Hi, here are some elaborations :)
00:25
The long pavilion was a place for farewelling relatives and friends outside the city in ancient times. Generally, many willow trees were planted. The people who seeing people off, often folded the willows and gave them to those who are travelling far to express their thoughts (how they will miss them).
00:43
夕阳 = the setting sun, the glow of the setting sun
山外山 refers to an idiom 山外有山 人外有人, specifically the 山外有山 which means 'there are mountains outside the mountains' referring to how you may be powerful but there are others are more powerful than you. It is to persuade people not to be arrogant, but to be humble.
Though the line may also be referring to how large the world is, there are mountains beyond the mountains you know, and the glow of the sunset travels over them all. Expressing how the poet (most if not all older Chinese songs are technically poems because in ancient times, poems were sung as well as recited) wished to accompany his friends and loved ones for a longer distance as he bids farewell.
00:55
知交 is a term for 'close friend' kind of similar to 知己 (term referring to a companion that is so close that they know you better than you know yourself, closest English equivalent would be 'soulmate').
In 1927, Li Shutong's (李叔同 the writer of the lyrics; written in 1915) disciple Feng Zikai (丰子恺) personally copied the lyrics and drew illustrations, and included it in 《中文名歌五十曲》"Fifty Chinese Famous Songs", and in 1958 it was included in《李叔同歌曲集》"Li Shutong's Song Collection" .
Earliest version of lyrics:
长亭外，古道边，芳草碧连天。
晚风拂柳笛声残，夕阳山外山。
天之涯，地之角，知交半零落。
一瓢浊酒尽余欢，今宵别梦寒