What are the good video platforms for synchronous tutoring in junior high school mathematics?

At present, the Sanhao open class platform covers all the videos of junior high school courses. The course covers the knowledge points of junior high school mathematics courses in all grades. The course content is arranged reasonably, taking into account the differences of teaching materials and examinations in different places, and covering all knowledge points. Teachers are screened at different levels, and front-line teachers are adopted. They have rich teaching experience, and they can watch the playback time after class to study repeatedly, which is of great help to junior high school mathematics learning.