“In his epochal review of Beethoven’s Symphony No. 5 in C minor (1808), Op. 67, E. T. A. Hoffman praised it as ‘one of the most important works of the time.’ … Beethoven started to sketch the Fifth Symphony in 1804, almost immediately following the completion of Symphony No. 3, Eroica … During the long four-year period of composition, Beethoven broke convention on several aspects,” (esm.rochester.edu). “Most particularly, it was the first symphony that Beethoven wrote in a minor key—C minor. Minor-keyed symphonies were not unheard of, but were not the norm at the time.”
The second movement begins with a lighter mood than its infamous introduction, the symphony’s first movement: ” … (it) begins piano with a noble, restrained theme in A-flat in the lower strings before bursting into a brief forte contrasting C-major militaristic theme, featuring trumpets and timpani.” In this performance by the Deutsche Kammerphilharmonie Bremen, this modulation occurs at 1:17; other shifts in tonality follow.