Why is WebM encoding slower than converting to MP4?

VP9 is a more demanding codec and it runs in WebAssembly on your own device. The trade-off is a smaller, open-format file with no upload.

Will audio be preserved?

Yes — the audio track is re-encoded to Opus, WebM's standard audio codec.

Convert MP4 to WebM

Convert MP4 videos to WebM with VP9 video and Opus audio — an open, efficient format ideal for the web. Runs locally in your browser.

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What is WebM?

WebM is an open, royalty-free video container built for the web, pairing VP9 video with Opus audio. Every modern browser plays it natively without plugins.

Why convert MP4 to WebM?

WebM delivers similar quality at a smaller size than H.264 MP4, which is why it is a popular choice for background videos, HTML5 players, and open-source projects.

About encoding speed

Video encoding happens entirely in your browser using WebAssembly. There is no upload and no queue, but that also means your device does the work — expect a large or long clip to take a minute or more. VP9 in particular is compute-heavy, so short clips convert fastest.

How to mp4 to webm

Drop your MP4 file into the zone above.
Press Convert. VP9 encoding runs locally — larger clips take longer.
Download the WebM when the progress bar completes.

Related converters

WebM to MP4Convert WebM videos to MP4 (H.264) for editors and apps that reject WebM.Compress VideoShrink MP4 file size with a quality slider and resolution cap.Video to GIFTurn a clip into a looping GIF with fps and width controls.