Are my files uploaded to a server?

No. This conversion runs inside your browser using your own device’s processing power, and the file is not uploaded. Once a tool has been used once (video, text recognition and background removal download their engine from this site the first time), it keeps working when your connection drops.

Why won’t my editor accept WebM?

WebM uses VP8/VP9, which many editors never implemented. H.264 in an MP4 is a widely supported interchange format.

Does the file get bigger?

Often slightly, since VP9 compresses a little better than H.264 at the same quality. The compress tool can bring it back down to a size you choose.

Convert WebM to MP4

Runs on your device · Your file never leaves your device.

WebM plays in browsers but is rejected by many video editors, phones and social platforms. MP4 is far more widely supported.

The video is re-encoded to H.264 with AAC audio, which is the combination those tools expect.

Conversion runs on your device, so nothing is uploaded and there is no queue to wait in.

How to convert WebM to MP4

Add your WebM file — typically a screen recording or a web download.
Press Convert to re-encode it to H.264 in an MP4 container.
Download a file that opens in editors and on phones.

Supported formats and limits

Input: WebM (VP8, VP9 or AV1)
Output: MP4 (H.264)
Why convert: WebM plays in browsers but is refused by many editors and devices
Quality: Re-encoded at settings that keep the difference hard to see
Where it runs: In your browser; nothing uploaded

Not for: Keeping the smallest possible file — VP9 in WebM is often more efficient than H.264; convert only when you need compatibility.

What is inside a WebM, and what changes

A WebM holds VP8, VP9 or AV1 picture with Opus or Vorbis sound. Neither sound format is one this tool copies into an MP4, so the sound is always converted to AAC at 128 kbit/s, and the picture is encoded again as H.264. WebM is a web format, so the browser can usually decode it and your device's own video encoder does the work.

VP8 and VP9 can carry a transparent background, as some animation and overlay exports do. H.264 in an MP4 has no transparency, so the MP4 is a solid picture. Keep the WebM wherever the transparent background matters.

AV1 files

A WebM can also hold AV1. Where the browser decodes AV1, your device’s own encoder reads the file directly, as it does VP9. Only the built-in engine needs help, because it has no working AV1 decoder: when it has to do the job, the browser’s decoder first steps through the video frame by frame and rebuilds the picture as H.264, with the sound carried across, while the progress line counts the frames. That is an extra pass over the whole file, made only when the engine needs it.

The tool stops only if the browser cannot decode AV1 either, and says so. A current version of Chrome, Edge or Firefox decodes AV1, and the site uses that decoder automatically.

Screen recordings with no stated length

Recordings made inside a browser, by screen-capture extensions and some meeting tools, are often saved as WebM without their length written into the file. They still convert here, and the MP4 that comes out does carry its length.

That matters for /compress-video, which works out a bitrate from the length. When it cannot read one, it stops and asks for the file to be converted to MP4 first. Converting it on this page is that first step; then compress the MP4.

Frequently asked questions

Are my files uploaded to a server?: No. This conversion runs inside your browser using your own device’s processing power, and the file is not uploaded. Once a tool has been used once (video, text recognition and background removal download their engine from this site the first time), it keeps working when your connection drops.
Why won’t my editor accept WebM?: WebM uses VP8/VP9, which many editors never implemented. H.264 in an MP4 is a widely supported interchange format.
Does the file get bigger?: Often slightly, since VP9 compresses a little better than H.264 at the same quality. The compress tool can bring it back down to a size you choose.