It looks like there are some ffmpeg forks that include patches supporting AC-4 but they haven't been merged upstream yet. https://trac.ffmpeg.org/ticket/8349 ht

It looks like there are some ffmpeg forks that include patches supporting AC-4 but they haven't been merged upstream yet. https://trac.ffmpeg.org/ticket/8349 https://trac.ffmpeg.org/ticket/8349 Not that it changes anything. Proprietary formats have no place in such government specifications. But possibly a relevant ffmpeg build could help you do what you wanted to.