The spring Nielsen ratings show that 2.5 million fewer people are watching TV than a year ago. Instead, viewers are demanding content on every conceivable electronic device, including laptops, cell phones, hand-held computers and even gaming consoles.

For established video entertainment and equipment companies, adapting to new consumer habits presents something of a minefield. But for early-stage startups, that field is clear. With Brightcove Inc. of Cambridge, Mass., and other early online video infrastructure companies starting to hit puberty, fledgling tech players are emerging to fill the gap between making digital video available and making it widely and easily accessible.

The punctuation mark for these startups was Google Inc.'s $1.6 billion purchase of YouTube Inc., offering hope to other video players for lucrative exits. Despite the copyright and other legal issues hanging over the deal, the transaction underlined the urgent need to make video content more searchable and portable on a range of devices. Most video startups -- and there are dozens -- are in the early stage of development, having raised only a seed or Series A round, while many are bootstrapped.

To date, the sector has seen few acquisitions. But the size of the buyers searching out promising video technologies, ranging from Google to networking leader Cisco Systems Inc. and media giant CBS Corp., bespeaks the vast potential demand for startups that can stake a claim to the budding business.

To that end, following are 15 digital video startups to watch. Some, such as Kyte.tv and TargetSpot Inc., are narrowly focused, while others, such as BroadQ LLC and TVersity Inc., aim to disrupt an entire industry. All are undermining TV's primacy as an entertainment and advertising medium.

Pimp my console

So much for TiVo, Slingbox or any other set-top device that takes up coveted real estate in the entertainment center. The best device for controlling your TV may turn out to be the gaming console. By 2011, more than one-third of U.S. households will get their networked TV through a console, estimates market researcher Diffusion Group.

Several startups are already developing software that loads onto a gaming console to serve as a TV channel guide, along with organizing photos, videos and music stored on home computers and the Internet. Where they differ is in their business models. BroadQ in Austin, Texas, and TVersity in Tenafly, N.J., sell directly to consumers. By contrast, Avtrex Inc. in San Jose, Calif., hopes to convince large electronics makers to license its software and install it directly onto their networked TVs.

Of course, many TV viewers aren't waiting around for a networked set. They'd rather watch video on their cell phones or laptops, and even jury-rig their own Internet TVs. Cable and telecommunications giants may be ignoring the market for now, but several startups are solving the problem of how to stream huge video files, which can be 10 to 20 times larger than a still photo, quickly and without choking up the relatively scarce bandwidth coming into a home.

Startups that aim to develop techniques for efficiently delivering high-quality video over the Internet and home networks include Itiva Networks Inc. in San Francisco, which counts as customers Playboy Enterprises Inc. and EMI Music Canada; and Rinera Networks Inc. in San Mateo, Calif., which expects to have customers testing the service later this year. Meanwhile, Imagine Communications Ltd. in Cardiff-by-the-Sea, Calif., is developing an appliance for cable companies that compresses high-definition video.

What to watch

As programming proliferates, sorting through it all is sure to become challenging. To that end, Kyte.tv in San Francisco has its eye on creating TV channels for the Web. Currently in stealth mode with backing from the venture fund of Skype Technologies SA co-founder Niklas Zennström and with a recent investment from Nokia Growth Partners, Kyte.tv combines the ability to post video content with social networking.

Cleveland's YeboTV.com aims to broadcast live events, such as concerts, over the Internet. This is harder than it sounds because the Web is essentially a one-to-one delivery medium. That means when an Internet user clicks on a video, a server is activated to send the file. If many users click on the video at the same time, many servers are required to meet the surging demand. To get around this problem, YeboTV uses a proprietary streaming technology that connects people to a satellite network. Customers include indie bands, such as Madina Lake, while the company also plans to broadcast concert tours.

Viewers accustomed to free content on their TVs are expecting the same of video displayed on other devices. Enter the advertising industry, starting with ads that support video on cell phones. Zoove Corp. in Palo Alto, Calif., backed by Accel Partners, focuses on selling streaming video advertising on mobile phones.

Cell phones aren't the only hot ad medium, which is why New York startup TargetSpot, San Mateo-based Adap.tv and Cambridge-based ScanScout Inc. offer advertising over streaming media to any device, whether a phone, PC or TV set. ScanScout has a few online video customers that use its technology to offer relevant ads next to videos playing on the site. Meanwhile, TargetSpot plans to launch a video advertising service for local ad buyers this year and already counts CBS Radio Network as a customer. And as advertisers come increasingly to rely on Internet video, tracking who's watching what is becoming ever more important. Visible Measures Corp. of Cambridge aspires to be the Nielsen of online video providers, selling software to compile online viewing statistics.

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