Performance Logging (Developer settings) logs a resource sample every 5s
in the foreground and background: CPU by area and thread, wakeups, GPU,
memory, disk, activity counters as rates (mpv property updates, player
time publishes, renders, saves, network, images, CloudKit events, log
entries, main run-loop wakeups), SwiftUI body evaluations of the player
views, and app/player/battery context. Each foreground/background
transition logs a summary of the period. MetricKit metrics and
diagnostics (CPU exceptions, hangs) are logged whenever logging is on.
Background diagnostics (iOS) log lifecycle, audio session and power
events with an app/player/render snapshot and a heartbeat that detects
suspension gaps and main-thread stalls. Logs are persisted per session
in Caches/Logs and the previous session is included in exports, so logs
survive the app being swiped away.
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