Now, two more set-top boxes have been launched to try to marry the Internet and the TV. Both adapters, from Sony (SNE) and Roku, worked well in my tests, but each has limitations. The problem is that one of the boxes supplies content from a wide range of Internet video sources, but only works on selected models of one brand of TV set; the other works on a wide variety of TVs, but only provides a single source of content.

Sony’s adapter is the Bravia Internet Video Link. This is a $300 module that attaches to certain Sony HDTV models. It can either be set up beside the TV or snapped onto the back of the set. Once it’s connected to your TV and to your home network for Internet access, a new menu appears on the TV allowing you a choice of videos from numerous online sources, including YouTube, Yahoo (YHOO), Blip. TV, Sports Illustrated, AOL, Wired, and the Web sites of CBS (CBS), Showtime and more.

Setting up the Bravia Internet Video Link was straightforward, even though it involved a welter of cables. There is no built-in Wi-Fi — you need either a cable or an add-on wireless adapter to connect to the Internet. The primary hookup to the TV is via a modern type of cable called HDMI, for High Definition Multimedia Interface.

I tested the Sony Link using the company’s most unusual HDTV set — a tiny, very costly model that uses a very thin, very vivid new screen technology called OLED, for Organic Light-Emitting Diode. This TV provided a spectacular picture, but it isn’t required to use the Sony module. The Link works on many larger, more common Sony sets with more common screens. It just doesn’t work on non-Sony TV sets.

Sony’s Bravia Internet Video Link adapter

The Sony module doesn’t have its own remote control. It uses the one that came with the TV. This makes for an awkward experience, because there are no standard play and pause buttons, and various other buttons on the remote meant to do one thing on the TV may do another when watching Internet video via the Link module.

Also, I found some of the Internet content to be disappointing. Many of the items labeled “movies” on various Internet channels were really just trailers, and some content was stale. For instance, some baseball news videos on Yahoo were weeks old.

However, Sony plans to make one of its feature films, “Hancock,” available through the Link module before it’s released on DVD. More important, it will be adding access to Amazon’s (AMZN) forthcoming video-streaming service, which promises to contain a wealth of full-length content.

The Netflix Player by Roku is much simpler. In fact, it was the simplest set-top box I have ever tested. It costs just $100 and does just one thing: It allows Netflix (NFLX) subscribers to view its movies and TV shows via the Internet on a television set instead of on a computer. It can’t get you any other video content from the Internet.

The Netflix player is a small, plain black box that works with most TVs, not just digital or high-definition models. It connects using both old-fashioned cables, like the kind used by many VCRs and older DVD players, or an HDMI cable.

Unlike the Sony, the Roku box includes both wireless and wired Internet connectivity, and has its own remote. While the box is capable of displaying high-definition content, the Netflix service isn’t currently streaming movies and TV shows in high definition, so you get varying quality, depending on your TV and Internet speed, up to DVD-type levels.

There’s no added monthly fee required to use the Roku box, but you must be a Netflix subscriber. The box merely displays the movies or TV shows you have placed in your Instant Queue on Netflix. You have to do this on your computer before viewing the videos on the Roku box. You can choose from around 12,000 streaming movies and TV shows, far fewer than the 100,000 titles Netflix makes available via DVD, but a sizable collection.

In my tests, the Roku box set up quickly and easily, the interface and remote were simple and effective, and the movies and TV shows I tested streamed quickly and without hesitation over my fast home Internet connection.

Both products are meant to promote sales of other things — Sony TVs and the Netflix movie-rental service. They do these tasks well, but neither is the breakthrough solution that will connect most TVs to most Internet video content.

Find all of Walt Mossberg’s columns and videos online, free, at the All Things Digital Web site, walt.allthingsd.com. Email him at mossberg@wsj.com.