ijksdl: YUV12 need convert U,V planar before convert
ijksdl/nativewindow: use line_height instead of minheight
ijksdl: ffmpeg-overlay: use av_frame_alloc instead of avcodec_alloc_frame();
ijksdl: use AVBufferRef to manage overlay buffer
ijkplayer: support direct draw for YUV420P and YUVJ420P