You stated "Only codecs developed from the ground up by free software groups like Xiph are completely patents free"

I am fairly sure you would not be able to file a defensive software patent if a third party already has filed patents covering the same method since there would be prior art invalidating your newer patent application.

Given the number of software patents and their broad coverage, it is fairly unlikely that any method of producing a codec has not already been fully covered by issued software patents.

rgds