WebM with VP9 + Opus is the open, royalty-free format used by YouTube and modern browsers. It delivers about 50% smaller files than equivalent H.264 MP4s at the same visual quality, which is great for websites and bandwidth-conscious delivery.

What do the quality presets mean?

High uses VP9 CRF 31 (best quality, larger file). Balanced uses CRF 35 (good quality, half the size). Small uses CRF 40 (heavy compression, smallest output — fine for previews and casual sharing).

Will WebM play everywhere?

WebM plays natively in Chrome, Firefox, Edge, Opera and modern Android. Safari on iOS 17.4+ also supports it. For older Safari or legacy hardware, stick with MP4 via our to-MP4 converter .

Why is VP9 encoding so slow?

VP9 trades encoding time for compression efficiency — that is how it produces such small files. Expect roughly real-time encoding for short clips on a modern desktop. Trim long videos first to stay reasonable.

Is the audio quality good?

Opus is widely regarded as the best lossy audio codec available — it sounds better than MP3 at every bitrate and is the default voice codec for Discord, WhatsApp and YouTube.

Is my video uploaded?

No. ffmpeg.wasm runs locally in your browser. Your file never leaves your device.

Convert to WebM — VP9 + Opus in Browser

Convert Video to WebM

Convert MP4, MOV, AVI or MKV to WebM (VP9 + Opus) — entirely in your browser, no upload.

100% client-side · no upload

Video file (MP4, MOV, AVI, MKV…)

Load a video file to begin.

How to convert a video to WebM

Load your video file — MP4, MOV, AVI and MKV all work.
Pick a quality preset: High for archival, Balanced for the web, Small for short previews.
Click Convert to WebM and wait for VP9 + Opus encoding to finish.
Download the resulting .webm file.

Common use cases

Website hero videos: Self-hosted WebM is up to half the size of MP4 — faster page loads.
HTML5 video tags: Provide a WebM variant alongside MP4 in <source> for the best modern-browser quality.
Bandwidth-conscious sharing: Send a smaller WebM over Discord, Telegram or Slack when MP4 hits size limits.
Open-format archive: Keep recordings in royalty-free VP9 + Opus instead of patent-encumbered H.264 + AAC.

Related tools: Convert to MP4 · Video Compressor · Video Trimmer · Video Resizer

よくある質問

Why convert to WebM?: WebM with VP9 + Opus is the open, royalty-free format used by YouTube and modern browsers. It delivers about 50% smaller files than equivalent H.264 MP4s at the same visual quality, which is great for websites and bandwidth-conscious delivery.
What do the quality presets mean?: High uses VP9 CRF 31 (best quality, larger file). Balanced uses CRF 35 (good quality, half the size). Small uses CRF 40 (heavy compression, smallest output — fine for previews and casual sharing).
Will WebM play everywhere?: WebM plays natively in Chrome, Firefox, Edge, Opera and modern Android. Safari on iOS 17.4+ also supports it. For older Safari or legacy hardware, stick with MP4 via our <a href="/video/to-mp4/">to-MP4 converter</a>.
Why is VP9 encoding so slow?: VP9 trades encoding time for compression efficiency — that is how it produces such small files. Expect roughly real-time encoding for short clips on a modern desktop. Trim long videos first to stay reasonable.
Is the audio quality good?: Opus is widely regarded as the best lossy audio codec available — it sounds better than MP3 at every bitrate and is the default voice codec for Discord, WhatsApp and YouTube.
Is my video uploaded?: No. ffmpeg.wasm runs locally in your browser. Your file never leaves your device.