Call it an end-of-year resolution for higher resolution: Amazon says its long-promised 4K video streaming service will arrive before the end of the year.

Amazon, along with a few other companies, promised it would offer the next-generation video for compatible Ultra HD TVs back at CES in January. But even as Ultra HD TV prices have dropped to as low as $1,000, streaming 4K content has been hard to come by. Netflix was the first to arrive on Ultra HD TVs in the spring, yet it now has only about a dozen movies and TV shows available...