Q: I’ve recently discovered a problem when adding music files into my iTunes Music Library from elsewhere on my computer. I’ve used both “Add a song” and “Add a file”, but there are cases when not all of the songs transfer. I see the missing song in my selection when I attempt to “Add a song” but it simply will not populate into iTunes. Why?
A: Unfortunately, there are some file formats that iTunes simply refuses to pay attention to. iTunes will exhibit this exact behavior if the song in question is in an unsupported format like Ogg Vorbis, FLAC, Protected Windows Media Audio, or Real Audio. Note that if the song is encoded in unprotected Windows Media Audio, iTunes will import it, converting it on-the-fly to either MP3 or AAC.
How should you proceed? You’ll need to use another program to either (1) convert the audio into a format that iTunes will accept (mp3, AAC, Apple Lossless, AIFF, WAV, etc.), or (2) burn the offending files to an audio CD so that iTunes can import them on its own.