Hands-free rewind: raise your hand to go back

[nathanael]

Why

When you're mid-presentation and stumble over a line, your hands are often gesturing or holding notes — you can't easily reach the keyboard to rewind. This feature lets you raise your hand to pause and automatically rewind the teleprompter, then lower it to resume exactly where you left off. No keyboard, no mouse, no breaking your flow.

What it does

• Raise hand → teleprompter pauses and starts rewinding through words
• Hand height controls speed — higher hand = faster rewind
• Lower hand → speech recognition resumes from the new position
• Visual indicator — spinning circle in the corner shows rewind is active
• Uses Vision framework for real-time hand pose detection via built-in camera
• Hysteresis prevents jittery toggling near the detection threshold

How it works

• HandGestureController captures camera frames and runs VNDetectHumanHandPoseRequest
• Tracks wrist Y position with a smoothing window for stable detection
• SpeechRecognizer gains pauseForRewind(), rewindByWords(), and resumeAfterRewind()
• Rewind speed scales with hand height (1/2/4 words per tick)
• Camera session properly cleaned up on stop to prevent resource leaks

Test plan

• Start teleprompter in word tracking mode, raise hand — verify pause + rewind
• Vary hand height — verify rewind speed changes
• Lower hand — verify speech recognition resumes
• Verify spinning indicator appears/disappears correctly
• Test with different lighting conditions
• Verify camera permission prompt appears on first use