WEBM is video the way browsers like it: open, royalty-free and built to stream. It was born in 2010, Google, out of its VP8 acquisition, and its real weak spot is life outside the browser: editors, TVs and Apple devices get picky.
OGG is the free spirit of audio: open, patent-free, and quietly brilliant at looping game sound. A container usually carrying Vorbis or Opus audio, both open and royalty-free. That makes it the right destination when what you need is games and open projects that want seamless loops and zero licensing strings.