Position is changing when song is playing. Seek function will also change position, even if song isn't playing. 

If you seek position and song isn't playing, retrieved position will be also changed to seek position. 

To get current position use:  

ZPlay C++ Class interface

• GetPosition

C Style interface

• zplay_GetPosition

On streams with variable bitrate, bitrate is changing in time. 

You can retrieve current bitrate with:  

Stream informations