Click to choose an MP4 or drop it here
MP4 in, WebM out — converted in your browser, never uploaded. MOV and other video types work too.Video and audio are processed in your browser by FFmpeg (ffmpeg.wasm), free software under the GPL-2.0-or-later and MIT licenses — licenses & source.
About converting MP4 to WebM
To convert MP4 to WebM, drop your .mp4 file on the box above, pick a quality, and press Convert to WebM. The page encodes the picture as VP8 and the sound as Vorbis, the open formats of the WebM family, and gives you a .webm file to download.
People need WebM for web pages (an HTML5 <video> with a WebM source), for some website builders and game engines, for animated stickers and short loops, and for any place that asks for an open, royalty-free video format.
Everything runs in your browser. Your video is never uploaded.
Features
- MP4 in, WebM out — VP8 video and Vorbis sound
- Three quality levels with a clear bitrate limit, so you know the file size
- Optional resize — 1080p, 720p or 480p for a smaller, faster file
- Rotated phone videos come out upright
- Preview before you save — play the WebM on the page, then download it
- Private — no upload, no sign-up, no watermark
What is WebM?
WebM is a video format that Google started in 2010 for the open web. The container is a simple version of Matroska (MKV). Inside go open, royalty-free codecs: VP8, VP9 or AV1 for the picture, and Vorbis or Opus for the sound.
Chrome, Firefox, Edge and Opera play WebM, and Safari on the Mac plays it since 2021. On iPhones and in many video editors, MP4 is still the safer choice. That is why many web pages offer both: a WebM and an MP4 of the same video.
MP4 or WebM?
| MP4 (H.264 + AAC) | WebM (VP8 + Vorbis, from this page) | |
|---|---|---|
| Chrome, Firefox, Edge | Yes | Yes |
| Safari on Mac | Yes | Yes (since 2021) |
| iPhone and iPad | Yes | Not everywhere — keep an MP4 too |
| Video editors, TVs, phones' galleries | Almost all | Some |
| Royalty-free codecs | No (patents on H.264, AAC) | Yes |
| Transparent video (alpha) | No | Possible with VP8/VP9 (not made by this page) |
Use WebM when a website, a web player or a tool asks for it, or when you want an open format. Keep the MP4 for phones, editors and sending to people.
File size: what each quality gives
The page encodes VP8 with a quality target and a bitrate limit, and the sound as Vorbis at about 128 kbps. So the file is never bigger than about the limit, and calm or simple video often comes out smaller:
| Quality | Video limit | Size per minute, at most about | 10 seconds | 5 minutes |
|---|---|---|---|---|
| High | 2 Mbps | 16.0 MB | 2.7 MB | 80 MB |
| Good | 1 Mbps | 8.5 MB | 1.4 MB | 42 MB |
| Smaller | 600 kbps | 5.5 MB | 0.9 MB | 27 MB |
The numbers are (video limit + 128 kbps sound) × seconds ÷ 8. Good is plenty for 720p. For 1080p with lots of movement choose High. For a small background loop on a web page, choose Smaller and 480p.
Why VP8 and Vorbis?
VP9 makes smaller files at the same quality, but it needs much more memory. In the video engine this page runs inside your browser, VP9 stops with a memory error on the first frame. VP8 finishes, and every browser that plays WebM plays VP8. A slightly bigger file that works is better than a smaller one that never finishes.
The same goes for the sound: Vorbis works in this engine, the Opus encoder does not. Every player that plays WebM plays Vorbis.
How long does it take?
The encoder runs inside your browser on one processor core, set to its fast mode. For 720p, expect about as long as the video, or a little less: in our test a 20-second 720p phone clip took 15 seconds on a laptop. 1080p takes about twice as long, and a phone is slower. Choosing 720p or 480p makes it faster. You can switch tabs while it works; keep this one open.
Frequently asked questions
How do I convert MP4 to WebM for free?
Drop the MP4 on the box above, keep Good quality, and press Convert to WebM. When it is done, play the result and press Download WebM. There is no sign-up, no watermark and no upload.
Will the WebM be smaller than my MP4?
Often, because the page sets a bitrate limit: 1 Mbps at Good. A phone MP4 is usually 10–20 Mbps, so its WebM is much smaller (and a little softer). A small, already-compressed MP4 may come out about the same size.
How do I use the WebM on my website?
Put both files in a <video> tag, WebM first and MP4 second: <source src="clip.webm" type="video/webm"> and then <source src="clip.mp4" type="video/mp4">. Each browser plays the first one it can.
Can I make a WebM with a transparent background?
Not with this page. VP8 and VP9 can carry transparency, but a normal MP4 has no transparent parts to keep.
Are subtitles kept?
No. The WebM holds the picture and the first sound track. To show text in the video, burn it in first with Add Subtitles to Video.
Is my video uploaded?
No. The converter (ffmpeg) runs inside your browser, on your device. The video never leaves it.
Related tools
- WebM to MP4 — the other way, for phones and editors
- Video Converter — MP4, WebM or MKV from many formats
- MP4 to GIF — a GIF loop for places that do not take video
- Resize Video — change the resolution before converting
- Trim Video — keep only the part for your page
Credits
Conversion is powered by ffmpeg.wasm (FFmpeg, libvpx and libvorbis).
How to use it
- Click the box and choose your MP4, or drag it onto the box
- Choose the Quality — *Good* is right for most videos
- Choose a smaller Resolution for a smaller, faster file
- Press Convert to WebM and wait — the first time also loads the video engine
- Play the result, then press Download WebM
