In Germany and France, the presence of a trumpeter was deemed appropiate for getting into contact with the enemy.

Here (in German) a kind of codification of the procedure and its circumstances, from 1840:

https://books.google.de/books?id=qdxKAAAAcAAJ&pg=PA296&dq=Achtes

Another German text, also from the 1840s, says a white flag is used only by besieged places:

https://books.google.de/books?id=ZtxU0-S55NsC&pg=PA259&dq=fahne