What is a subpack?
A release with a subpack generally contains an AVI file named something.dub.avi, an MP3/AAC with the Japanese audio and the subtitles with the endings ifo, idx and sub (all required for them to work, basically VobSub format). These were often played with MicroDVD player and the audio often went out of sync. Some releases also had small something.sub.avi files which were linked to the other files which made playback much better and simpler. They stop working if you install DirectX 8.1 or later, something you should do to make all the other files play properly.