Free tool
MP4 to WebM converter
This MP4 to WebM converter re-encodes an MP4’s H.264 video as VP9 and its AAC sound as Opus, the WebM pair every current browser plays. It runs in your browser with its own encoders: a 30-second 720p clip took a few seconds.
- Free
- VP9 video, Opus sound
- Nothing is uploaded
Drop your MP4 video here, or Choose your MP4 video
MP4, MOV, WebM or MKV, up to 2 GB and 3 hours. Everything happens in your browser; nothing is uploaded.
How it works
How do you convert MP4 to WebM?
Add the MP4 and press Convert to WebM. Each frame is decoded and encoded again as VP9 by your browser, and the sound becomes Opus. When it finishes, the WebM plays in the page so you can check it before downloading.
- 1
Add the MP4
An export from your editor, a screen recording, a clip for your website.
- 2
Convert to WebM
A bar shows the progress; our 5½-minute 720p video took 24 seconds in Chrome’s engine.
- 3
Download the WebM
Same name with .webm, same picture size and length.
When is WebM better than MP4?
On your own web pages. VP9 and Opus are royalty-free and VP9 usually gives a smaller file than H.264 at the same quality, so a page can offer a WebM first and the MP4 after it. Outside browsers, MP4 is the safer choice: many apps don’t open WebM.
- 1
Offer both
Put the WebM first and the MP4 second inside your video element; each browser plays the first one it can.
- 2
Keep the MP4
It’s the copy for email, phones, editors and every app that doesn’t read WebM.
- 3
Add captions
A WebVTT file in a track element shows captions over either one.
Is the WebM smaller than the MP4?
Usually, at the same look. The converter aims VP9 at somewhat less data than the H.264 it replaces, because VP9 needs less for the same picture. How much smaller depends on the video: busy, grainy footage gains less than a screen recording.
Why VP9 and not VP8 or AV1?
VP9 is the WebM codec that Chrome, Edge and Safari all play and can encode, and it beats the older VP8 on size. AV1 is smaller still, but slow to encode in a browser and older phones can’t decode it, so it’s not used here.
Do your videos need captions?
If they’re recorded talks, lessons or interviews, yes, and you can make them on your Mac. NoteOwl transcribes a recording on-device and exports SRT subtitles; the SRT to VTT converter turns them into captions for a web page.
FAQ
Questions about converting MP4 to WebM
Is my MP4 uploaded?
No. The page reads the MP4 from your device and encodes the WebM itself. In our tests no network request left the page while it converted, and there’s no account.
Does Safari play WebM?
Yes, current Safari on a Mac plays VP9 and Opus in WebM. The WebM this page made played in both browser engines we tested, Safari’s and Chrome’s; for older Apple devices, keep the MP4 as a second source.
How long does it take?
Our 30-second 720p clip took 2.3 seconds in Chrome’s engine and 4.1 in Safari’s on a Mac with Apple silicon, and a 5½-minute one 24 and 32 seconds. Sharper videos take longer; keep the tab open until it finishes.
Can it make a WebM without sound?
If the MP4 has no sound, the WebM has none either. To take the sound out of one that does, use the remove audio from video tool first, then convert.
Will the WebM keep the MP4’s quality?
It’s a re-encode, so it’s a new picture, made at a bitrate chosen for its size and frame rate to look the same. Compare them in the page before you save.
Can I convert WebM back to MP4?
Yes, with the WebM to MP4 converter, which re-encodes VP9 back to H.264. Keep your original MP4 if you have it: converting back and forth loses a little each time.
Keep exploring
More video tools
- Video compressorMake a video smaller in your browser: pick a size to fit (10, 25 or 100 MB, or your own) or a quality, and see the size before and after
- Video trimmerTrim the start and end off a video in your browser with handles over its frames; copied without re-encoding, or cut on the exact frame
- Remove audio from videoTake the sound out of an MP4, MOV, WebM or MKV in your browser; the picture is copied as it is, so it keeps its quality
- Video converterConvert a video to MP4, WebM or MOV in your browser; streams that already fit are copied in seconds, the rest re-encoded with the browser’s own encoders
Related
- SRT to VTT converterConvert SRT to VTT, VTT to SRT, or either to clean text with each speaker’s lines merged, in your browser; Zoom and Teams transcripts work
- Video to textTurn video to text free: drop in an MP4, MOV, M4V, MKV or WebM video and get an AI transcript with times, as text, SRT, VTT or Word; only the sound is sent, nothing is stored
- Export your notesExport meetings, dictations and notes as Markdown or PDF, imported transcripts as text or SRT, or everything as plain files; nothing is locked in
Captions for your recordings, made on your Mac
Free to download. Runs entirely on your Mac.
macOS 26 or later · Apple Silicon (M1 or newer) · 16 GB memory minimum, 24 GB recommended
About NoteOwl
NoteOwl is private AI meeting notes and memory for the Mac. It captures meetings without a bot joining the call, labels every speaker, writes summaries and action items, and builds a memory of every conversation that you can chat with — fully offline, because the speech recognition and the AI run on the Mac itself. Dictation into any app is free; Pro is a one-time purchase.
NoteOwl pricing: what’s free and what Pro adds
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