v0.4.3: Missing implementations when compiling

[rand00]

I installed ffmpeg through opam, which gives me version 0.4.3. I just depend on ffmpeg in my dune file, but get the following error when compiling:

$ ./install.sh
Error: No implementations provided for the following modules:
         Avutil referenced from bin/clients/n/.n.eobjs/native/n.cmx
         Avdevice referenced from bin/clients/n/.n.eobjs/native/n.cmx
         Av referenced from bin/clients/n/.n.eobjs/native/n.cmx
Done: 524/529 (jobs: 1)ERROR

This happened both on 4.11.1+flambda and 4.07.1 - and I'm running arch linux