Several projects are underway to create music testbeds to suit the needs of the music analysis and music information retrieval (MIR) communities. There are also plans to unify testbeds into a distributed grid. Thus the issue of audio file formats has come to the forefront. The creators of a music library or MIR testbed are confronted with many questions pertaining to file formats, their quality, metadata, and copyright issues. We discuss the various formats, their advantages and disadvantages, and give a set of guidelines and recommendations. This document is a positional paper. It is intended to foster discussion and not as a definitive statement. Nevertheless, it is hoped that the proposals put forth here may serve as a guideline to use in construction of an MIR evaluation testbed.