Autofocus, set up right
What are the right autofocus settings on the Sony a6400 — Tracking, Eye AF, and animal detection?
Tracking, with its one condition
Set Focus Mode to Continuous AF, then Focus Area to Tracking. Half-press and the camera marks the subject and follows it across the frame; the start area (Wide, Zone, Flexible Spot) is chosen on the Tracking screen. Sony’s guide states the condition plainly: Tracking is available only in Continuous AF, and only for stills — the Tracking area cannot be selected while shooting movies.
Whose eyes?
Set Face/Eye Priority in AF to On, then Subject Detection to match the subject: Human, or Animal. For animals the guide is exact — it detects animal eyes; animal faces are not detected — and Right/Left Eye Select cannot be used with Animal. The menu is documented for firmware Ver.2.00 and later; Animal detection arrived with that update, so check Setup → Version on a second-hand body.
The honest limits
There is no bird category on this body: the detection list is Human and Animal, nothing else. And with Subject Detection set to Animal, the Tracking focus area cannot be selected — for animals, work in Wide or Zone with Eye AF. Touch Tracking is the addition that works everywhere: Touch Operation On in Setup, Func. of Touch Operation set to Touch Tracking, then tap any subject on the screen to follow it, in stills and movies.
Track a person with AF-C + Tracking, flip Subject Detection to Animal for a pet, then tap-to-track with Touch Tracking — three drills, one sitting.