Convert WebM to MP4
To convert WebM to MP4, add your .webm 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 WebM to MP4
WebM (.webm) files can be converted to MP4 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
| WebM | MP4 | |
|---|---|---|
| Category | video | video |
| Compression type | Lossy (VP8/VP9/AV1 video, Vorbis/Opus audio) | Lossy (H.264/H.265 video, AAC audio) |
| Typical file size | Small to moderate — typically smaller than an equivalent MP4 at the same quality | Moderate — a few MB per minute of 1080p video, varying with CRF/bitrate |
| Transparency support | Yes (VP8/VP9 support an alpha channel) | No |
How to convert WebM to MP4 privately
Every step below runs on a WebAssembly build of ffmpeg inside this browser tab. Your .webm file is never uploaded to a server — there's no network request carrying it anywhere.
Add your WebM file
Drag and drop, or click to select, a file (.webm). It's read straight from disk into browser memory — no upload step exists.
Convert locally
FreePrivateConvert converts it to MP4 using a WebAssembly build of ffmpeg, entirely within this browser tab.
Download the result
Save your converted .mp4 file. It only ever existed in this tab's memory — closing the tab without downloading discards it completely.
Convert WebM to MP4 with ffmpeg (command line)
Prefer the terminal? This is the exact ffmpeg command this page runs for you:
ffmpeg -i input.webm -c:v libx264 -preset veryfast -crf 23 -c:a aac output.mp4- -i input.webm
- Your WebM file.
- -c:v libx264
- Encode the video as H.264, the format virtually every phone, browser and TV plays.
- -preset veryfast
- Encoding speed vs. file size trade-off: veryfast encodes quickly with a slightly larger file.
- -crf 23
- Constant quality level (lower = better quality and bigger file; 18-28 is the usual range, 23 is the default).
- -c:a aac
- Encode the audio as AAC.
- output.mp4
- The MP4 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 WebM to MP4 reduce quality?
- The video is re-encoded as H.264 at CRF 23 (ffmpeg's default quality level, "veryfast" preset) with AAC audio. That looks very close to the source for most footage, but it is a lossy re-encode, so fine detail and grain can soften slightly.
- 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 WebM and MP4?
- WebM and MP4 (MPEG-4 Part 14) store data differently. WebM: lossy (VP8/VP9/AV1 video, Vorbis/Opus audio). MP4: lossy (H.264/H.265 video, AAC audio). MP4 is the default video container for the web and virtually every device — pairs H.264/H.265 video with AAC audio in a single file.
- Why convert WebM to MP4?
- Common uses for MP4: Uploading to YouTube and social platforms; Sharing screen recordings; Web <video> embeds. Near-universal hardware decoding support across phones, browsers, TVs, and game consoles, so playback rarely falls back to slower software decoding.
- What MIME type does a .mp4 file use?
- video/mp4, the standard type for MPEG-4 Part 14.
- What is the ffmpeg command to convert WebM to MP4?
- Run: ffmpeg -i input.webm -c:v libx264 -preset veryfast -crf 23 -c:a aac output.mp4. 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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