The format is only read at the start of the recording. (It’s a constraint of the underlying macOS framework we’re using for movie recording, AVFoundation.) Hm, we should mention format in the node’s documentation, in the paragraph about “Certain characteristics of the movie are determined when saving starts, and can’t be changed while saving is in progress…”
Were you just experimenting, or was there something specific you wanted to use variable bitrate for?
Apple had some videos at WWDC 2017 about their new H265 compression and streaming etc they stepping it up, but needs latest hardware CPUs I think. Just trying to think if any streaming software I’ve used can change bit rate on the fly? I don’t think so…
I have not tested this at all, but maybe you could record a series of 1-frame movies each with a different bitrate (use the Finalize port to end one movie and start the next) and then assemble them back into one movie using a composition like the attached.