Free converter · Lossy re-encode
Convert AVI to MP4
Short answer
Drop your AVI file into the converter below and download the MP4 file. It runs in your browser with FFmpeg, for files up to 100 MB; nothing is uploaded. The file is re-encoded to H.264 video and AAC audio in MP4, at FFmpeg's default quality, with the source's sample rate. Re-encoding takes longer than a container swap and costs some quality; how much depends on the clip and on the quality setting, and at the converter's default setting the loss can be visible, so keep the original.
Maximum file size: 100 MB. The first conversion loads a ~30 MB converter engine, once per visit. Nothing is uploaded - conversion runs on your device.
Re-encode to H.264/AAC for modern players. · Lossy re-encode · Browser-side via FFmpeg WASM - nothing uploaded.
Key takeaways
- The 7.89 MB AVI file was re-encoded and became 3.81 MB (-51.7%).
- The result holds: Video: h264 1920x1080; Audio: aac 48000 Hz 2 ch.
- In your browser the same conversion of a 3 second clip took 28.0 seconds on the single-thread engine; natively, the 10 second clip took 4.7 seconds.
- The picture scored SSIM 0.998 against the source (1.0 would be identical).
- Next to it: AVI to AAC (-97.9%), AVI to FLAC (-79.8%), AVI to GIF (+676%).
Measured: AVI to MP4
The converter's own ffmpeg arguments, run on a 10 second 1920 × 1080 excerpt of Big Buck Bunny (an animated film, not camera footage) saved in AVI. The browser column is the same arguments on the single-thread WebAssembly core with a 3 second excerpt, in a headless run; your device will differ. Results describe this clip and these encoders.
| Check | Result |
|---|---|
| Mode | Re-encoded |
| Input | AVI, 7.89 MB |
| Output | MP4, 3.81 MB (-51.7%) |
| Output streams | Video: h264 1920x1080; Audio: aac 48000 Hz 2 ch |
| Time, native, 10 s clip | 4.7 s |
| Time, browser engine, 3 s clip | 28.0 s |
| Picture similarity (SSIM) | 0.998 |
A re-encode decodes and encodes every frame or sample, so the time grows with the length of the file.
AVI vs MP4
| AVI | MP4 | |
|---|---|---|
| Full name | Audio Video Interleave (Microsoft) | MPEG-4 Part 14 |
| What is inside | Older codecs such as MPEG-4 Part 2 (DivX, Xvid) with MP3 audio | H.264 or H.265 video with AAC audio |
| Compression | Depends on the codec inside | Depends on the codec inside |
| Best for | Old Windows software and media players that need it | Uploading anywhere: the format social platforms document first |
What you get
H.264 video and AAC audio in MP4, at FFmpeg's default quality, with the source's sample rate. Re-encode to H.264/AAC for modern players.
Planning a bigger file
These are estimates scaled up from the 10 second clip. Real files differ with content, resolution and bitrate, so treat them as an order of magnitude, not a promise.
| Length of the video or recording | Input size (like ours) | MP4 size | Time in your browser |
|---|---|---|---|
| 1 minute | 47.19 MB | 22.80 MB | 9.3 minutes |
| 10 minutes | 471.86 MB | 228.03 MB | 93 minutes |
| 1 hour | 2831.16 MB | 1368.19 MB | 560 minutes |
An AVI file of this kind reaches the 100 MB limit of the converter after about 2.2 minutes; converting it would take roughly 21 minutes on the single-thread engine, and the MP4 would be about 50.67 MB.
AVI and MP4 next to their neighbors
The same clip through other conversions with the same source or the same target.
| Conversion | How | Size change | Time (native) |
|---|---|---|---|
| AVI to MP4 | Re-encode | -51.7% | 4.7 s |
| AVI to AAC | Re-encode | -97.9% | 0.30 s |
| AVI to FLAC | Re-encode | -79.8% | 0.11 s |
| AVI to GIF | Re-encode | +676% | 5.4 s |
| AVI to M4A | Re-encode | -97.9% | 0.31 s |
| AVI to MKV | Re-encode | -51.7% | 4.7 s |
| AVI to MOV | Re-encode | -51.7% | 4.7 s |
Choosing MP4
MP4: MPEG-4 Part 14. Uploading anywhere: the format social platforms document first. AVI: Audio Video Interleave (Microsoft). Old Windows software and media players that need it.
- Keep your original: a re-encode is a copy of a copy.
- If the destination states the format it accepts, use that and nothing else.
Questions people ask
Is this AVI to MP4 converter free and private?
Yes. It is free, needs no account and runs entirely in your browser, so the file never leaves your device.
Will converting AVI to MP4 reduce quality?
Some, because MP4 is depends on the codec inside and the file is re-encoded. How much depends on the clip and on the quality setting, and at the converter's default setting the loss can be visible, so keep the original. For uploads, the platform re-encodes again anyway.
Is there a file size limit?
Files up to 100 MB. The first conversion downloads a converter engine of about 30 MB once per visit; larger files are better handled by a desktop app such as HandBrake or FFmpeg.
How do I convert AVI to MP4?
Choose the file in the converter above and download the MP4. It runs in your browser with no upload.
Will converting AVI to MP4 reduce quality?
A little. The picture scored SSIM 0.998 against the source in our test.
Why did the file size change by -51.7%?
The target codec and settings decide the size. This 10 second clip came out at 3.81 MB.
How long does it take?
A 3 second clip took 28.0 seconds in the browser engine in our test; time grows with the length of the file.
How long will an AVI file of 100 MB take?
At the speed we measured in the browser engine, about 21 minutes for a file like our clip. Your device and the content will change it.
Is my file uploaded?
No. The conversion runs in your browser.
Is there a size limit?
Files up to 100 MB. The first conversion downloads a converter engine of about 30 MB once per visit.
More converters
Sources and how we checked
- MDN: Media container formats
- MDN: Web audio codec guide
- MDN: Image file type and format guide
- FFmpeg documentation: stream copy
- FFmpeg Documentation: ffmpeg (stream selection, -map, -c copy) (read 2026-10-09)
- MDN: Media container formats (read 2026-10-09)
- Blender Foundation: Big Buck Bunny (CC BY 3.0), the clip used for the measurements (read 2026-10-09)
Reviewed October 8, 2026. What the converter writes was measured with ffprobe on the same FFmpeg build your browser downloads; format descriptions follow MDN's media guides.