MP4 to WebM

Re-encode an MP4 file as a WebM container with VP9 video and Opus audio. WebM is the open, royalty-free format used by YouTube and most browsers — great for embedding video on the web with small file sizes. The conversion runs locally via ffmpeg.wasm, so your video never leaves your device. Performance depends on your CPU: expect roughly real-time encoding for short clips (a 5-minute 720p video may take 1–2 minutes to convert). Very large files or 4K sources may be slow or run out of memory — for best results keep inputs under about 500 MB.