From a111f214279966885d1af40766dabd0ee9867453 Mon Sep 17 00:00:00 2001
From: Scott <scott@ausocean.org>
Date: Mon, 27 Jan 2020 11:23:56 +1030
Subject: [PATCH] filter: return length from the filter's Write method

---
 filter/difference.go | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/filter/difference.go b/filter/difference.go
index 4504c6ef..d01cf0a7 100644
--- a/filter/difference.go
+++ b/filter/difference.go
@@ -76,7 +76,10 @@ func (d *Difference) Write(f []byte) (int, error) {
 	if d.prev.Empty() {
 		var err error
 		d.prev, err = gocv.IMDecode(f, gocv.IMReadColor)
-		return 0, err
+		if err != nil {
+			return 0, err
+		}
+		return len(f), nil
 	}
 
 	img, err := gocv.IMDecode(f, gocv.IMReadColor)
@@ -94,7 +97,7 @@ func (d *Difference) Write(f []byte) (int, error) {
 
 	mean := imgDelta.Mean().Val1
 
-	// Update History
+	// Update History.
 	d.prev = img.Clone()
 
 	// Draw debug information.
@@ -118,7 +121,7 @@ func (d *Difference) Write(f []byte) (int, error) {
 
 	// Don't write to destination if there is no motion.
 	if mean < d.thresh {
-		return 0, nil
+		return len(f), nil
 	}
 
 	// Write to destination.