The SDK's VideoBufferType.I420 value: a frame in another buffer type is converted to it first, on the caller's thread.
Cap on the encoded image's longer side, in pixels. The image is never enlarged.
JPEG quality, 1-100 (clamped).
Clockwise rotation the frame needs for upright display (WebRTC's convention).
How a watcher asks for one sampled frame to be encoded.