/usr/lib/x86_64-linux-gnu/pkgconfig/libavcodec.pc is in libavcodec-dev 7:2.8.6-1ubuntu2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/pkgconfig/libavcodec-ffmpeg.pc
/usr/lib/x86_64-linux-gnu/pkgconfig/libavcodec-ffmpeg.pc