Flag process_real_time threw error with webcam

doc/release_notes.md

@@ -41,3 +41,5 @@ OpenPose Library - Release Notes
 3. Main bugs fixed:
     1. All visualization functions moved to same thread, so it works with most OpenCV custom compiled versions.
     2. Fixed error on debug mode: `Too many resources requested for launch`.
+    3. Bug in Array::getConstCvMat() if mVolume=0, now returning empty cv::Mat.
+    4. Bug: `--process_real_time` threw error with webcam.

src/openpose/producer/producer.cpp

@@ -67,10 +67,16 @@ namespace op
         try
         {
             check(fpsMode == ProducerFpsMode::RetrievalFps || fpsMode == ProducerFpsMode::OriginalFps, "Unknown ProducerFpsMode.", __LINE__, __FUNCTION__, __FILE__);
-            check(fpsMode != ProducerFpsMode::OriginalFps || get(CV_CAP_PROP_FPS) > 0,
-                  "Selected to keep the source fps but get(CV_CAP_PROP_FPS) <= 0, i.e. the source did not set its fps property.", __LINE__, __FUNCTION__, __FILE__);
-
-            mProducerFpsMode = {fpsMode};
+            // For webcam, ProducerFpsMode::OriginalFps == ProducerFpsMode::RetrievalFps, since the internal webcam cache will overwrite frames after it gets full
+            if (mType == ProducerType::Webcam)
+                mProducerFpsMode = {ProducerFpsMode::RetrievalFps};
+            // If no webcam
+            else
+            {
+                check(fpsMode == ProducerFpsMode::RetrievalFps || get(CV_CAP_PROP_FPS) > 0,
+                      "Selected to keep the source fps but get(CV_CAP_PROP_FPS) <= 0, i.e. the source did not set its fps property.", __LINE__, __FUNCTION__, __FILE__);
+                mProducerFpsMode = {fpsMode};
+            }
             reset(mNumberEmptyFrames, mTrackingFps);
         }
         catch (const std::exception& e)