recent laptop for ordinary 480p or 720p video, and keep the tab open until it finishes.
Why does it say the picture is not supported?
AVI is only a wrapper, and many different video codecs live inside it. This page opens Xvid, DivX 4 and later, and Motion JPEG files. An AVI that holds H.264, DivX 3, Windows Media Video or another codec shows a message naming it, and nothing is converted.
Why does the message mention the sound?
The sound inside the AVI is in a format this page cannot decode, such as AAC or Windows Media Audio. Tick Remove the sound to convert the picture alone.
Will the MP4 play on my iPhone and TV?
Yes, when your browser writes H.264, which Chrome, Edge and Safari do; the line under the result names the codec. The MP4 plays in the iPhone Photos app, on Android, on Windows and macOS, and on current smart TVs.
Is the AVI uploaded anywhere?
No. The file is read from your disk in slices by code running in a background worker in your tab, and the MP4 is written in memory. The decoder module downloads from stayput.dev when you first convert, and it carries none of your data.
Can I convert a whole folder of AVI files?
Select them all at once and they are converted one after another; several download together as a zip. Each MP4 keeps the name of its AVI with the new extension.
Is the file uploaded anywhere?
No. There is no server in this process. The page is a static file and the work is done by code running inside your browser tab. Give the page a short while after one visit to save itself for offline use; then you can turn off Wi-Fi and it still works.
More video and audio tools
Video to MP4
Turn MOV, MKV and WebM files into MP4s that play everywhere. Converted on this device, never uploaded.
Trim video
Cut a clip out of a longer video without uploading it. Most cuts take seconds and keep the original quality.
Video splitter
Cut one video into parts at the times you choose, every so often or into equal pieces, and save them in one zip. Done on this device, and the video is not uploaded.
Mute video
Take the sound out of a video, in seconds and without re-encoding. The video never leaves this device.
Other conversions
Guides
- How to convert MOV to MP4MOV plays fine on Apple devices but not everywhere else. Here is how to convert it on a Mac and on Windows.