The largest U.S. bookstore chain will launch a video streaming and download service this fall for its Nook tablet and e-book reader. Barnes & Noble's (BKS) Nook has struggled to compete with Amazon.com's (AMZN) Kindle e-reader and Kindle Fire tablet, as well as Apple's (AAPL) iPad and others. The Nook video service will let shoppers buy movies and TV shows from Time Warner (TWC) HBO, Viacom (VIA), Sony (SNE) and Walt Disney Studios (DIS). Barnes & Noble shares fell 3.4% to 12.26. Amazon fell 0.9% to 252.46.