Someone re-parented a variation to prevent it being public domain until 2040.
So the variation cannot be used. That’s irrelevant for a file format. Some company could, for example, patent a more efficient encoding technique but the resulting file format is still public domain. So at worst an open source encoder would need to be slightly inefficient because it uses the traditional technique.
How? If the tech is older than 25 years, it’s prior art no matter what. MP3 is fully free for the same reasons.
Happened recently with a 1995 patent by a Stratasys, on a stronger technique for 3D printing using a brick infill method.
Someone re-parented a variation to prevent it being public domain until 2040.
So the variation cannot be used. That’s irrelevant for a file format. Some company could, for example, patent a more efficient encoding technique but the resulting file format is still public domain. So at worst an open source encoder would need to be slightly inefficient because it uses the traditional technique.
This is why we can’t have nice things…