In the movie the Bach family is portrayed having only 3 children, Friedemann, Emanuel and Friederike. In real life in the times of the movie's setting they had more children, including Catharina Dorothea, Johann Christoph Friedrich, Elisabeth Juliana Friederica, Johanna Carolna and Regina Susanna. Another son Johann Christian lived in Italy and London at the times of the movie's setting.
Friedemann Bach never wrote a ballet piece, as suggested in the movie.
In the movie Friedemann Bach dies from injuries from a fight. In real life Friedemann was sick in the last years of his life and was very little in public. It is said that he died due to tuberculosis.
Friedemann Bach was not part of a travelling theater group.
After leaving Halle Friedemann Bach is sent by his Father Johann Sebastian Bach to Dresden. However he worked in Dresden from 1733-1746, right before he gained his position as composer and organist in Halle.
Friedemann Bach left his arrangements in Halle in 1770. His father Johann Sebastian Bach died in 1750, shortly before his daughter Friederike Bach married Johann Christoph Altnikol. In the movie however he is still alive. Also his mother Anna Magdalena Bach died in 1760, 10 years before Friedemann quit his position in Halle.