—Ascent Media Group: Mara Sternthal has joined Ascent Media Group as SVP, business development for its Global Media Exchange (GMX) service, a video ad exchange. Sternthal will head up efforts to line up content creators and buyers. Prior to Ascent Media, she served as a consultant in the entertainment and new media space, with previous experience at studios like Paramount, Warner Bros. and Sony Pictures Entertainment.

—Brightcove: The online video platform has added Mike Quinn as SVP, sales for the Americas, from FAST Search & Transfer where he served as VP of sales. Jeff Whatcott has joined as SVP of marketing, from Acquia where he served as VP of marketing (and Adobe before it). Long-time Adobe exec David Mendels and former BrassRing CEO Deb Besemer have also joined Brightcove’s board. Release.

—Box.net: Jen Grant joins the online file sharing and storage service as its first VP of marketing, and David Lee has been named director of product management. Grant hailed from Google, where she oversaw marketing on the Apps team. Lee comes from Yahoo where he was a former video advertising product manager.

—NBCU: NBC Digital Entertainment promoted Emre Celik to VP of technology. He will oversee the technical development and support teams for NBCU’s editorial, video, mobile and social networking platforms, reporting to Stephen Andrade, NBC.com’s GM and SVP of digital development. Celik previously served as the technical director of NBC.com. 

—Birst: The on-demand business solutions platform has hired Randi Di Prima as its VP of global partners. With over 20 years of executive management experience, he has expanded global partner programs at Hyperion and Motorola (NYSE: MOT), among others.