For libav-stable, we download the Libav tarball, which is failing, because their certificate is broken: ERROR: cannot verify libav.org's certificate, issued by `/C=US/O=Let\'s Encrypt/CN=Let\'s Encrypt Authority X3': Issued certificate has expired. I don't intend to support Libav's overly old releases anymore anyway, so if you want to use Libav, use its git master.