Update 03/11/2015: The official site for Sound! Euphonium has now uploaded an announcement video for the new movie and TV series, which was originally screened when the two were confirmed at the KyoAni & Do Fan Days event.
This translation of the preview comes from Anime News Network‘s report:
Noboru Taki: Well then, let’s start.
Text: Special Announcement
Text: A film version that will look back at the TV series!
Noboru Taki: Now, go and show me the true strength of Kitauji.
Text: Has been decided!
Text: Road to nationals
Text on board: National competition participation
Text: Sequel work decided!
On Saturday at KyoAni & Do Fan Days, an event hosted by Kyoto Animation and Animation DO, a movie and new TV series were announced for Sound! Euphonium, the anime based on the novel by Ayano Takeda. Nikki Asada, who illustrated for Takeda, celebrated the news on Twitter with an adorable image of the main quartet together.
While Sound! Euphonium the Movie: Welcome to the Kitauji High School Concert Band will recap the events of the first series from spring 2015, the new series has been confirmed as a sequel, which will follow the events after Kitauji’s concert band compete to take part in the nationals. Aside from these precious few details, nothing else is known about the two projects for the time being, but the anime’s official website tells fans to watch this space for further announcements.