AC-3 does not offer lossless mode, only the extension TrueHD, which is still covered by patents. As mentioned in the article, AC-3 is pretty horrific by modern

AC-3 does not offer lossless mode, only the extension TrueHD, which is still covered by patents. As mentioned in the article, AC-3 is pretty horrific by modern standards. Use Opus or FLAC instead.