const std::set<Track *> &get_tracks() const { return tracks; }
void add_track(Track &);
void remove_track(Track &);
void check_links();
void load(const std::string &);
int save(const std::string &);
const std::set<Track *> &get_tracks() const { return tracks; }
void add_track(Track &);
void remove_track(Track &);
void check_links();
void load(const std::string &);
int save(const std::string &);