Video player for QML component, using VLC as decoder.


Overview.
The pipeline of video playing is
1. the VLC parsing the input video(local file or rtsp stream),

2. decode it and output frame

3. convert them from YUV to RGB

4. upload to texture

5. displaying it.

Note:

1. main rendering thread ini VLC engine

2. load media, created media player, set callbacks

3. video format info 
    determine colorspace
    call to render thread.
    -> setupsFormat return number of plane.

4. lock callback 
    Lock Buffer Mutex(I won't mess up with the frame that displaying)
    send pixel buffer into VLC, 


5. unlock for video memory 
    -> updateTexture
    

6. display callback
   -> paintFrame.
   -> update to repaint

   QMetaObject::invokeMethod for cross thread function call.

7. when VLC thread is ready on next frame, it call lock-> unlock-> display callback in order.



Texture Mode: Synchronous Transfers
GPU -------------draw           
BUS -------upload  
CPU -- copy----------copy

PBO mode: Async transfer
save one more memory copy, vlc will draw into pixelbuffer memory space.
GPU -----------------draw0---draw1               
BUS ---------upload0-upload1-upload0  
CPU -- copy0-copy1---copy2




use shader to convert colorspace of texture?