What is this MP4 to WebM converter?
A free, browser-based tool that converts a MP4 video to WebM. Add a file, preview it inline, and download the result. All processing happens locally in your browser, so your video is never uploaded and there is no watermark.
Publishing MP4 assets as WebM: the page-weight case
Most published video starts life as an H.264 MP4, because that is what cameras, editors, and stock libraries hand you. For assets that live on your own pages (hero loops, feature demos, background clips) WebM is the web-native delivery format, and camera or editor exports usually carry generous bitrates, so re-encoding at a web-appropriate quality setting typically lands the file well under the original export. How much depends on the footage and the setting. On a video that loads with every pageview, that difference shows up directly in load time and bandwidth bills. The sensible pattern is to serve WebM to browsers that take it and keep the MP4 as the fallback source, not to discard it.
Size versus encode time: the tradeoff you are buying
H.264 is not permitted inside WebM, so this conversion re-encodes the video in full; only an MP4 that already carries AV1 could move over as a straight repackage. Expect the encode to take minutes rather than seconds, growing with resolution and duration. The quality setting is the lever: the high preset preserves the most detail and produces the largest file, the small preset compresses hardest for thumbnails and previews, and the balanced default suits most published assets. Run one representative clip first, compare the output against the source MP4 at full size, then batch the rest with the setting that held up.
How to use it
- Add a MP4 file on the left (drag & drop or click) — it shows an inline preview.
- Pick a quality preset (used only when the video has to be re-encoded).
- Press “Convert & download” to get your WebM file. The first run downloads the ~30MB converter once.
Lossless remux vs re-encoding
MP4 and WebM are containers — what matters is the video codec inside. When the codec already fits WebM, this tool just repackages it (a "remux"): instant and completely lossless. Only when the codec isn't compatible — most often anything involving WebM — does it re-encode the video locally, which takes longer and is where the quality preset applies.