A capability stays maintainable only when the team can explain every state, retry, and piece of residual data—not merely show one successful run. Screen pixels are opaque to screen readers and system audio has no captions. Let sharers provide a title and description and connect audio to caption tracks.
Accessibility is not a late set of ARIA attributes. Keyboard, screen-reader, zoom, reduced-motion, and high-contrast users need the same complete task and a discoverable next step after errors.
Questions the design must answer
List non-negotiable invariants before selecting performance knobs. Tuning can roll out gradually; identity, permission, and terminal-state rules cannot drift at runtime.
- Label viewer video, make controls keyboard-operable, allow caption sizing and position, describe key visuals, and offer accessible source files.
- Give state one owner, a version, and terminal states; callbacks may mutate only the version that created them.
- Use explicit capability negotiation so older clients receive an explained fallback instead of a half-working state.
The delivery standard for Accessible Screen Sharing with Captions and Keyboard Controls is a usable normal path, convergent failures, bounded resources, and a state users can understand. The result is a production capability that can be explained, degraded safely, and rolled back—not a demo that works once.
Edge cases are part of the feature
An abnormal path is more than an error banner. It decides how in-flight work stops, how the peer learns the outcome, what residue remains, and whether the next operation inherits it.
- Unlabeled automatic captions can mislead, while fullscreen controls outside focus order trap keyboard users.
- A stale response arriving after a new task can overwrite healthy state or restart cancelled work without version fencing.
- Ideal-size tests miss large files, long sessions, and concurrency that cross hidden limits and cause cascading failure.
Prove that it works with evidence
Do not stop verification when the final action succeeds. Count side effects, measure wait time, inspect privacy, and prove the next run begins from a clean baseline.
- With keyboard and screen reader, enter fullscreen, toggle and resize captions, leave sharing, and get an alternative file, including after refresh.
- Run one hundred start, fail, retry, and cancel cycles; handles, listeners, queues, and temporary data must return to baseline.
- Use fault injection to prove alerts precede user reports and operators can locate the failing phase from bounded evidence.
The release bar is clear: users understand the current state, failures stop or recover, resources stay bounded, and operators can identify the phase from minimum necessary evidence.