Convert AVI to MP4 in your browser
This AVI to MP4 converter turns AVI files — clips from an old digital camera, a dashcam, a 2000s download or a screen recorder — into MP4 files that play on phones, smart TVs, WhatsApp, YouTube and every browser. It opens the AVI on your own device, reads which codecs are inside, and then picks the gentlest way to make an MP4: copy the video untouched where possible, re-encode it only where it has to.
The same .avi extension can hold very different video. H.264 only needs a new wrapper, so it is remuxed in seconds with no quality loss; Motion JPEG is encoded as H.264 by your browser; Xvid and DivX go through FFmpeg, downloaded only after you agree. The page shows which path it will take, and why, before you convert.
How to use the AVI to MP4 Converter
- Drop your AVI onto the box above or click it to choose a file. The page lists its duration, resolution, frame rate, codecs and size.
- Read the coloured label: Lossless remux, Re-encode with WebCodecs or FFmpeg (WebAssembly), with a sentence explaining the choice.
- Optionally choose Sound → Remove sound, a lower Quality when re-encoding for a smaller file, or — for Xvid and DivX — whether to keep the MPEG-4 video as it is.
- Press Convert AVI to MP4 (or Download converter (32 MB) & convert on the FFmpeg path). A progress bar shows the percentage; Cancel stops at any time.
- Compare the original and the new MP4 side by side, check the size and time taken, and press Download MP4.
AVI to MP4 Converter features
Lossless remux for H.264
H.264 frames, MP3 and AAC sound are copied packet for packet. B-frame order, which AVI never records, is rebuilt from each frame’s picture order count.
Motion JPEG to H.264
Camera clips in Motion JPEG with PCM sound become H.264 with AAC, usually several times smaller.
Xvid and DivX through FFmpeg
MPEG-4 Part 2, DivX 3, Cinepak, Indeo, DV and other legacy codecs are converted by ffmpeg.wasm, downloaded once on request.
Large and damaged files
OpenDML AVIs over 1 GB are read segment by segment, and corrupt areas are skipped instead of stopping the conversion.
Private by design
The video is read straight from your disk into the page. Nothing is uploaded, and there is no watermark or sign-up.
What happens to your AVI
The converter looks at the actual codecs inside the file, not just the extension, and treats each stream separately:
| Inside the AVI | How it becomes MP4 | Quality |
|---|---|---|
| H.264 video (x264, AVC1) | Copied into the MP4 (remux) | Identical to the AVI |
| Motion JPEG (camera clips) | Decoded and encoded as H.264 with WebCodecs | High; file usually much smaller |
| Xvid, DivX 4–6 (MPEG-4 Part 2) | FFmpeg: re-encoded to H.264, or kept as MPEG-4 | Near-identical, or identical |
| DivX 3, Cinepak, Indeo, DV, WMV | FFmpeg: re-encoded to H.264 | Near-identical |
| MP3 or AAC sound | Copied | Identical |
| PCM (uncompressed) sound | Encoded to AAC | Transparent at the default quality |
| AC-3, MP2, ADPCM, GSM sound | FFmpeg: encoded to AAC — or removed | Near-identical |
Why AVI files often refuse to play
AVI (Audio Video Interleave) dates from Microsoft’s Video for Windows in 1992. No web browser plays it, and most phones and streaming boxes ignore it. Often the codec is the bigger problem: Xvid and DivX, the standard for sharing video in the 2000s, use MPEG-4 Part 2, which browsers and modern hardware decoders dropped. MP4 (ISO/IEC 14496-14) with H.264 video and AAC sound plays on practically every device made in the last fifteen years.
Keeping Xvid as is is lossless and fast, and the result plays in VLC and on many TVs, but not in Chrome, Safari or the iPhone Photos app. Choose Convert to H.264 when the file needs to play everywhere.
Tips for the best result
- If only the sound is in an unusual format, Remove sound lets the video be copied instantly without the 32 MB converter.
- The FFmpeg converter runs on one CPU core, so a long Xvid film can take as long as its running time. Short clips finish in seconds.
- Need a smaller file afterwards? Use the video compressor, or make an animation with MP4 to GIF. Old Flash or phone videos: FLV to MP4 and 3GP to MP4.
The software behind it
Reading the AVI structure (the RIFF movi list and OpenDML extensions) and rebuilding H.264 frame order is done by code written for this page. MP4 files are written by Mediabunny (MPL-2.0), encoding uses your browser’s WebCodecs API, and the optional converter is ffmpeg.wasm (FFmpeg, GPL-2.0-or-later), loaded unmodified into its own worker only when you ask for it.
AVI to MP4 Converter FAQ
How do I convert AVI to MP4 without losing quality?
If the AVI contains H.264 video, this AVI to MP4 converter copies it into the MP4 without re-encoding, so the quality is identical. For Xvid or DivX files choose MPEG-4 video → Keep as is for a lossless copy, at the cost of playback on browsers and iPhones.
Is my video uploaded anywhere?
No. The file is read directly by your browser and converted on your device. Only the program code — Mediabunny, and FFmpeg if you ask for it — is downloaded from a public CDN.
Why does the page offer to download a 32 MB converter?
Browsers have no decoder for codecs such as Xvid, DivX, Cinepak or ADPCM sound. FFmpeg compiled to WebAssembly can decode them; it is 32 MB, so the page asks first, and your browser keeps a cached copy for next time.
Why is the MP4 smaller (or bigger) than my AVI?
A remux keeps the same video data, so the size barely changes. Motion JPEG and uncompressed AVIs shrink a lot when encoded as H.264. Re-encoding a heavily compressed Xvid at High quality can come out slightly larger; pick Medium or Small file to trim it.
Will the MP4 play on my iPhone, Android phone or TV?
Yes when the video ends up as H.264 with AAC or MP3 sound, which is the default for every path. The only exception is the optional “Keep as is” setting for MPEG-4 Part 2 video.
Can it convert very large AVI files?
It reads OpenDML AVIs over 1 GB, but the MP4 is built in memory, so a computer handles a couple of gigabytes more comfortably than a phone.
Why does my converted video have no sound?
Either Remove sound was selected, or the AVI had no audio stream. The information table lists the audio codec before you convert, and the result line under the preview says whether the MP4 has sound.