I had the same question, but I imagine that the "media pipeline" box with a line that goes directly from "compositor" to "encoder" is probably hiding quite a lot of complexity

Recall's offering allows you to get "audio, video, transcripts, and metadata" from video calls -- again, total conjecture, but I imagine they do need to decode into raw format in order to split out all these end-products (and then re-encode for a video recording specifically.)