MP4 to WebM
MP4 to WebM for a site's video tag, Wikimedia Commons or a forum: VP8 video, Opus audio, three size steps. Free, no sign-up, nothing uploaded.
- Free & unlimited
- No sign-up
- Files never uploaded
- No watermark
- Up to 2 GB per file
How to convert MP4 to WebM
Three steps in a desktop browser. An H.264 or HEVC MP4 is always re-encoded here, so expect it to take about as long as the clip.
- 1
Pick the MP4
Drop an .mp4, .m4v or .mov file on the page. Its size, length and resolution show up before anything is converted.
- 2
Choose Re-encode to set the size
Fast Copy can only copy VP8, VP9 or AV1 video, so an H.264 MP4 is re-encoded either way. Re-encode is where the Quality and Resolution controls appear.
- 3
Convert and save the .webm
The file keeps its name with a .webm ending. The result screen puts the MP4 size next to the WebM size, so you see the difference before you publish.
What goes into the WebM you get
The settings are fixed by what a browser tab can encode quickly and what every modern browser can play.
VP8 video, Opus audio
VP8 with Opus at 128 kbps is a WebM pairing every modern browser plays in a video tag. Visitors need no plugin and no extra codec.
Three quality steps with a ceiling
High, Medium and Small file are VP8 CRF 10, 20 and 32, capped at about 8, 4 and 1.5 Mbps. Small file is the one built for page weight.
Scaling goes down only
Pick 1080p, 720p or 480p, or keep the original. Sizes at or above the source are greyed out, so a 720p clip is never blown up.
Captions kept as WebVTT
Soft text subtitles stored in the MP4 become WebVTT tracks inside the WebM, the caption format of the web.
Speed settings, on purpose
The VP8 encoder runs in its realtime mode because the tab works on one CPU core. That trades some compression for a wait close to the clip's length.
Ways to convert MP4 to WebM, compared
Where the MP4 to WebM encoding happens decides speed, privacy and the codec you end up with.
| This converter | Upload converter sites | HandBrake or FFmpeg | Keep only the MP4 | |
|---|---|---|---|---|
| Where the video goes | Stays in your browser tab | Sent to the service's servers | Stays on your computer | Nowhere |
| Install | None | None | Desktop app or command line | None |
| WebM video codec | VP8 | Varies, often VP9 | VP8, VP9 or AV1 | No WebM |
| Encode speed | About real time at 720p | Depends on the service and your upload | Usually faster, uses every core | n/a |
| Size per file | About 2 GB | Limits depend on the service | Your disk space | n/a |
| Files at once | One | Often several | A queue or a script | n/a |
| Right for | Short web clips, private footage | People fine with uploading | Long videos, smallest files | Sites that accept MP4 |
Where a WebM file earns its place
WebM is a web format first, and these are the jobs where MP4 to WebM is worth the encode.
Hero background loops
A short loop behind a landing page headline. Use Small file at 720p, then set autoplay, muted, loop and playsinline on the tag.
Self-hosted video tags
List the WebM as the first source and the original MP4 as the second. A browser that skips WebM falls back to the MP4.
Wikimedia Commons
Commons is built around open formats such as WebM, so a clip for a Wikipedia article usually needs converting before upload.
Forums and imageboards
Some boards only take WebM attachments. Small file at 480p helps a clip fit a strict upload cap.
Discord chat
Discord plays WebM inline in a channel, so the clip runs right in the conversation.
Docs and changelog demos
Short UI walkthroughs embedded in product docs. Keep them short, since encoding takes about as long as the clip.
Page-weight audits
When an audit flags a heavy video, convert at Small file and compare both sizes on the result screen before you swap anything.
Is WebM smaller than MP4?
Not by default. WebM is a container, and the size comes from the codec inside it. VP9 and AV1 can beat H.264, but this converter writes VP8, an older codec, with fast settings so it can run in a browser tab.
In our own test, a 696 KB H.264 test pattern came out at 2.7 MB as WebM on Medium. Real footage gives a different ratio, but when the MP4 is already well compressed, expect growth more often than savings.
For a lighter file, choose Small file, which caps the video at about 1.5 Mbps, and drop to 720p or 480p. A background loop rarely needs more. If the smallest possible WebM matters more than speed, a desktop encoder with VP9 will do better, just more slowly.
MP4 to WebM mistakes to avoid
Mistake: Expecting the WebM to be smaller than the MP4.
Do this instead: Check both sizes on the result screen. If the WebM grew, convert again with Small file and a lower resolution.
Mistake: Shipping WebM as the only source.
Do this instead: Keep the MP4 as a second source in the video tag. Older Apple devices play MP4 more reliably.
Mistake: Hoping for a transparent background.
Do this instead: H.264 has no alpha channel, and this converter writes VP8 without one. Transparent animations have to be exported from the original project.
Mistake: Picking Re-encode for an AV1 MP4.
Do this instead: This converter has no AV1 decoder, so Re-encode fails on AV1. Fast Copy works instead: WebM can hold AV1 video as it is.
Mistake: Leaving a sound track in a muted hero loop.
Do this instead: Every audio track is kept, with AAC turned into Opus. Add the muted attribute, or remove the audio in an editor if you want those bytes back.
Mistake: Converting a two-hour recording in a tab.
Do this instead: Re-encoding runs at roughly the clip's own length. Trim to the part the page needs, or use a desktop encoder for long videos.
Privacy, cost and limits
Nothing is uploaded
Your file is converted on your own device and is never uploaded to our servers. Picking a file only reads it; conversion starts when you click Convert.
Free, one file at a time
No account, no watermark and no cap on how many videos you convert. There is no batch queue, so files go through one by one.
About 2 GB per file
Browser memory is the ceiling. In our tests a 1.6 GB MKV converted and a 2.1 GB file ran out of memory. Web clips rarely come close.
Open-source engine
FFmpeg 5.1.4 compiled to WebAssembly, with libvpx for VP8. About 32 MB loads from jsDelivr on the first visit and is cached after that.