Amazon.com has approached big entertainment companies about licensing their television channels for a new online pay-TV service it is considering launching, in what would mark a significant expansion of the company’s online video efforts. The new service under consideration would offer live TV channels, such as those available now on cable or satellite TV. Through its Prime Instant Video service, Amazon now offers various TV shows and movies on demand for subscribers to its Prime free-shipping service. Still, Amazon’s initiative is in the early stages, and it isn’t clear whether it will move forward. Several other tech companies including Sony and Google are pursuing similar initiatives. An Amazon spokesman declined to comment. Amazon is also developing a set-top box to stream video, much like a Roku player, The Wall Street Journal previously reported.