In this task, you are given a question and a context passage. You have to answer the question based on the given passage.
Q: What legal blocks are not a concern in the text, Context: There are also open compression formats like Opus and Vorbis that are available free of charge and without any known patent restrictions. Some of the newer audio compression formats, such as AAC, WMA Pro and Vorbis, are free of some limitations inherent to the MP3 format that cannot be overcome by any MP3 encoder.
A:
patent restrictions