In HD DVD, there are two ways to figure out which subtitle or audio track the user has chosen. The selectedAudioTrackNumber (and selectedAudioLanguageCode / selectedAudioLanguageCodeExtension) properties refer to the track (language) that the user has selected, but they may or may not represent the currently-playing track / language. The currentAudioTrackNumber (etc.) refer to the track that is actually playing right now. The same goes for subtitle tracks.

The different sets