I recently tried to build Haiku and got this error 
" ../src/add-ons/media/plugins/ffmpeg/AVCodecDecoder.h:21:18: fatal error: avcodec.h: No such file or directory
   21 |         #include "avcodec.h"
"
I am building it on void linux and it was building before like  a week or something. also I am sure I have this header file installed it belongs to ffmpeg-devel package. I also tried #inlucde "libavcodec/avcodec.h" and it didn't work although my language server correctly identified it.