Convert MP4 to WebM With VP9 Video and Opus Audio, No Upload
Re-encode an MP4 to VP9 and Opus WebM at Good, Better or Best quality. Runs in your browser, no upload.
Drag & drop a video, or
MP4, MOV, MKV, AVI, WebM supported
Higher quality means a larger file.
A free MP4 to WebM converter that runs on your device
This MP4 to WebM converter re-encodes your MP4 into a WebM file with VP9 video and Opus audio. Drop in the MP4, pick Good, Better or Best, and download the WebM. The whole conversion runs in your browser on your own computer or phone, and I don't cap file size or the number of files you convert.
When it finishes you can play the WebM right on the page before you download it. That's a quick way to check it looks right, because any modern browser plays VP9.
How to convert MP4 to WebM
1.Add your MP4
Drag the file into the tool above, or click to browse for it.
2.Pick a quality level
Good, Better or Best. The bitrate scales with your video's resolution and frame rate, so a higher tier gives a bigger file that stays closer to the source.
3.Convert and download
The video is re-encoded on your device. Preview the WebM on the page, then download it.
The converter uses your browser's WebCodecs encoder when the browser can encode VP9 itself, which is fast. If it can't, the tool falls back to FFmpeg compiled to WebAssembly. That path is slower but produces the same kind of file, and it still runs locally.
MP4 vs. WebM: two containers, different codecs
MP4 and WebM are both containers. A container holds the video, audio and metadata and keeps them in sync. It doesn't decide how the picture itself is compressed; the codec inside does that.
MP4 (MPEG-4 Part 14) is the ISO-standard container that grew out of Apple's QuickTime format. In practice almost every MP4 carries H.264 video, more and more often H.265, with AAC audio. WebM is based on Matroska (MKV) and was built for royalty-free web codecs: VP8, VP9 or AV1 video with Opus or Vorbis audio. It arrived alongside HTML5 video as an open alternative to licensed codecs, which is why it accepts fewer codecs than MP4 on purpose.
Neither format beats the other in general. MP4 plays on nearly everything, while WebM was built for license-free video on web pages.
Why convert MP4 to WebM?
- Video on your own website. An HTML5
<video>element plays WebM natively in every current browser, with no licensed codec involved. - Browser-based workflows. Many screen recorders, browser editors and web apps use WebM as their native format.
- Royalty-free codecs. VP9 and Opus carry no licensing fees, which matters for some projects and platforms.
- A destination that asks for WebM. Some CMSs, game engines and upload forms only accept it.
If the video is going into a traditional editor, onto social media or to a TV, keep it as MP4. H.264 support in those places is close to universal, and VP9 isn't.
What's inside the WebM you get
"WebM" only names the container, so two WebM files can hold very different streams. Here's what exists and what this tool picks:
| Codec | Type | Notes |
|---|---|---|
| VP8 | Video | WebM's original codec from 2010. Still plays, but newer codecs compress much better. |
| VP9 | Video | Google's successor to VP8 and the most common WebM codec today. This converter outputs VP9. |
| AV1 | Video | Newer and more efficient, but far slower to encode and less consistently supported on older devices. |
| Opus | Audio | Modern codec that sounds good across a wide bitrate range. This converter pairs it with VP9. |
| Vorbis | Audio | WebM's original audio codec, mostly replaced by Opus. |
I chose VP9 with Opus because that pair plays in Chrome, Edge, Firefox and Safari today and encodes at a reasonable speed in a browser tab. AV1 would squeeze out a little more efficiency, but on a normal laptop it can take many times longer.
Does converting MP4 to WebM lower the quality?
A little. H.264 already threw away some detail when the MP4 was made, and re-encoding into VP9 is a second lossy pass. Conversion can't bring back what the first encode discarded; a higher WebM bitrate only protects what's left.
At a sensible bitrate, one re-encode is hard to spot. What decides the result is bitrate, resolution and the source's own quality, far more than the codec name. A VP9 file at a low bitrate can look worse than its H.264 source, and one encoded generously can look almost identical. That's why the tool gives you three tiers instead of one fixed setting: Best keeps you closest to the original, Good keeps the file lighter.
Always convert from the best copy you have. A second lossy pass makes any damage from earlier heavy compression more visible.
Is WebM smaller than MP4?
Not automatically. VP9 can match H.264's quality at a lower bitrate, but the file size you get depends on the bitrate and settings actually used, plus the resolution, frame rate, length and how busy the footage is. A generously encoded WebM can end up bigger than the MP4 it came from.
Renaming video.mp4 to video.webm doesn't convert anything either. The streams inside still have to be decoded and encoded again into codecs WebM allows, which is the work this tool does. If what you really want is a smaller MP4, use the video compressor instead.
WebM on websites
In an HTML5 <video> element, the browser plays the first source it can decode. Sites that care about every device often list two sources, a WebM and an MP4, and let each browser choose. VP9 WebM plays in every current desktop and mobile browser, including Safari. AV1 support still varies by browser version and hardware, which is one more reason this tool sticks with VP9.
A few habits give better results for web video: match the resolution to the size the video will actually display at, keep the source frame rate, pick a higher tier for footage with fast motion or fine detail, and test the file on the devices your visitors use.
Frequently asked questions
How do I convert MP4 to WebM?
Drop your MP4 into the tool above, choose Good, Better or Best, and convert. Your browser decodes the video and audio, re-encodes them as VP9 and Opus, and packages them as a WebM file.
Is WebM better than MP4?
Neither is better everywhere. WebM uses royalty-free codecs and suits web pages. MP4 plays on more editors, devices and platforms. Pick the one your destination expects.
Why won't my WebM file play?
Usually the player doesn't support the codec inside the file, like AV1 in an older browser. This tool outputs VP9 and Opus, which every current browser plays. Some older desktop players and TVs don't handle WebM at all; use MP4 for those.
Why is my WebM bigger than the MP4?
Output size comes from bitrate and resolution, not from the container. Pick a lower quality tier for a lighter file.
Why does my WebM have no sound?
The source MP4 probably had no audio track. Many screen recordings don't. If the MP4 plays with sound but the WebM is silent, let me know through the contact page.
Why is the conversion slow?
VP9 does more work per frame than H.264, so it takes longer to encode, and your own device is doing it. Browsers without a native VP9 encoder use the slower WebAssembly fallback. Keep the tab in the foreground while it runs.
Can I just rename .mp4 to .webm?
No. Renaming doesn't change the container or the codecs, and most players will refuse the mislabeled file. The video has to be re-encoded.
What codec does WebM use?
WebM can hold VP8, VP9 or AV1 video with Opus or Vorbis audio. This converter writes VP9 video and Opus audio.
Is my video uploaded anywhere?
No. Your device decodes the MP4 and encodes the WebM inside the browser tab, so the file isn't sent anywhere.
Can I convert to other formats?
Yes. For old players and editing software there's an MP4 to AVI converter, and to keep only the sound there's an MP4 to MP3 converter.