If you have Audacity 2.1.0 and these files are MP4, M4A, MOV or ALAC, they won’t show up as waveforms unless you also install the optional FFmpeg library. Please see Audacity 2.1.0: FFmpeg required for MP4/M4A/MOV/ALAC import for how to install FFmpeg.
This is already fixed, so the next 2.1.1 release of Audacity should not have this problem.
Gale