Improvement to video caching thread, to recover from the separation o…

…f cache vs display frame #. Also found a mutex that was needed, to prevent crashing when the video thread calls timeline::GetFrame at certain times... colliding with another thread (and independent of OpenMP).

src/Qt/VideoCacheThread.cpp

@@ -94,8 +94,10 @@ namespace openshot
 		while (!threadShouldExit() && is_playing) {
 
 	    // Cache frames before the other threads need them
-	    // Cache frames up to the max frames
-	    while (speed == 1 && (position - current_display_frame) < max_frames)
+	    // Cache frames up to the max frames. Reset to current position
+		// if cache gets too far away from display frame. Cache frames
+		// even when player is paused (i.e. speed 0).
+	    while ((position - current_display_frame) < max_frames)
 	    {
 	    	// Only cache up till the max_frames amount... then sleep
 			try
@@ -104,6 +106,14 @@ namespace openshot
 					ZmqLogger::Instance()->AppendDebugMethod("VideoCacheThread::run (cache frame)", "position", position, "current_display_frame", current_display_frame, "max_frames", max_frames, "needed_frames", (position - current_display_frame));
 
 					// Force the frame to be generated
+					if (reader->GetCache()->GetSmallestFrame()) {
+						int64_t smallest_cached_frame = reader->GetCache()->GetSmallestFrame()->number;
+						if (smallest_cached_frame > current_display_frame) {
+							// Cache position has gotten too far away from current display frame.
+							// Reset the position to the current display frame.
+							position = current_display_frame;
+						}
+					}
 					reader->GetFrame(position);
 				}
 
@@ -113,14 +123,8 @@ namespace openshot
 				// Ignore out of bounds frame exceptions
 			}
 
-			// Is cache position behind current display frame?
-			if (position < current_display_frame) {
-				// Jump ahead
-				position = current_display_frame;
-			}
-
 	    	// Increment frame number
-	    	position++;
+			position++;
 	    }
 
 		// Sleep for 1 frame length

src/Qt/VideoCacheThread.h

@@ -45,10 +45,13 @@ namespace openshot
      */
     class VideoCacheThread : Thread
     {
+	private:
+	std::atomic_int position;
+
+	protected:
 	std::shared_ptr<Frame> frame;
 	int speed;
 	bool is_playing;
-	int64_t position;
 	int64_t current_display_frame;
 	ReaderBase *reader;
 	int max_frames;

src/Timeline.cpp

@@ -695,6 +695,7 @@ std::shared_ptr<Frame> Timeline::GetFrame(int64_t requested_frame)
 
 	// Check cache
 	std::shared_ptr<Frame> frame;
+	std::lock_guard<std::mutex> guard(get_frame_mutex);
 	#pragma omp critical (T_GetFrame)
 	frame = final_cache->GetFrame(requested_frame);
 	if (frame) {
@@ -724,6 +725,15 @@ std::shared_ptr<Frame> Timeline::GetFrame(int64_t requested_frame)
 			return frame;
 		}
 
+		// Check if previous frame was cached? (if not, assume we are seeking somewhere else on the Timeline, and need
+		// to clear all cache (for continuity sake). For example, jumping back to a previous spot can cause issues with audio
+		// data where the new jump location doesn't match up with the previously cached audio data.
+		std::shared_ptr<Frame> previous_frame = final_cache->GetFrame(requested_frame - 1);
+		if (!previous_frame) {
+			// Seeking to new place on timeline (destroy cache)
+			ClearAllCache();
+		}
+
 		// Minimum number of frames to process (for performance reasons)
 		int minimum_frames = OPEN_MP_NUM_PROCESSORS;
 

src/Timeline.h

@@ -33,6 +33,7 @@
 
 #include <list>
 #include <memory>
+#include <mutex>
 #include <set>
 #include <QtGui/QImage>
 #include <QtGui/QPainter>
@@ -175,6 +176,7 @@ namespace openshot {
 		std::set<openshot::FrameMapper*> allocated_frame_mappers; ///< all the frame mappers we allocated and must free
 		bool managed_cache; ///< Does this timeline instance manage the cache object
 		std::string path; ///< Optional path of loaded UTF-8 OpenShot JSON project file
+		std::mutex get_frame_mutex; ///< Mutex to protect GetFrame method from different threads calling it
 
 		/// Process a new layer of video or audio
 		void add_layer(std::shared_ptr<openshot::Frame> new_frame, openshot::Clip* source_clip, int64_t clip_frame_number, int64_t timeline_frame_number, bool is_top_clip, float max_volume);