Executei os seguintes comandos para obter o ffmpeg no Kali Linux como root. Peguei o link do tutorial emEsse link
sudo apt-get build-dep ffmpeg sudo apt-get install libfdk-aac-dev sudo apt-get source ffmpeg
O erro vem depois do último comando ( sudo apt-get source ffmpeg
)
Abaixo está a saída completa
dpkg-source: info: extracting ffmpeg in ffmpeg-4.2.2 dpkg-source: info: unpacking ffmpeg_4.2.2.orig.tar.xz dpkg-source: info: unpacking ffmpeg_4.2.2-1.debian.tar.xz dpkg-source: info: using patch list from debian/patches/series dpkg-source: info: applying 0001-avcodec-arm-sbcenc-avoid-callee-preserved-vfp-regist.patch dpkg-source: info: applying 0002-avcodec-libtwolame-fix-mono-default-bitrate.patch W: Download is performed unsandboxed as root as file 'ffmpeg_4.2.2-1.dsc' couldn't be accessed by user '_apt'. - pkgAcquire::Run (13: Permission denied)