FFmpeg converter loads on first use (~30 MB, cached after).
Browser compatibility issue
This converter requires SharedArrayBuffer support. Please use Chrome or Edge, or ensure the site is served with
This converter requires SharedArrayBuffer support. Please use Chrome or Edge, or ensure the site is served with
Cross-Origin-Opener-Policy: same-origin and Cross-Origin-Embedder-Policy: require-corp headers.
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Supports .mp4 filesAbout MP4 to WebM conversion
WebM is an open, royalty-free video format developed by Google, optimised for streaming on the web. Converting your MP4 files to WebM using the VP9 codec delivers excellent quality at smaller file sizes — ideal for embedding video on websites and web apps.
This converter uses libvpx-vp9 for video and libopus for audio — the same high-quality codecs used by YouTube and other major platforms. All processing happens locally in your browser; your file is never uploaded anywhere.
Frequently Asked Questions
- Why convert MP4 to WebM?
- WebM offers excellent compression for web delivery, open licensing, and wide browser support. It is the preferred format for HTML5 video elements and progressive web apps.
- Will quality be lost?
- VP9 encoding is highly efficient. At the default CRF 30 setting, most viewers will not notice quality differences compared to the source MP4. Choose CRF 24 for a higher-quality result at a larger file size.
- How long does conversion take?
- It depends on your computer and the video length. A one-minute 1080p video typically takes 1–3 minutes on a modern laptop. FFmpeg.wasm runs on a single thread in the browser, so it is slower than native FFmpeg.
- Is my file private?
- Yes. Conversion happens entirely in your browser — no data is sent to any server.
- What browsers are supported?
- Chrome and Edge work reliably. Recent Firefox versions also work. Safari support depends on the version.