"We value our broad developer community and therefore ask everyone to adhere to the same guidelines," Google added.
But Howard countered, saying that was not what Google had done. Instead, he slammed Google for playing favorites, arguing that Microsoft's app was no different from those sanctioned by Google for Apple's iOS —which powers the iPhone and iPad — or Google's own Android app.
"Google's objections to our app are not only inconsistent with Google's own commitment of openness, but also involve requirements for a Windows Phone app that it doesn't impose on its own platform or Apple's," Howard said.
The question of "openness" has come up before between Google and Microsoft.
In May at Google I/O, the company's developer conference, CEO Larry Page called out Microsoft for not reciprocating on API access and attacked "people milking off one company for their own benefit" as he referred to Microsoft's blocking others' ability to integrate with Skype.
"We certainly struggle with people like Microsoft," Page said.
For its part, Microsoft has long complained that Google won't give it the same metadata from YouTube that the Mountain View, Calif., company gives Apple and its iOS mobile operating system.
The antagonism runs deeper than YouTube, as the two compete in numerous key areas, including search, operating systems, business productivity software, and tablet and smartphone apps.
Microsoft hasn't been above the fray. It has repeatedly hammered Google practices in its months-long "Scroogled" campaign, most recently last week when an attack ad took aim at Gmail again.
But the YouTube blocking was a major escalation of the war between the two, Moorhead said.
"Larry's rant at Google I/O made him come off as a white knight," who was simply proposing reasonable open standards, Moorhead said. "But this makes that stance seem unbelievable."
Howard's blog post read like a legal complaint, with point-by-point refutations of Google's objections to the Windows Phone YouTube app. That wasn't lost on Moorhead, who noted the post was written by one of Microsoft's legal team.
In fact, Howard is head of the litigation and antitrust group, and as a deputy counsel, reports directly to Brad Smith, Microsoft's head lawyer.
Moorhead said Microsoft was signaling that it may take Google to court over the issue, perhaps using an antitrust angle. "Microsoft has a big point here," he said.
"It seems to us that Google's reasons for blocking our app are manufactured so that we can't give our users the same experience Android and iPhone users are getting," Howard said. "The roadblocks Google has set up are impossible to overcome, and they know it."
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