I just cross-compiled ffmpeg with ac4 support. I used the following projects.
and
GitHub - rdp/ffmpeg-windows-build-helpers: Helper script for cross compiling some media tools for windows, like customizable ffmpeg.exe (with or without non-free components, etc), and some other bonuses like mplayer, mp4box, mxf, etc. (current build has a slight typo, there is a hashtag on the wrong line)
the command I used in ubuntu 24.04 is:
./cross_compile_ffmpeg.sh --ffmpeg-git-checkout=https://github.com/elliotclee/FFmpeg.git --disable-nonfree=n
I am running initial conversions still and will post back when done
ffmpeg/ffprobe builds attached