[keyframe] Handle missing frames within an input video

If a frame is missing in a video sequence, instead of throwing an exception
straight away, try reading the next frame. If the next frame is valid, then
push dummy scores for the missing frame, and keep processing the input
video. Otherwise, do throw the exception and stop the process.

src/aliceVision/keyframe/KeyframeSelector.cpp

@@ -341,7 +341,33 @@ bool KeyframeSelector::computeScores(const std::size_t rescaledWidthSharpness, c
                 feed.goToNextFrame();
             }
 
-            currentMatSharpness = readImage(feed, rescaledWidthSharpness);  // Read image for sharpness and rescale it if requested
+            /* Handle input feeds that may have invalid or missing frames:
+             *   - catch the "invalid argument" exception thrown by "readImage" if a frame is invalid or missing
+             *   - try reading the next frame instead
+             *   - if the next frame is correctly read, then push dummy scores for the invalid frame and go on with
+             *     the process
+             *   - otherwise (feed not correctly moved to the next frame), throw a runtime error exception as something
+             *     is wrong with the video
+             */
+            try {
+                currentMatSharpness = readImage(feed, rescaledWidthSharpness);  // Read image for sharpness and rescale it if requested
+            } catch (const std::invalid_argument& ex) {
+                // currentFrame + 1 = currently evaluated frame with indexing starting at 1, for display reasons
+                // currentFrame + 2 = next frame to evaluate with indexing starting at 1, for display reasons
+                ALICEVISION_LOG_WARNING("Invalid or missing frame " << currentFrame + 1
+                                        << ", attempting to read frame " << currentFrame + 2 << ".");
+                bool success = feed.goToFrame(++currentFrame);
+                if (success) {
+                    // Will throw an exception if next frame is also invalid
+                    currentMatSharpness = readImage(feed, rescaledWidthSharpness);
+                    // If no exception has been thrown, push dummy scores for the frame that was skipped
+                    _sharpnessScores.push_back(-1.f);
+                    _flowScores.push_back(-1.f);
+                } else
+                    ALICEVISION_THROW_ERROR("Could not go to frame " << currentFrame + 1
+                                            << " either. The feed might be corrupted.");
+            }
+
             if (rescaledWidthSharpness == rescaledWidthFlow) {
                 currentMatFlow = currentMatSharpness;
             } else {
@@ -570,7 +596,19 @@ bool KeyframeSelector::exportFlowVisualisation(const std::size_t rescaledWidth)
                 feed.goToNextFrame();
             }
 
-            currentMat = readImage(feed, rescaledWidth);  // Read image and rescale it if requested
+            // Handle invalid or missing frames
+            try {
+                currentMat = readImage(feed, rescaledWidth);  // Read image and rescale it if requested
+            } catch (const std::invalid_argument& ex) {
+                ALICEVISION_LOG_WARNING("Invalid or missing frame " << currentFrame + 1
+                                        << ", attempting to read frame " << currentFrame + 2 << ".");
+                bool success = feed.goToFrame(++currentFrame);
+                if (success)
+                    currentMat = readImage(feed, rescaledWidth);
+                else
+                    ALICEVISION_THROW_ERROR("Could not go to frame " << currentFrame + 1
+                                            << " either. The feed might be corrupted.");
+            }
 
             if (currentFrame > 0) {
                 cv::Mat flow;