Lock video focus once instead of hunting continuously

[spollard]

Problem

The video recording pipelines in Camera.qml build a droidcamsrc element but never set its focus-mode. It therefore falls back to the GstPhotography default CONTINUOUS_NORMAL, which on the Android camera HAL re-runs autofocus for the entire recording. The lens visibly hunts in and out, degrading every video.

Fix

Set focus-mode=auto (single-shot autofocus, then hold) on droidcamsrc in both the front and back record pipelines, so the camera focuses once at the start of recording and then keeps that focus steady. Two-line change, no behavioural change to stills or the viewfinder.

Measurements (FuriPhone radon)

Recorded the same scene through the existing back-record pipeline with the only difference being focus-mode, then computed a per-frame sharpness metric (Brenner gradient):

droidcamsrc focus-mode	post-1s sharpness jitter	behaviour
continuous-normal (current default)	0.56	sharpness bounces, lens hunting
auto (this PR)	0.02	focuses once, holds steady

auto also has a higher mean sharpness, since the image no longer repeatedly racks through blur.

If a fully fixed lens is ever preferred (e.g. for landscapes), focus-mode=infinity/manual are the alternatives — but auto keeps a sharp starting focus, which is the better general-purpose default.

🤖 Generated with Claude Code