Choose a WebM
Select a WebM containing a codec supported by the bundled FFmpeg build.
Convert WebM to MP4 Online
Turn a WebM file into a broadly compatible H.264/AAC MP4. Conversion runs entirely on your device.
Local video tool
Choose a WebM video
Choose a video
or drag and drop
WebM video · up to 250 MB
How it works
Convert locally
VP8, VP9, or other readable video is transcoded to H.264; readable audio becomes AAC.
Download MP4
Preview the broadly compatible result and download it with the original filename stem.
Why WebM needs transcoding
WebM commonly contains VP8, VP9, or AV1 video plus Opus or Vorbis audio. Those streams cannot be assumed to work inside a conventional MP4, so this tool transcodes rather than blindly copying them.
The standard FFmpeg.wasm build supports many common combinations but not every codec. Unsupported or corrupted files return a clear error and are never uploaded as a fallback.
Frequently asked questions
Can WebM be renamed to MP4?
No. Renaming does not convert the internal video and audio streams. This tool creates a real H.264/AAC MP4.
Will conversion reduce quality?
Transcoding can introduce a small quality change. It is required for broad MP4 compatibility.
Which WebM codecs work?
Common VP8/VP9 and Opus/Vorbis combinations work when supported by the bundled FFmpeg.wasm core. AV1 support can vary.
Is the WebM uploaded?
No. It is read and converted in the browser worker.