Convert MP4 to WebM for the web
This MP4 to WebM converter turns MP4 videos into WebM — the open, royalty-free format designed for HTML5 video — entirely in your browser. Most MP4s contain H.264 video and AAC audio, which WebM can’t hold, so the video is re-encoded to VP9 (or AV1, if you prefer) and the audio to Opus, using the encoders built into your browser.
Web developers use WebM for background videos, product loops and self-hosted clips, often next to an MP4 fallback. VP9 and AV1 usually reach the same visual quality as H.264 with fewer bits, which means lighter pages. And if your MP4 already contains VP9 or AV1 with Opus, as many downloads do, the streams are simply copied into WebM without re-encoding.
How to use the MP4 to WebM Converter
- Add one or more MP4 files.
- Choose the Video codec. VP9 is the default — quick to encode and played by every major browser. AV1 is smaller still but slower and only offered where your browser can encode it; VP8 suits very old players.
- Optionally limit the Resolution — 720p or 1080p is plenty for most web pages — and pick a Quality.
- Press Convert to WebM. Encoding takes roughly as long as the video plays, often less on a recent computer.
- Preview the WebM next to the original, then download it or the whole batch as a ZIP.
MP4 to WebM Converter features
VP9, AV1 or VP8
Pick the codec that suits your audience; anything your browser can’t encode is marked unavailable instead of failing halfway.
Opus audio
AAC and MP3 soundtracks are re-encoded to Opus, the IETF-standard codec (RFC 6716) that WebM players expect.
Lossless when possible
MP4s holding VP9 or AV1 with Opus are rewrapped as WebM in seconds.
Scale while converting
Cap the size at 1080p, 720p, 480p or 360p in the same pass — ideal for hero and background videos.
Runs locally
No upload queue and no server-side size cap; your device’s encoders do the work.
What WebM is
Google announced WebM in May 2010 as a royalty-free format for the open web. The container is a restricted profile of Matroska; the first codecs were VP8 video and Vorbis audio, later joined by Opus (2012), VP9 (2013) and AV1 (2018, from the Alliance for Open Media). Because the codec list is short and free of royalties, every major browser engine implements it.
Chrome, Edge, Firefox and Opera play WebM natively, as do Android and many smart TVs. Recent Safari versions play many WebM files, but QuickTime, the iPhone Photos app and most editing software don’t open WebM at all — which is why websites usually offer WebM first and MP4 as a fallback.
Putting a WebM on your website
List the WebM first and an MP4 second inside one <video> element, so each browser picks the first file it can play: <source src="clip.webm" type="video/webm"> followed by <source src="clip.mp4" type="video/mp4">. For silent background loops add the muted, autoplay, loop and playsinline attributes — browsers only autoplay video that is muted.
Keep hero videos short and light: 720p at Medium quality is usually enough behind text, and the WebM compressor can trim the size further. A WebM loop is typically many times smaller than the same clip as a GIF; if you need a GIF anyway, use Video to GIF.
VP9, AV1 or VP8?
| Codec | File size | Encoding speed | Plays in |
|---|---|---|---|
| VP9 | Small | Moderate to fast | All current browsers; recent Safari |
| AV1 | Smallest | Slower, and needs browser support | Current Chrome, Edge and Firefox; Safari on Apple devices with AV1 hardware |
| VP8 | Largest of the three | Fast | Practically every WebM player, old ones included |
MP4 to WebM Converter FAQ
How do I convert MP4 to WebM?
Drop the MP4 above, keep VP9 or pick AV1, and press Convert to WebM. The video and audio are re-encoded in your browser and the WebM is ready to download when the progress bar finishes.
Why does MP4 to WebM take longer than other conversions?
WebM can’t contain H.264 or AAC, so every frame has to be decoded and encoded again. Only MP4s that already hold VP9 or AV1 with Opus can be rewrapped instantly.
Is WebM smaller than MP4?
Usually, at the same visual quality, because VP9 and AV1 compress more efficiently than H.264. The saving depends on the content and the quality setting.
Does WebM play on an iPhone?
Recent iOS versions play many WebM files in Safari, but the Photos app and many other iPhone apps don’t. For anything going to Apple devices, keep an MP4 copy.
Can a WebM have a transparent background?
WebM with VP9 can store transparency, but MP4 sources have no alpha channel, so a converted MP4 stays opaque.
Is my video uploaded to a server?
No. Encoding happens on your device through the browser’s WebCodecs encoders, driven by the Mediabunny library (MPL-2.0).