Streaming in MP3 format from the Klipspringer hub or using the MP3 encoding class in the codec library requires the LAME API to be installed. If you aren’t interested in streaming in MP3 format, just ignore warnings about it from configure, and install without LAME support.
On many systems, LAME API support is simple to install using the package manager. For instance, on Debian-based Linuxes (such as Ubuntu and Raspberry Pi OS), you can just enter
sudo apt-get install libmp3lame-dev
in the terminal. On macOS it’s almost as easy if you use Homebrew: use the command
brew install lame
If none of these installation methods works on your system, please refer to the official LAME website for other suggestions.