Starz STRZA +7.08% extended its agreement with Sony Corp.’s 6758.TO -10.14% film business by five years, giving the premium cable network exclusive pay-television rights to Sony Pictures Entertainment movie releases through 2021.

Class A shares were up 8% at $18 in midday trading.

The deal comes about two months after Starz was outbid by Netflix Inc. NFLX -1.76% for rights to Walt Disney Co. DIS +0.16% movies.

The new agreement with Sony provides movie content for all Starz platforms including its Starz and Encore channels as well as through on-demand and online streaming services.

Financial terms of the deal weren’t disclosed.

Starz was spun off by Liberty Media Corp. LMCA +0.78% in January as Liberty aimed to free up cash to pursue its effort to take over Sirius XM Radio Inc. SIRI +0.96%

The developments at Starz reflect broader shifts in the premium cable sector, long dominated by Time Warner Inc.’s TWX -1.09% HBO and CBS Corp.’s CBS -1.26% Showtime. While these channels originated as outlets for movies, the proliferation of movies on various outlets including on-demand services and cheap DVD rental services has reduced their value for premium movie channels.