>>311212319
VRC already tracks the viseme as a parameter with the name "Viseme" and uses the Oculus numbers for tracking them, so you can use this as a guide for the transitions. It'll go in the FX layer since it'll be primarily blendshapes (unless you have lip bones, but that seems pretty above and beyond).
You'll also want to make the transitions have no exit time and a rather short duration so your mouth doesn't move too slowly as well as get stuck in a list of visemes to go through.
Finally in the Avatar Descriptor you'll want to set the Lip Sync Mode to "Viseme Parameter Only" so then you won't have them playing over each other, but the parameter will still be tracked.