WebM to MP4 Converter

How to Use the WebM to MP4 Converter

Three steps, all in your browser.

1. 1

   Load your WebM

   Drag a .webm file onto the box or click to pick one. WebM is common from screen recorders and the web.

2. 2

   Convert to MP4

   Click Convert. The VP8/VP9 video is re-encoded to H.264 and the audio to AAC in an MP4 container.

3. 3

   Download the MP4

   Preview and download the .mp4 — ready for video editors, messaging apps and sites that don’t accept WebM.

Which codec is inside your WebM, and what changes when it becomes an MP4?

WebM is not one format — it is a restricted Matroska profile with four common payloads.

Transparency. VP8 and VP9 can carry an alpha channel in WebM — that is how transparent web animations are shipped. H.264 has no alpha, so anything transparent is flattened, usually to black, the moment it becomes an MP4. If you need transparency in an Apple or Adobe pipeline, the target is ProRes 4444 in a .mov, not an MP4.

Frame timing. WebM files produced by a browser’s MediaRecorder — which is what almost every in-browser screen recorder uses — are variable frame rate, and many carry no reliable duration in the header at all. Converting to a constant-frame-rate MP4 can shift the reported length, or drift audio against picture over a long recording. Split a long screen capture into segments with the Video Trimmer rather than converting an hour in one pass.

Audio. Opus at 96 kbps is roughly equivalent to AAC at 128 kbps, and this tool writes AAC at 160 kbps, so you will not hear the difference. It is still a re-encode rather than a copy — one unavoidable generation of loss, because no Apple or Adobe product imports Opus.