From fae6a60228df8cf3029982672d933dc3cc97d43c Mon Sep 17 00:00:00 2001
From: Jonathan Thomas <jonathan@openshot.org>
Date: Fri, 13 Mar 2026 23:39:22 -0500
Subject: [PATCH] Prevent Tracker crashes by resetting optical-flow state when
 the video frame size changes between tracked frames.

---
 src/CVTracker.cpp   | 18 ++++++++++++++++--
 tests/CVTracker.cpp | 37 +++++++++++++++++++++++++++++++++++++
 2 files changed, 53 insertions(+), 2 deletions(-)

diff --git a/src/CVTracker.cpp b/src/CVTracker.cpp
index f243fcfb5..b719d383e 100644
--- a/src/CVTracker.cpp
+++ b/src/CVTracker.cpp
@@ -185,11 +185,25 @@ bool CVTracker::trackFrame(cv::Mat &frame, size_t frameId)
     cv::Mat gray;
     cv::cvtColor(frame, gray, cv::COLOR_BGR2GRAY);
 
+    const bool prevGrayMatches =
+        !prevGray.empty() &&
+        prevGray.size() == gray.size() &&
+        prevGray.type() == gray.type();
+    const bool fullPrevGrayMatches =
+        !fullPrevGray.empty() &&
+        fullPrevGray.size() == gray.size() &&
+        fullPrevGray.type() == gray.type();
+
+    if (!prevGray.empty() && !prevGrayMatches) {
+        prevPts.clear();
+        lostCount = 0;
+    }
+
     cv::Rect2d cand;
     bool didKLT = false;
 
     // Try KLT-based drift
-    if (!prevGray.empty() && !prevPts.empty()) {
+    if (prevGrayMatches && !prevPts.empty()) {
         std::vector<cv::Point2f> currPts;
         std::vector<uchar> status;
         std::vector<float> err;
@@ -233,7 +247,7 @@ bool CVTracker::trackFrame(cv::Mat &frame, size_t frameId)
     if (!didKLT) {
         ++lostCount;
         cand = lastBox;
-        if (!fullPrevGray.empty()) {
+        if (fullPrevGrayMatches) {
             cv::Mat flow;
             cv::calcOpticalFlowFarneback(
                 fullPrevGray, gray, flow,
diff --git a/tests/CVTracker.cpp b/tests/CVTracker.cpp
index 0ac1116c5..9336f74eb 100644
--- a/tests/CVTracker.cpp
+++ b/tests/CVTracker.cpp
@@ -144,6 +144,43 @@ TEST_CASE( "Track_BoundingBoxClipping", "[libopenshot][opencv][tracker]" )
     CHECK(tracker_pc.GetError() == false);
 }
 
+TEST_CASE( "Track_FrameSizeChangeDoesNotCrash", "[libopenshot][opencv][tracker]" )
+{
+    std::string json_data = R"proto(
+    {
+        "tracker-type": "KCF",
+        "region": {
+            "normalized_x": 0.2,
+            "normalized_y": 0.2,
+            "normalized_width": 0.3,
+            "normalized_height": 0.3,
+            "first-frame": 1
+        }
+    } )proto";
+
+    ProcessingController tracker_pc;
+    CVTracker tracker(json_data, tracker_pc);
+
+    cv::Mat frame1(360, 640, CV_8UC3, cv::Scalar(0, 0, 0));
+    cv::rectangle(frame1, cv::Rect(128, 72, 160, 108), cv::Scalar(255, 255, 255), cv::FILLED);
+
+    cv::Mat frame2 = frame1.clone();
+
+    cv::Mat frame3(180, 320, CV_8UC3, cv::Scalar(0, 0, 0));
+    cv::rectangle(frame3, cv::Rect(64, 36, 80, 54), cv::Scalar(255, 255, 255), cv::FILLED);
+
+    REQUIRE_NOTHROW(tracker.initTracker(frame1, 1));
+    REQUIRE_NOTHROW(tracker.trackFrame(frame2, 2));
+    REQUIRE_NOTHROW(tracker.trackFrame(frame3, 3));
+
+    FrameData fd = tracker.GetTrackedData(3);
+    CHECK(fd.frame_id == 3);
+    CHECK(fd.x1 >= 0.0f);
+    CHECK(fd.y1 >= 0.0f);
+    CHECK(fd.x2 <= 1.0f);
+    CHECK(fd.y2 <= 1.0f);
+}
+
 
 TEST_CASE( "SaveLoad_Protobuf", "[libopenshot][opencv][tracker]" )
 {