MP4 to WebM converter
Convert MP4 to WebM in your browser. Encodes VP8 video with Vorbis audio — a slower conversion, for reasons explained below.
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Accepts .mp4 · Up to 20 files at a time · up to 667 MB each "Upload" and "download" here mean your browser reading a file from this device and writing one back to it. Nothing is sent to a server — open your browser's network panel and watch: no request carries your file.
FAQ
Why is this so much slower than other conversions?
Because the VP8 encoder in this build only works single-threaded — running it across cores hangs after the first frame. It therefore uses one core while an H.264 encode uses all of them.
Why VP8 and not VP9?
The VP9 encoder in the WebAssembly ffmpeg core crashes on the first frame regardless of settings, and the Opus encoder fails on every input. VP8 with Vorbis is the working combination. Both play in every current browser.
Will the WebM be smaller than the MP4?
Often not. VP8 is roughly a generation behind H.264 in efficiency, and well behind VP9. You are converting for the open format rather than for size.
Do I actually need WebM for the web?
Not for playback — every browser plays MP4 too. Choose WebM when you want to avoid patent-encumbered codecs, or when you are serving both and letting the browser pick.
Is quality lost?
Yes. This is a full re-encode from one lossy codec to another, so some detail goes. Raise the quality preset if the result looks soft; it will be slower and larger.
Is there a size limit?
About 667 MB. Given the speed, a file near that limit will take a long time — start with something short to see the rate on your machine.
Is it really free?
Yes — every conversion on this site, with no account, no watermark and no daily cap. The work happens on your own device, so there is no server bill for us to pass on to you.
Do I need to install anything?
No. It runs in any modern browser, on Windows, macOS, Linux, Android and iOS. There is nothing to download and nothing to sign up for, and once the page has loaded it keeps working with the network switched off.
Related converters
- WebMtoMP4Re-encodes every frame for the new container
- MP4toMOVRepackages the same streams — lossless and near-instant
- MP4toMKVRepackages the same streams — lossless and near-instant
- MP4toAVIRe-encodes every frame for the new container
- MP4toMP3Drops the video, re-encodes the audio to MP3
- MP4toWAVDrops the video, keeps the audio losslessly as WAV
- MP4toAACDrops the video, re-encodes the audio to AAC
- MP4toFLACDrops the video, keeps the audio losslessly as FLAC