Microsoft has filed a patent-infringement case against TiVo in one federal court and asked to intervene in a dispute between TiVo and AT&T in another federal court -- setting the stage for a legal battle over some of the most popular features used to watch television on digital video recorders.

The situation arises from a lawsuit filed by TiVo against AT&T last year in federal court in Texas over the telecom company's U-Verse system, an IPTV television service based on Microsoft's Mediaroom technology. TiVo alleges that AT&T's system violates three of its patents for commonly used DVR features, including one for a multimedia time-warping system that "allows the user to store selected television broadcast programs while the user is simultaneously watching or reviewing another program."

In a filing in that case late last week (PDF, 17 pages) Microsoft said the disputed features come from Mediaroom. According to the filing, AT&T has demanded that Microsoft indemnify it in the case.

"That demand has created potential exposure for Microsoft to the damages Plaintiff seeks to recover from AT&T Inc. for the alleged use of Microsoft software in connection with U-verse. Microsoft should be permitted to intervene and protect its own interests first-hand," the filing says. "Moreover, because Microsoft has customers other than AT&T Inc.’s subsidiaries that use Mediaroom, Microsoft should be permitted to eliminate in a single action the cloud of uncertainty that Plaintiff’s infringement allegations have cast over Mediaroom software."

The two other TiVo patents at issue in the case involve an "automatic playback overshoot correction system," and "a system for timeshifting multmedia content streams."

In another filing in that case (PDF, 10 pages) Microsoft denies TiVo's claims and asks the court to dismiss them.

Separately, Microsoft this week filed suit against TiVo in federal court in San Francisco, alleging that the company's technology infringes on two of its patents: A "system and method for secure purchase and delivery of video content programs"; and "a system for retrieving and displaying programming information in response to selection of a category of programming information."

Here's the full text of that Microsoft lawsuit: PDF, 53 pages.

In a statement this morning, Microsoft spokesman Kevin Kutz said the company "is open to resolving this situation through an intellectual property licensing agreement, and we have initiated discussions to engage TiVo in negotiations." We've also left a message with a TiVo spokeswoman seeking comment.

Five years ago this month, Microsoft and TiVo announced a partnership to let people move content from TiVo boxes to Microsoft-powered devices. I've asked Microsoft if that agreement is now expired, and whether it included any patent provisions.

Bloomberg News first reported on the Microsoft-Tivo dispute last night.

Update, 8:30 a.m.: Here's TiVo's statement:

"Microsoft's recent legal actions, including its decision to seek to intervene on behalf of its customer, AT&T, and its recent complaint against TiVo in U.S. District Court, Northern District of California do not bear on whether the AT&T products and services that are the subject of TiVo's complaint infringe the patents asserted by TiVo. Rather these actions are part of a legal strategy to defend AT&T. We remain confident in our position that AT&T will be found to infringe on the TiVo patents asserted."