Use & Build Vorbus audio:
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Vorbus audio provides aac like quality with open source tech, can be quite high quality and flexible but still providing lossy compression. Best bused when compressing already lossy audio like AC3 (on DVDs) or from MP3 or AAC to something open source.

To use:
ffmpeg -i A.mkv -c:v copy -c:a libvorbis B.mkv

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To build:
sudo apt install libvpx-dev libvorbis-dev libva-dev

git clone https://git.ffmpeg.org/ffmpeg.git ffmpeg
cd ffmpeg
./configure --enable-libmfx --enable-libsvtav1 --cpu=native --enable-vaapi --enable-nonfree --enable-opengl --enable-gpl --enable-libx265 --disable-vdpau --enable-libvorbis --enable-libvpx
make -j8
sudo make install
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Source:
https://stackoverflow.com/questions/19454509/ffmpeg-unable-to-find-encoder-libvorbis
https://trac.ffmpeg.org/wiki/TheoraVorbisEncodingGuide

Date: November 20th 2022