Boram is a WebM converter that can do the following:

• Open-source, cross-platform, works on Windows, Mac and Linux
• AV1/VP9/VP8/Opus/Vorbis/2pass/limit/CRF/CQ/raw-args modes support
• Industry-grade codec settings, considered defaults
• Displays almost any video with embedded player, thanks to mpv
• Hardsubbing out of the box with proper shift/track selection
• Simple yet powerful interface, source video centric design
• Multiple encodes at once in single window
• Fast filters result preview, no need to go through trial and error

NOTE: This is an unnofficial wrapper.