VPK file and song clipped

Sometimes a song clipped. If I remove the song in the media list and remove in the directory the VPK file, then scan again, then it is again fully played. The time information of the song in the media list is different. After it, the song time is longer and wright (time compare with mediaplayer).
My question: what kind of information is stored in a VPK file?
My question: what kind of information is stored in a VPK file?