A federal judge in Washington state has invalidated more than a dozen patent claims in the case of Microsoft v. Motorola.

Right now the winner (of this particular skirmish) is Microsoft over Google-owned Motorola Mobility.

On Wednesday, Judge James L. Robart of the U.S. District Court for the Western District of Washington in Seattle, issued an order in favor of Microsoft, invalidating 13 patent claims.

Those claims are in reference to just three patents (U.S. Patent No. 7,310,374, U.S. Patent No. 7,310,375, U.S. Patent No. 7,310,376) -- all of which have to do with encoding and decoding digital video content.

Microsoft had petitioned that the "means for decoding" and the "means for using" elements of the patents in question be declared as invalid based on a specific U.S. patent law specification, and the court has consented.

Following up a detailed technical analysis of the petition, here's an excerpt from Robart's order explaining his decision:

Finally, as stated, decoding and encoding are entirely different functions. Thus, even were a person of ordinary skill in the art able to devise an algorithm for decoding the function from the disclosed encoding description, that alone does not rescue the disputed means limitations from indefiniteness. Were that the case, any means-plus-function limitation could be saved from indefiniteness by an expert's testimony that he or she could have written computer code to perform the recited function based on unrelated disclosures in the specification. The specification needs to provide a decoding algorithm from which to base the understanding of one skilled in the art, and the court can find no such algorithm within the specification. Instead, the "means for decoding" limitations claim all corresponding structure under the sun by expansively defining the function in the specification as anything that decodes digital data. This definition renders the "means for decoding" limitation invalid for indefiniteness.

However, there are still more claims related to this trio of patents waiting for a ruling.

FOSS Patents' Florian Mueller explained a bit further, predicting on Thursday that these claims could also still be denied.

Most patent claims are actually invalidated for anticipation (lack of novelty) or obviousness (lack of inventive step over the prior art). Such questions can be decided on summary judgment but most of the time are put before a jury, while indefiniteness is for a judge to decide.

Mueller added that if any of these claims are upheld in Motorola's favor, Microsoft still might have a chance to license them under FRAND (fair, reasonable, and nondiscriminatory) terms.

For a full look at the judge's order, scroll through the document below:

Microsoft v. Motorola: Order Invalidating Patents by

This story originally appeared on ZDNet under the headline "U.S. judge rejects 13 Google-Motorola patent claims against Microsoft."