codec system rework

Codecs are now much cleaner and thread safe by design.

app/codec/ffmpeg/ffmpegframepool.h

@@ -32,7 +32,7 @@ class FFmpegFramePool : public MemoryPool<uint8_t>
 public:
   FFmpegFramePool(int element_count);
 
-  void SetParameters(int width, int height, AVPixelFormat format);
+  void SetParameters(int width, int height, PixelFormat::Format format);
 
   const int& width() const
   {
@@ -52,7 +52,7 @@ private:
 
   int height_;
 
-  AVPixelFormat format_;
+  PixelFormat::Format format_;
 
 };