In one federal court, Microsoft has filed a patent-infringement case against TiVo, and in another to intervene in a dispute between TiVo and AT&T -- setting the stage for a legal battle over some of the most popular features used to watch television on digital video recorders. 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. And in another filing in that case (PDF, 10 pages) Microsoft denies TiVo's claims and asks the court to dismiss them. 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 user to store selected television broadcast programs while the user is simultaneously watching or reviewing another program."