Sezmi, a start-formerly known as Building B, plans to change the way we watch TV through a combination of broadband and over-the-air television.

The Belmont, Calif., company promises to give consumers a new option for pay TV and an easy way to watch movies, TV, and Internet video all in one convenient place, where switching between video sources is as easy as changing channels.

Before the end of the year, Sezmi will sell a set-top box that will deliver live TV via local TV stations, pre-recorded and archived shows, and video from the Internet. The proprietary set-top will launch with DSL and 3G service provider options.

The company’s main innovation is a FlexCast video distribution technology that combines terrestrial digital TV broadcasts with broadband to deliver its programs to a set-top box. It uses that combination to create a private and secure connection to the user’s set-top so that can deliver personalized programming on existing infrastructure. Its plans have gotten mixed reviews, from excitement to “not another set-top box.” Via the Internet, it can deliver YouTube or Comedy Central videos. The company calls this TV 2.0, which to me means it must be better than “I Love Lucy.”

The company faces a lot of competition. Apple TV is going to be more attractive now that it can get movies on the same day as they go on sale as DVDs. Vudu also has a lot of movies on demand available. Tivo’s Series 3 box can appeal to high-definition video junkies. AT&T is rolling out its DSL-based IPTV service nationwide, promising interactivity and movies on demand. And Digeo will have its Moxi boxes out later this year as well. It’s a crowded market and Sezmi will need big partners or a big advertising budget to overcome all the noise.

Since many of the cable and satellite providers already have their own set-tops, Sezmi is going to enter the market city-by-city as it signs up local TV station partners. A user will be able to press a button and log into the service, getting access to personalized play lists for music, recorded TV shows, and an archive of movie favorites. You can share your play lists with friends and family and rate shows.

The company says it has designed a powerful over-the-air antenna to pick up signals, even in areas where it’s tough to get digital TV or standard signals. Each set-top will have a terabyte hard drive, enough for 1,000 hours of video. The set can pick up free digital TV broadcasts of networks but could also use the digital TV airwaves for premium paid content. The company is going to have to sign content deals separately with TV content providers, such as Showtime.

Its co-founders include Phil Wiser, former chief technology officer at Sony’s U.S. division. The price hasn’t been set. But the company says it will start commercial trials in pilot markets with broadband service providers and national retailers later this year.

Last August, the company raised a $17.5 million round led by Morgenthaler Ventures and Omni Capital.