Large performance regression fixed by moving mutex further into the Timeline::GetFrame method - only when generating a new frame (allowing cache to actually work freely). Adding mutex back to FFmpegReader::GetFrame. Removing redundant mutex from ReaderBase.h. Adding mutex to all methods that call shrink_to_fit().

src/FrameMapper.cpp

@@ -84,6 +84,9 @@ void FrameMapper::AddField(Field field)
 
 // Clear both the fields & frames lists
 void FrameMapper::Clear() {
+	// Prevent async calls to the following code
+	const std::lock_guard<std::recursive_mutex> lock(getFrameMutex);
+
     // Clear the fields & frames lists
     fields.clear();
     fields.shrink_to_fit();
@@ -104,6 +107,9 @@ void FrameMapper::Init()
 		// Skip initialization
 		return;
 
+	// Prevent async calls to the following code
+	const std::lock_guard<std::recursive_mutex> lock(getFrameMutex);
+
 	// Clear the fields & frames lists
 	Clear();