Apple TV is in talks to start carrying Time Warner's HBO Go application on their set-top boxes, possibly by the middle of 2013, according to two unidentified sources. If a deal is finalized, HBO subscribers will be able to watch over 600 hours of programming on their Apple TV devices.

Adding HBO Go would provide a sizable boost to Apple TV's lineup of services, which already include Netflix and Hulu Plus. The service is already facing serious competition from similar devices such as Roku and Microsoft's XBox. There are currently HBO Go applications available for the iPhone and iPad.

RELATED: You Season 3 Will Begin Filming This Autumn for Netflix

Here's what Apple CEO Tim Cook had to say, when asked about the prospect of HBO Go on a conference call earlier this month.

"This is an area of intense interest for us. I tend to believe that there's a lot we can contribute in this space. And so we continue to pull the string and see where it leads us."

Apple has sold approximately 2.3 million Apple TV units in the first quarter of their fiscal year, which ended in December 2012. Over the past two fiscal years combined, the company has moved over 7 million Apple TV units.