What are the markings used above some song lyrics?
The markings above the kanji are furigana, which indicate the pronunciation of the respective characters. I'm not an expert, but I recall seeing this (sometimes for all kanji, sometimes only for some) in karaoke-related videos on YouTube before. (Examples: 北酒場, for some kanji; 長崎の女, where significantly, 女 is read as ひと.) Wikipedia singles karaoke as a notable case in which furigana appears, and it makes sense that furigana may be provided for some songs even when they're not explicitly made for the purpose of karaoke (for instance, for a children's show where viewers might sing along).