Free converter · Lossy re-encode
Convert WebM to AVI
Short answer
Drop your WebM file into the converter below and download the AVI file. It runs in your browser with FFmpeg, for files up to 100 MB; nothing is uploaded. The file is re-encoded to MPEG-4 Part 2 video and MP3 audio in AVI. 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.
VP8/Opus re-encoded to legacy AVI codecs. · Lossy re-encode · Browser-side via FFmpeg WASM - nothing uploaded.
Key takeaways
- The 2.11 MB WebM file was re-encoded and became 2.64 MB (+25.1%).
- The result holds: Video: mpeg4 1920x1080; Audio: mp3 48000 Hz 2 ch.
- In your browser the same conversion of a 3 second clip took 3.2 seconds on the single-thread engine; natively, the 10 second clip took 1.5 seconds.
- The picture scored SSIM 0.975 against the source (1.0 would be identical).
- Next to it: WebM to AAC (-92.2%), WebM to FLAC (-24.0%), WebM to M4A (-92.3%).
Measured: WebM to AVI
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 WebM. 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 | WebM, 2.11 MB |
| Output | AVI, 2.64 MB (+25.1%) |
| Output streams | Video: mpeg4 1920x1080; Audio: mp3 48000 Hz 2 ch |
| Time, native, 10 s clip | 1.5 s |
| Time, browser engine, 3 s clip | 3.2 s |
| Picture similarity (SSIM) | 0.975 |
A re-encode decodes and encodes every frame or sample, so the time grows with the length of the file.
WebM vs AVI
| WebM | AVI | |
|---|---|---|
| Full name | WebM (open web format) | Audio Video Interleave (Microsoft) |
| What is inside | VP8, VP9 or AV1 video with Vorbis or Opus audio | Older codecs such as MPEG-4 Part 2 (DivX, Xvid) with MP3 audio |
| Compression | Lossy | Depends on the codec inside |
| Best for | Video on web pages; YouTube accepts it, most short-form apps do not | Old Windows software and media players that need it |
What you get
MPEG-4 Part 2 video and MP3 audio in AVI. VP8/Opus re-encoded to legacy AVI codecs.
Where you can upload AVI
| Platform | AVI | What the platform documents |
|---|---|---|
| TikTok | Not accepted | AVI is not listed for TikTok Content Posting API uploads. |
| Instagram Reels | Not documented | AVI is not in Instagram's published video specs, which list MOV and MP4. Convert to MP4 before uploading. |
| Instagram Feed | Not documented | AVI is not in Instagram's published video specs, which list MOV and MP4. Convert to MP4 before uploading. |
| YouTube Shorts | Accepted | Yes - AVI is listed among YouTube supported upload formats. |
| Facebook Reels | Unclear | Current AVI support for Facebook video uploads has not been reverified. |
| Accepted | Yes - LinkedIn lists AVI for organic video on desktop, iOS and Android. |
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) | AVI size | Time in your browser |
|---|---|---|---|
| 1 minute | 12.60 MB | 15.76 MB | 64 seconds |
| 10 minutes | 125.97 MB | 157.64 MB | 11 minutes |
| 1 hour | 755.83 MB | 945.83 MB | 64 minutes |
A WebM file of this kind reaches the 100 MB limit of the converter after about 8.3 minutes; converting it would take roughly 8.8 minutes on the single-thread engine, and the AVI would be about 131.22 MB.
WebM and AVI next to their neighbors
The same clip through other conversions with the same source or the same target.
| Conversion | How | Size change | Time (native) |
|---|---|---|---|
| WebM to AVI | Re-encode | +25.1% | 1.5 s |
| WebM to AAC | Re-encode | -92.2% | 0.32 s |
| WebM to FLAC | Re-encode | -24.0% | 0.13 s |
| WebM to M4A | Re-encode | -92.3% | 0.31 s |
| WebM to MKV | Re-encode | +51.6% | 5.0 s |
| WebM to MOV | Re-encode | +51.9% | 5.1 s |
| WebM to MP3 | Re-encode | -92.4% | 0.25 s |
Choosing AVI
AVI: Audio Video Interleave (Microsoft). Old Windows software and media players that need it. WebM: WebM (open web format). Video on web pages; YouTube accepts it, most short-form apps do not.
- 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 WebM to AVI 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 WebM to AVI reduce quality?
Some, because AVI 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 WebM to AVI?
Choose the file in the converter above and download the AVI. It runs in your browser with no upload.
Will converting WebM to AVI reduce quality?
A little. The picture scored SSIM 0.975 against the source in our test.
Why did the file size change by +25.1%?
The target codec and settings decide the size. This 10 second clip came out at 2.64 MB.
How long does it take?
A 3 second clip took 3.2 seconds in the browser engine in our test; time grows with the length of the file.
How long will a WebM file of 100 MB take?
At the speed we measured in the browser engine, about 8.8 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.