What are the characteristics of the poems in Yuefu Poetry Collection?

Most of the poems collected in Yuefu Poetry Collection are excellent folk songs and poems created by literati because of the old topic of Yuefu. In particular, the folk songs of Han Yuefu, which are "happy because of sadness", widely and profoundly reflect the people's realistic sufferings and thoughts and feelings, such as Sang Shang, Journey to the East Gate, Fighting South of the City, Peacock Flying Southeast, etc., which have a high degree of realism, and their artistic achievements, expression techniques and language images have become the model and origin of Chinese poetry art.