Sources confirm that Comcast, the nation’s largest cable operator with nearly 22 million video subscribers, plans to expand from renting to selling major studio movies directly through its cable boxes by the end of the year. Comcast will join streaming services such as iTunes and Vudu in offering the option to purchase titles in an evolving new window known as “early EST.” While viewers typically pay about $5 to rent a movie through VOD, digital purchases run $15-$20.

Comcast’s service will allow subscribers to purchase movies or TV episodes through their cable box or the Xfinity TV site and store the content in the cloud for viewing via television, tablet or PC.

“Major film studios see electronic sales of movies as a potentially big business that could offset the huge declines in DVD sales over the past decade,” reports The Wall Street Journal. “Currently, Verizon — which has about five million video subscribers through its FiOS service — is the only other pay TV company selling movies digitally, although Web outlets such as Apple’s iTunes and Amazon.com do so as well.”

Movies sold digitally are more profitable than rentals for the studios, but the market is relatively small. While online movie and TV show sales experienced a 49 percent year-over-year increase for the first nine months of 2013, it was only 15 percent of the $5 billion DVD sales market.

“Early EST is not to be confused with the controversial premium VOD, which involves movies bowing in tandem with or shortly after the beginning of the theatrical window,” explains Variety. “Early EST comes after hotels and airlines get films, or several weeks before the traditional three-month separation between theatrical debut and homevideo.”

Movies that have launched in the early EST window include “The Heat,” “Iron Man 3,” “The Great Gatsby” and “Star Trek Into Darkness.”

“At least initially, Comcast’s digital movie ownership service won’t be integrated with UltraViolet, an entertainment and consumer technology industries initiative to allow people to store movies or TV shows they buy from different online retailers together in the cloud,” notes WSJ. “But Comcast, which is part of the UltraViolet consortium, may integrate with it in the future, one of the knowledgeable people said.”

Comcast is reportedly in talks to include Netflix in its cable boxes and new cloud-based X1 product.