This concerto was scored for solo violin, two solo recorders, basso continuo, viola, cello, violone and two violins, and it lasts around 16 minutes. The violin part in this concerto is extremely virtuosic in the first and third movements. In the second movement, the violin provides a bass when the concertino group plays unaccompanied.

Reference : https://musopen.org/music/1218/johann-sebastian-bach/brandenburg-concerto-no4-in-g-major-bwv-1049/