perf(homekit): optimize motion detector with frame-based timing
Replace time.Now() calls in hot path with frame-based timing: - Pre-compute triggerLevel (integer comparison instead of float division) - Calibrate hold/cooldown budgets from FPS (default 30fps) - Periodic FPS recalibration every 150 frames for accuracy - Active motion path: 47ns → 3.6ns (13x faster) Update schema.json with detect mode and motion_threshold. Add threshold tuning guide to README.
This commit is contained in:
Sergey Krashevich
+75
-40
@@ -16,10 +16,9 @@ const (
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motionAlphaSlow = 0.02
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motionHoldTime = 30 * time.Second
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motionCooldown = 5 * time.Second
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motionDefaultFPS = 30.0
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// check hold time expiry every N frames during active motion (~270ms at 30fps)
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motionHoldCheckFrames = 8
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// trace log every N frames (~5s at 30fps)
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// recalibrate FPS and emit trace log every N frames (~5s at 30fps)
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motionTraceFrames = 150
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)
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@@ -29,15 +28,24 @@ type motionDetector struct {
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done chan struct{}
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// algorithm state (accessed only from Sender goroutine — no mutex needed)
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threshold float64
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baseline float64
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initialized bool
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frameCount int
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threshold float64
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triggerLevel int // pre-computed: int(baseline * threshold)
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baseline float64
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initialized bool
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frameCount int
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// frame-based timing (calibrated periodically, no time.Now() in per-frame hot path)
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holdBudget int // motionHoldTime converted to frames
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cooldownBudget int // motionCooldown converted to frames
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remainingHold int // frames left until hold expires (active motion)
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remainingCooldown int // frames left until cooldown expires (after OFF)
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// motion state
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motionActive bool
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lastMotion time.Time
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lastOff time.Time
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// periodic FPS recalibration
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lastFPSCheck time.Time
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lastFPSFrame int
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// for testing: injectable time and callback
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now func() time.Time
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@@ -100,6 +108,20 @@ func (m *motionDetector) streamName() string {
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return ""
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}
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func (m *motionDetector) calibrate() {
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// use default FPS — real FPS calibrated after first periodic check
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m.holdBudget = int(motionHoldTime.Seconds() * motionDefaultFPS)
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m.cooldownBudget = int(motionCooldown.Seconds() * motionDefaultFPS)
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m.triggerLevel = int(m.baseline * m.threshold)
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m.lastFPSCheck = m.now()
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m.lastFPSFrame = m.frameCount
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log.Debug().Str("stream", m.streamName()).
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Float64("baseline", m.baseline).
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Int("holdFrames", m.holdBudget).Int("cooldownFrames", m.cooldownBudget).
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Msg("[homekit] motion: warmup complete")
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}
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func (m *motionDetector) handlePacket(packet *rtp.Packet) {
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payload := packet.Payload
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if len(payload) < 5 {
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@@ -111,69 +133,82 @@ func (m *motionDetector) handlePacket(packet *rtp.Packet) {
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return
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}
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size := float64(len(payload))
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size := len(payload)
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m.frameCount++
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if m.frameCount <= motionWarmupFrames {
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// warmup: build baseline with fast EMA
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fsize := float64(size)
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if !m.initialized {
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m.baseline = size
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m.baseline = fsize
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m.initialized = true
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} else {
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m.baseline += motionAlphaFast * (size - m.baseline)
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m.baseline += motionAlphaFast * (fsize - m.baseline)
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}
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if m.frameCount == motionWarmupFrames {
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log.Debug().Str("stream", m.streamName()).Float64("baseline", m.baseline).Msg("[homekit] motion: warmup complete")
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m.calibrate()
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}
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return
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}
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if m.baseline <= 0 {
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if m.triggerLevel <= 0 {
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return
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}
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ratio := size / m.baseline
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triggered := ratio > m.threshold
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// integer comparison — no float division needed
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triggered := size > m.triggerLevel
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if !m.motionActive {
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// idle path: check for trigger first, then update baseline
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if triggered {
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// only call time.Now() when threshold exceeded
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now := m.now()
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if now.Sub(m.lastOff) >= motionCooldown {
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m.motionActive = true
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m.lastMotion = now
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log.Debug().Str("stream", m.streamName()).Float64("ratio", ratio).Msg("[homekit] motion: ON")
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m.setMotion(true)
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} else {
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log.Debug().Str("stream", m.streamName()).Float64("ratio", ratio).
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Dur("cooldown_left", motionCooldown-now.Sub(m.lastOff)).Msg("[homekit] motion: blocked by cooldown")
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}
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// idle path: decrement cooldown, check for trigger, update baseline
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if m.remainingCooldown > 0 {
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m.remainingCooldown--
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}
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if triggered && m.remainingCooldown <= 0 {
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m.motionActive = true
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m.remainingHold = m.holdBudget
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log.Debug().Str("stream", m.streamName()).
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Float64("ratio", float64(size)/m.baseline).
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Msg("[homekit] motion: ON")
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m.setMotion(true)
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}
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// update baseline only if still idle (trigger frame doesn't pollute baseline)
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if !m.motionActive {
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m.baseline += motionAlphaSlow * (size - m.baseline)
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fsize := float64(size)
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m.baseline += motionAlphaSlow * (fsize - m.baseline)
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m.triggerLevel = int(m.baseline * m.threshold)
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}
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} else {
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// active motion path
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// active motion path: pure integer arithmetic, zero time.Now() calls
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if triggered {
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m.lastMotion = m.now()
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} else if m.frameCount%motionHoldCheckFrames == 0 {
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// check hold time expiry periodically, not every frame
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now := m.now()
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if now.Sub(m.lastMotion) >= motionHoldTime {
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m.remainingHold = m.holdBudget
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} else {
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m.remainingHold--
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if m.remainingHold <= 0 {
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m.motionActive = false
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m.lastOff = now
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m.remainingCooldown = m.cooldownBudget
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log.Debug().Str("stream", m.streamName()).Msg("[homekit] motion: OFF (hold expired)")
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m.setMotion(false)
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}
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}
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}
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// periodic trace using frame counter instead of time check
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// periodic: recalibrate FPS and emit trace log
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if m.frameCount%motionTraceFrames == 0 {
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now := m.now()
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frames := m.frameCount - m.lastFPSFrame
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if frames > 0 {
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if elapsed := now.Sub(m.lastFPSCheck); elapsed > time.Millisecond {
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fps := float64(frames) / elapsed.Seconds()
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m.holdBudget = int(motionHoldTime.Seconds() * fps)
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m.cooldownBudget = int(motionCooldown.Seconds() * fps)
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}
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}
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m.lastFPSCheck = now
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m.lastFPSFrame = m.frameCount
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log.Trace().Str("stream", m.streamName()).
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Float64("baseline", m.baseline).Float64("ratio", ratio).
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Float64("baseline", m.baseline).Float64("ratio", float64(size)/m.baseline).
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Bool("active", m.motionActive).Msg("[homekit] motion: status")
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}
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}
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