Convert MP4 to WebM
To convert MP4 to WebM, add your .mp4 file below and press the button: it's processed on your own device and you download the result, with nothing uploaded. It's free, needs no account, and works with files up to 500MB.
About converting MP4 to WebM
MP4 (.mp4) files can be converted to WebM entirely in your browser — no software to install, no file upload, and no account required. The conversion runs on a WebAssembly build of ffmpeg directly on your device.
Technical comparison
| MP4 | WebM | |
|---|---|---|
| Category | video | video |
| Compression type | Lossy (H.264/H.265 video, AAC audio) | Lossy (VP8/VP9/AV1 video, Vorbis/Opus audio) |
| Typical file size | Moderate — a few MB per minute of 1080p video, varying with CRF/bitrate | Small to moderate — typically smaller than an equivalent MP4 at the same quality |
| Transparency support | No | Yes (VP8/VP9 support an alpha channel) |
How to convert MP4 to WebM privately
Every step below runs on a WebAssembly build of ffmpeg inside this browser tab. Your .mp4 file is never uploaded to a server — there's no network request carrying it anywhere.
Add your MP4 file
Drag and drop, or click to select, a file (.mp4). It's read straight from disk into browser memory — no upload step exists.
Convert locally
FreePrivateConvert converts it to WebM using a WebAssembly build of ffmpeg, entirely within this browser tab.
Download the result
Save your converted .webm file. It only ever existed in this tab's memory — closing the tab without downloading discards it completely.
Convert MP4 to WebM with ffmpeg (command line)
Prefer the terminal? This is the exact ffmpeg command this page runs for you:
ffmpeg -i input.mp4 -c:v libvpx -crf 10 -b:v 2M -c:a libopus output.webm- -i input.mp4
- Your MP4 file.
- -c:v libvpx
- Encode the video as VP8, the original WebM video codec, supported by every WebM player.
- -crf 10
- Quality level for VP8 (4-63, lower = better quality; 10 is high quality). Works with -b:v below as a bitrate ceiling.
- -b:v 2M
- Maximum video bitrate of 2Mbit/s, so busy scenes can't balloon the file size.
- -c:a libopus
- Encode the audio as Opus, the standard audio codec for WebM.
- output.webm
- The WebM file to create. ffmpeg picks the container from this extension.
Don't have ffmpeg installed? You don't need it: use the converter at the top of this page. It runs the same conversion on your own device, and your file is never uploaded.
FAQ
- Is my file uploaded anywhere?
- No. Your file is read and processed inside this browser tab and never leaves your device. You can confirm it in your browser's developer tools: the Network tab shows no upload.
- Does converting MP4 to WebM reduce quality?
- The video is re-encoded as VP8 (CRF 10, capped at 2 Mbit/s) with Opus audio. Quality is good for most clips, but the bitrate cap can soften high-resolution or fast-moving video.
- Is there a file size limit?
- Yes: 500MB per file. There's no account and no limit on how many files you convert.
- What's the difference between MP4 and WebM?
- MP4 (MPEG-4 Part 14) and WebM store data differently. MP4: lossy (H.264/H.265 video, AAC audio). WebM: lossy (VP8/VP9/AV1 video, Vorbis/Opus audio). WebM is an open, royalty-free video container built specifically for the web, pairing VP8/VP9/AV1 video with Vorbis/Opus audio.
- Why convert MP4 to WebM?
- Common uses for WebM: Web video without codec licensing costs; Bandwidth-constrained streaming; Progressive web apps. Open, royalty-free codec stack with no licensing fees, unlike H.264/HEVC.
- What MIME type does a .webm file use?
- video/webm, the standard type for WebM.
- What is the ffmpeg command to convert MP4 to WebM?
- Run: ffmpeg -i input.mp4 -c:v libvpx -crf 10 -b:v 2M -c:a libopus output.webm. This is the exact command FreePrivateConvert runs for this conversion, so you can use this page instead of installing ffmpeg: it runs the same conversion inside your browser.
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