check src/mpcdec and src/tremor. The latter we _don't_ currently have in tree, but might be a good idea to add for this (and maybe others).
From package.mask # Samuli Suominen <ssuominen@gentoo.org> (17 Oct 2009) # Obsolete Musepack SV7 format support. Install # media-sound/musepack-tools for libs and tools to convert # your audio files to SV8 format. media-libs/libmpcdec The mpcdec in muspack-tools is not compatible with mednafen