Passengers on the line, which runs from downtown to Old Town, then east through Mission Valley to El Cajon and Santee, can watch movies, television shows, cartoons, action sports, Hollywood updates and other entertainment for free, according to the MTS.
The MTS-TV service is available for smartphones, laptops and tablets.
"This first-of-its-kind offering is meant to enhance the experience of our trolley passengers who rely on us daily to get to their destinations,'' said Paul Jablonski, CEO of the agency. "Public transportation plays a vital role in the San Diego region and our goal is to offer new features as services grow.''
Passengers can access video programming by connecting to the MTS-TV WiFi on their mobile device or opening the MTS-TV home page on their Internet browser.
Riders on the Blue and Orange lines will be able to use MTS-TV by the end of the month.
According to the MTS, the service will be available at major stations on all three lines by the end of September.
FlashPoints Media Group created MTS-TV and will share advertising revenue with the agency. Cox Communications is also participating by providing "Sam the Cooking Guy'' programming.
Viewers can also select from movies in English and Spanish, movie trailers, "About San Diego: Destinations and Sights'' and productions from the San Diego Zoo, among other offerings.