fix a number of memory leaks

- some were with libav functions
- same were due to non-virtual destructors

src/CacheBase.cpp

@@ -42,6 +42,9 @@ CacheBase::CacheBase(int64_t max_bytes) : max_bytes(max_bytes) {
 	cacheCriticalSection = new CriticalSection();
 };
 
+CacheBase::~CacheBase() {
+};
+
 // Set maximum bytes to a different amount based on a ReaderInfo struct
 void CacheBase::SetMaxBytesFromInfo(int64_t number_of_frames, int width, int height, int sample_rate, int channels)
 {
@@ -69,4 +72,4 @@ void CacheBase::SetJsonValue(Json::Value root) {
 	// Set data from Json (if key is found)
 	if (!root["max_bytes"].isNull())
 		max_bytes = atoll(root["max_bytes"].asString().c_str());
-}
+}