Known for maintaining high quality and offering granular settings for resolution and file size.
Open VLC, go to Media > Convert/Save , add your MP4, and select a WebM profile.
A versatile tool that supports over 1,000 formats and allows for batch conversion. How to get it: Available via the MiniTool Download Page.
A simple, fast web-based tool for quick one-off conversions. Summary of Popular Downloadable Tools
Drag your MP4 into the app, select "WebM" under the Summary tab, and click "Start Encode".