Film fans in Germany are threatening a boycott unless cinema managers reduce the amount of adverts shown before films.It's reported cinema-goers have to sit through about 50 minutes of adverts even before trailers begin. Some audiences in Berlin were left stranded after going to see a screening of Harry Potter and the Chamber of Secrets. It had been scheduled to start at 10.15pm, but because of 45 minutes of ads, it didn't end until 1.30am by which time the city's public transport system had stopped for the night. Cinema bosses however say the commercials are necessary in order to keep...