MusicLibraryConverter is a software written in Python 3 for batch converting of a music library containing flac files to mp3. It retains all meta tags and can be used iteratively. It uses multi-threading and is based on ffmpeg (Windows) or avconv (Linux) as conversion backend and mutagenx as tagging library. Note that ffmpeg.exe/avconv must be available and it must be possible to find them via the PATH environment. The Python 3 library mutagenx (https://pypi.python.org/pypi/mutagenx/1.22.1) must be installed.