Live Preview Protocol

The monitoring preview is independent of the archival movie output. Negotiation prefers HEVC at 1280×720 and 30 FPS, then falls back to H.264, 960×540 or 640×360, and 20 or 15 FPS. The network preview may reduce bitrate, resolution, and frame rate; it never changes the Phase 2 archival configuration.

Preview envelopes identify codec, dimensions, timestamp, sequence, encoded payload, and keyframe state. Video messages are bounded to two megabytes. The iPad renders a native SwiftUI-compatible monitoring surface. The validated simulator source generates deterministic ordered frames; physical VideoToolbox latency and pixel output remain device-validation items.

Adaptation reacts to latency, observable loss, decoder queue depth, thermal constraint, and encoder pressure. It degrades immediately in bounded steps but requires five healthy observations before improving, avoiding rapid oscillation. Telemetry reports preview FPS, dropped preview frames, latency, and quality separately from archival FPS and drops.