How much smaller is WebM than MP4?

For typical content WebM with VP9 is 20–35% smaller than H.264 MP4 at matching visual quality. Talking-head and screen-recording footage often hits the upper end of that range.

Does WebM play on iPhone?

Safari has supported WebM since iOS 14.5 / macOS Big Sur. Older iOS devices may fail to play it inline — if your audience includes iOS 13 and below, ship MP4 alongside.

Will the audio quality drop?

vexo encodes WebM audio with Opus, which is one of the best codecs available. At default settings most listeners cannot tell the difference from the source AAC.

Is this video converter free?

Yes. vexo is free to use, no account is required, and there are no paid plans.

Are my videos uploaded to a server?

No. vexo runs entirely in your browser using ffmpeg compiled to WebAssembly. Your videos are never uploaded, never seen by our infrastructure, and never stored anywhere outside your device. When you close the tab, every file is gone.

Which formats are supported?

Inputs: MP4, MOV, WebM, MKV, AVI, MPEG, 3GP, OGV and GIF. Outputs: MP4 (H.264 + AAC), WebM (VP9 + Opus) and animated GIF.

Why does the first conversion take a moment?

The first time you convert a video, vexo downloads the conversion engine (about 25 MB). After that it stays in your browser cache, and subsequent conversions start immediately.

Is there a file size limit?

Yes. Each file may be up to 200 MB. Browser memory is the real ceiling — very large 4K clips may struggle on lower-end devices.

Can I trim or resize the video?

Yes. You can set a start/end time to trim and pick a target width (1080p, 720p, 480p, 360p or original).

How long does a conversion take?

Depends on the video. A 1-minute 1080p MP4 typically converts in 1–3 minutes on a modern laptop. Mobile is slower. The progress bar shows real-time progress.

Why is my converted file bigger than the original?

If you raise the quality slider above the source's encoder settings, the output can grow. Lower the slider toward 50–70 for noticeable shrink, or trim/resize to drop the bitrate further.

Can I convert multiple videos at once?

Not yet. Video encoding is memory-heavy, so vexo converts one file at a time. Batch support may come later.

Are ads required to use the tool?

No. Ads are isolated from the converter. The tool works completely even if ads fail to load or are blocked.

MP4 → WebM

Convert MP4 to WebM

WebM (VP9 + Opus) gives you smaller files than MP4 at the same perceived quality, perfect for HTML5 video on the modern web. Drop your MP4 below and vexo re-encodes it to WebM directly in your browser — nothing is uploaded.

Drop your video here

or choose a file from your device

Choose video

MP4

MOV

WebM

MKV

AVI

GIF

Max 200 MB per file. Conversion runs in your browser.

Every conversion runs entirely in your browser. Your video never leaves your device.

About MP4 → WebM

Why convert MP4 to WebM?

WebM with VP9 typically produces 20–35% smaller files than H.264 MP4 at the same visual quality. For HTML5 <video> elements served from your own site, that means faster page loads, lower CDN bills and better Core Web Vitals. Every modern browser plays WebM natively.

What's the right quality setting?

Around 70 is a sensible default. Drop to 50–60 for thumbnails or short loops where size matters more than fidelity; push to 85+ for hero videos. The quality slider maps to VP9's CRF internally, so the trade-off is well-tuned.

Is my MP4 uploaded anywhere?

No. vexo loads ffmpeg compiled to WebAssembly into your browser and runs the transcode locally. The file never leaves your device, and closing the tab erases everything.

What you're converting between

A short primer on both formats so the trade-offs are obvious before you hit Convert.

MP4

Source

MPEG-4 Part 14 · introduced 2001

H.264 + AAC

MP4 is the default video container of the modern web. With H.264 video and AAC audio it is the format every iPhone, Android phone, Windows machine, Mac, smart TV, video editor, social platform and browser understands without extra codecs. vexo encodes MP4 with the H.264 'veryfast' preset and 128 kbps stereo AAC — a safe default for talking-head, music and screen recordings.

Strengths

Plays on every device and player on Earth
Hardware-decoded on phones and laptops
Compact at quality 70–80 for most content

Trade-offs

Slightly larger than WebM at the same perceived quality
H.264 has licensing concerns for some use cases (not for end-users)

WebM

Target

WebM · introduced 2010

VP9 + Opus

WebM was designed for the open web. VP9 typically produces 20–35% smaller files than H.264 MP4 at the same visual quality, and Opus is the best general-purpose audio codec available. Every modern browser (Chrome, Firefox, Safari 14+, Edge) plays WebM natively. vexo encodes WebM with VP9 + Opus, and falls back to VP8 + Vorbis automatically if the wasm bundle lacks VP9.

Strengths

Smaller files than MP4 at the same perceived quality
Royalty-free, open codec
Native playback in every modern browser

Trade-offs

Older video editors (iMovie, older Premiere) may reject it
Some social uploaders and legacy players prefer MP4
Slower to encode than MP4 in ffmpeg-wasm

Each link below opens the converter pre-tuned for that conversion.

Supported formats

MP4 is the safest default for web and mobile playback. WebM gives the smallest files for modern browsers. GIF is for short, soundless animations.

WMV, FLV and other legacy/streaming formats are not supported in this version. Please convert those to MP4 first using a desktop tool.

Format	Input	Output	Notes
MP4	Yes	Yes	H.264 + AAC, broadest compatibility
MOV	Yes	No	Apple/QuickTime container; convert to MP4
WebM	Yes	Yes	VP9 + Opus, smaller than MP4
MKV	Yes	No	Container; convert to MP4 or WebM
AVI	Yes	No	Legacy container; convert to MP4
GIF	Yes	Yes	No audio, short clips only
WMV	No	No	Not supported
FLV	No	No	Not supported

Frequently asked questions

Your videos never leave your device

vexo is a static page. Every conversion runs inside your browser via ffmpeg compiled to WebAssembly. There is no server-side processing, no upload, no temporary file, no cache. When you close this tab, every file is gone.

No account required.
No server processing. Your videos stay on your device.
No caching, no Service Worker, no IndexedDB persistence.
The conversion engine (ffmpeg-wasm) is fetched from a public CDN and cached by the browser; no personal data is sent.

Convert MP4 to WebM

About MP4 → WebM

Why convert MP4 to WebM?

What's the right quality setting?

Is my MP4 uploaded anywhere?

What you're converting between

MP4

Strengths

Trade-offs

WebM

Strengths

Trade-offs

Popular conversions

Supported formats

Frequently asked questions

How much smaller is WebM than MP4?

Does WebM play on iPhone?

Will the audio quality drop?

Is this video converter free?

Are my videos uploaded to a server?

Which formats are supported?

Why does the first conversion take a moment?

Is there a file size limit?

Can I trim or resize the video?

How long does a conversion take?

Why is my converted file bigger than the original?

Can I convert multiple videos at once?

Are ads required to use the tool?

Your videos never leave your device