[keyframe] Handle corner case when identifying subsequences

This commit handles the specific case where the last frame of an input
sequence happens to be the one that pushes the motion accumulation over
the threshold: the last frame was being pushed a first time within the
'for' loop, and then a second time outside of it. This led the last
subsequence to have a size of 0, which led to the 'while' loop condition
filling the weights' vector to never be broken.

src/aliceVision/keyframe/KeyframeSelector.cpp

@@ -217,7 +217,10 @@ void KeyframeSelector::processSmart(const float pxDisplacement, const std::size_
 
     float step = pxDisplacement * std::min(_frameWidth, _frameHeight) / 100.0;
     double motionAcc = 0.0;
-    for (std::size_t i = 1; i < sequenceSize; i++) {  // Starts at 1 because the first frame's motion score will be -1
+
+    /* Starts at 1 because the first frame's motion score will be -1.
+     * Ends at sequenceSize - 1 to ensure the last frame cannot be pushed twice. */
+    for (std::size_t i = 1; i < sequenceSize -1; i++) {
         motionAcc += _flowScores.at(i);
         if (motionAcc >= step) {
             subsequenceLimits.push_back(i);
@@ -248,7 +251,7 @@ void KeyframeSelector::processSmart(const float pxDisplacement, const std::size_
                 }
                 motionAcc = 0.0;
 
-                for (std::size_t i = 1; i < sequenceSize; i++) {
+                for (std::size_t i = 1; i < sequenceSize - 1; i++) {
                     motionAcc += _flowScores.at(i);
                     if (motionAcc >= step) {
                         newLimits.push_back(i);
@@ -264,7 +267,7 @@ void KeyframeSelector::processSmart(const float pxDisplacement, const std::size_
                 newLimits.push_back(0);
                 std::size_t stepSize = (sequenceSize / _minOutFrames) + 1;
 
-                for (std::size_t i = 1; i < sequenceSize; i += stepSize)
+                for (std::size_t i = 1; i < sequenceSize - 1; i += stepSize)
                     newLimits.push_back(i);
                 newLimits.push_back(sequenceSize - 1);
             }
@@ -276,7 +279,7 @@ void KeyframeSelector::processSmart(const float pxDisplacement, const std::size_
                 step = step + displacementDiff;
                 motionAcc = 0.0;
 
-                for (std::size_t i = 1; i < sequenceSize; i++) {
+                for (std::size_t i = 1; i < sequenceSize - 1; i++) {
                     motionAcc += _flowScores.at(i);
                     if (motionAcc >= step) {
                         newLimits.push_back(i);
@@ -296,6 +299,7 @@ void KeyframeSelector::processSmart(const float pxDisplacement, const std::size_
         double bestSharpness = 0.0;
         std::size_t bestIndex = 0;
         std::size_t subsequenceSize = subsequenceLimits.at(i) - subsequenceLimits.at(i - 1);
+        ALICEVISION_LOG_DEBUG("Subsequence [" << subsequenceLimits.at(i - 1) << ", " << subsequenceLimits.at(i) << "]");
 
         // Weights for the whole subsequence [1.0; 2.0] (1.0 is on the subsequence's limits, 2.0 on its center)
         std::deque<double> weights;
@@ -320,10 +324,12 @@ void KeyframeSelector::processSmart(const float pxDisplacement, const std::size_
                 bestSharpness = sharpness;
             }
         }
-        ALICEVISION_LOG_DEBUG("Selecting frame " << bestIndex);
+        ALICEVISION_LOG_DEBUG("Selecting frame with ID " << bestIndex);
         _selectedKeyframes.push_back(bestIndex);
         _selectedFrames.at(bestIndex) = '1';  // The frame has been selected, flip it to 1
     }
+
+    ALICEVISION_LOG_DEBUG("Finished selecting all the keyframes!");
 }
 
 bool KeyframeSelector::computeScores(const std::size_t rescaledWidth, const std::size_t sharpnessWindowSize,