Streaming media player Roku is now offering demographic guarantees for TV marketers that use its advertising platform, in hopes of unifying the TV and OTT advertising landscapes. Roku claims it’s the first OTT advertising publisher to offer advertising metrics through Nielsen’s Digital Ad Ratings (DAR) that are comparable to linear TV, calling it a major milestone marker for the industry. “Consumers are migrating their TV viewing to OTT platforms like Roku, making them increasingly difficult to reach through traditional TV advertising,” said Scott Rosenberg SVP of advertising at Roku. “As TV buyers follow this migration, they need a common currency to plan their investment mix across linear and OTT.” Roku partnered with Nielsen back in 2015 to integrate its DAR…