The stored frame's height in pixels.
The message kind.
The encoded image's height, computed on the room's thread.
The encoded image's width, computed on the room's thread (upright, then capped for the source's kind).
The frame's packed I420 planes (Y, then U, then V): a copy the host owns, in the transfer list.
JPEG quality, 1-100 (clamped by the worker).
Increasing per host; echoed in the reply.
Clockwise rotation the frame needs to stand upright.
The stored frame's width in pixels.
One sampled frame to scale, rotate and encode.