int mp4_open_meta(const struct mp4_callback *cb, struct mp4 **result);
struct mp4_metadata *mp4_get_meta(struct mp4 *f);
int mp4_meta_update(struct mp4 *f);
-char *mp4_meta_get_artist(const struct mp4 *f);
-char *mp4_meta_get_title(const struct mp4 *f);
-char *mp4_meta_get_date(const struct mp4 *f);
-char *mp4_meta_get_album(const struct mp4 *f);
-char *mp4_meta_get_comment(const struct mp4 *f);
+char *mp4_get_tag_value(const struct mp4 *f, const char *item);