From 207e96b9999f213e6e657993752b4774b72f3996 Mon Sep 17 00:00:00 2001
From: Scott <scott@ausocean.org>
Date: Thu, 23 Jan 2020 12:43:09 +1030
Subject: [PATCH] KNN filter detects motion on an interval

---
 filter/knn.go  | 37 +++++++++++++++++++++++++++----------
 revid/revid.go |  2 +-
 2 files changed, 28 insertions(+), 11 deletions(-)

diff --git a/filter/knn.go b/filter/knn.go
index be733ec0..cc5a8a37 100644
--- a/filter/knn.go
+++ b/filter/knn.go
@@ -40,23 +40,26 @@ import (
 // KNNFilter is a filter that provides basic motion detection. KNN is short for
 // K-Nearest Neighbours method.
 type KNNFilter struct {
-	dst     io.WriteCloser
-	area    float64
-	bs      *gocv.BackgroundSubtractorKNN
-	knl     gocv.Mat
-	debug   bool
-	windows []*gocv.Window
+	dst     io.WriteCloser                // Destination to which motion containing frames go.
+	area    float64                       // The minimum area that a contour can be found in.
+	bs      *gocv.BackgroundSubtractorKNN // Uses the KNN algorithm to find the difference between the current and background frame.
+	knl     gocv.Mat                      // Matrix that is used for calculations.
+	debug   bool                          // If true then debug windows with the bounding boxes and difference will be shown on the screen.
+	windows []*gocv.Window                // Holds debug windows.
+	hold    [][]byte                      // Will hold all frames up to hf (so only every hf frame is motion detected).
+	hf      int                           // The number of frames to be held.
+	hfCount int                           // Counter for the hold array.
 }
 
 // NewKNNFilter returns a pointer to a new KNNFilter.
-func NewKNNFilter(dst io.WriteCloser, area, threshold float64, history, kernelSize int, debug bool) *KNNFilter {
+func NewKNNFilter(dst io.WriteCloser, area, threshold float64, history, kernelSize int, debug bool, hf int) *KNNFilter {
 	bs := gocv.NewBackgroundSubtractorKNNWithParams(history, threshold, false)
 	k := gocv.GetStructuringElement(gocv.MorphRect, image.Pt(kernelSize, kernelSize))
 	var windows []*gocv.Window
 	if debug {
 		windows = []*gocv.Window{gocv.NewWindow("KNN: Bounding boxes"), gocv.NewWindow("KNN: Motion")}
 	}
-	return &KNNFilter{dst, area, &bs, k, debug, windows}
+	return &KNNFilter{dst, area, &bs, k, debug, windows, make([][]byte, hf-1), hf, 0}
 }
 
 // Implements io.Closer.
@@ -75,6 +78,13 @@ func (m *KNNFilter) Close() error {
 // Write applies the motion filter to the video stream. Only frames with motion
 // are written to the destination encoder, frames without are discarded.
 func (m *KNNFilter) Write(f []byte) (int, error) {
+	if m.hfCount < (m.hf - 1) {
+		m.hold[m.hfCount] = f
+		m.hfCount++
+		return len(f), nil
+	}
+	m.hfCount = 0
+
 	img, err := gocv.IMDecode(f, gocv.IMReadColor)
 	if err != nil {
 		return 0, fmt.Errorf("can't decode image: %w", err)
@@ -125,9 +135,16 @@ func (m *KNNFilter) Write(f []byte) (int, error) {
 
 	// Don't write to destination if there is no motion.
 	if len(contours) == 0 {
-		return -1, nil
+		return len(f), nil
 	}
 
-	// Write to destination.
+	// Write to destination, past 4 frames then current frame.
+	for i, h := range m.hold {
+		_, err := m.dst.Write(h)
+		m.hold[i] = nil
+		if err != nil {
+			return len(f), fmt.Errorf("could not write previous frames: %w", err)
+		}
+	}
 	return m.dst.Write(f)
 }
diff --git a/revid/revid.go b/revid/revid.go
index b4b83892..3ab6c704 100644
--- a/revid/revid.go
+++ b/revid/revid.go
@@ -341,7 +341,7 @@ func (r *Revid) setupPipeline(mtsEnc func(dst io.WriteCloser, rate float64) (io.
 			case config.FilterVariableFPS:
 				r.filters[i] = filter.NewVariableFPSFilter(dst, r.cfg.MinFPS, filter.NewMOGFilter(dst, r.cfg.MOGMinArea, r.cfg.MOGThreshold, int(r.cfg.MOGHistory), r.cfg.ShowWindows, r.cfg.MotionInterval))
 			case config.FilterKNN:
-				r.filters[i] = filter.NewKNNFilter(dst, r.cfg.KNNMinArea, r.cfg.KNNThreshold, int(r.cfg.KNNHistory), int(r.cfg.KNNKernel), r.cfg.ShowWindows)
+				r.filters[i] = filter.NewKNNFilter(dst, r.cfg.KNNMinArea, r.cfg.KNNThreshold, int(r.cfg.KNNHistory), int(r.cfg.KNNKernel), r.cfg.ShowWindows, r.cfg.MotionInterval)
 			default:
 				panic("Undefined Filter")
 			}