Convert WebM to MP4

It re-encodes to H.264, which involves a small quality trade-off like any re-compression, but at the default settings it is visually close to the source. The upside is a file that plays everywhere MP4 is expected.

No. The transcode runs with WebCodecs on your own device, so the video never leaves the browser — no account, no quota, no size limit. Chrome, Edge and Firefox work best; Safari’s video encoding is more limited.

WebM is a web-first container built around the VP8, VP9 or AV1 codecs — great in browsers, but many phones, video editors and social upload forms never added support for it. The file is fine; the format is simply outside what that software reads. Converting to an H.264 MP4 puts the same video into the container almost every device and app accepts.

The audio inside a WebM is usually Opus or Vorbis; the tool re-encodes it to AAC to sit alongside the H.264 video, which is what a standard MP4 uses. So the converted file plays with sound on devices that would not have handled the WebM original audio codec. A WebM with no audio track simply becomes a video-only MP4.

Yes — there is no limit on how many you convert or how large they are, since everything runs in your browser rather than on a server. Each file is transcoded on your own machine, so a batch just takes proportionally longer. Converting to H.264 is a re-encode, so it is technically lossy, but at the tool quality setting a single pass is hard to distinguish from the source.