Why do my .ogg and .mp3 music files play slowed down and the wrong pitch when imported?

This is caused by a bug* in SDL_mixer, the library we use to play audio files. The file might also play faster and a higher pitch. It occurs for audio files with less common sample rates such as 48kHz or 96kHz. To fix it, you need to manually reencode the file to 44.1kHz, using software such as Audacity. See Music Utilities. I believe 22050Hz also works correctly.

* Actually, it's a missing feature, SDL_mixer just plain doesn't support resampling to the rate needed by the operating system/hardware.