The PQ subcode that gets burned to the cd lead in contains various information. Basic start and and times, pause time. It is what the cd player uses to find where everything is. There are other things such as ISRC codes that can be added as well.

ISRC codes were created so the record compainies can track how often and where there material is being played as far as radio stations.

These 12 digit codes are created by the record companies and are also supplied by them.

These are not mandatory but most major label releases will include them.

Is there anywhere I can read up more on ISRC codes and how they work?

What about newfangled CD-text?