Convert a video between MP4 and WebM locally in your browser - using your browser codecs. The video never leaves your device. No upload.
Running locally on your device ...
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Your files never left your device
No. Everything runs in your browser - your file never leaves your device. How this is verifiable
MP4 with H.264 is the universally compatible video format: it runs on almost any device, in every editing program and on every platform. WebM with VP9, on the other hand, is lean, royalty-free and ideal for embedding in web pages. Depending on where the video needs to go, a program or service wants exactly one or the other - this tool converts between the two containers.
You only choose the target format. The tool decodes the video and re-encodes it into the matching codec of the target container (MP4 uses H.264, WebM uses VP9), using your browser native encoder through WebCodecs. The resolution stays unchanged; if you also want to shrink it, use the sibling tool "Compress video". An audio track is carried over as long as a matching audio codec can be encoded.
As with all tools here, the conversion happens strictly locally in your browser - the video is not uploaded and no codec library is loaded from a foreign server. Because it is re-encoded, the conversion is lossy and not a lossless repackage. There are deliberately no GPL codecs: only the encoders your browser ships with are used.
| Input formats | MP4, M4V, WEBM, MOV, MKV |
|---|---|
| Output format | MP4 |
| Batch processing | No |
| Processing | Locally in your browser (WebCodecs) |
| File upload | None |
Limitations: Converting re-encodes lossily; it is not a lossless repackage of the stream. It needs a modern browser with WebCodecs; if that is missing, you get an honest message instead of a silent failure. MP4 uses H.264, WebM uses VP9. An audio track is carried over if its codec can be encoded, otherwise it is dropped.
No. The conversion runs entirely locally in the browser; the video does not leave your device.
MP4 (H.264) is compatible everywhere - the safe choice. WebM (VP9) is leaner and royalty-free, ideal for the web.
No. The video is re-encoded, which is lossy. This tool is not meant for a pure repackage without re-encoding.
A modern browser with WebCodecs (recent Chrome, Edge or Safari). Without support you get a clear message.