I find LaserDisc to be a fascinating format. The base format is analog, but the surface of the disc only has two possible states: a pit or a land, just like CDs. To make this work, the various analog signals (composite video, left analog audio and right analog audio) are frequency modulated with different carriers. This moves all the information into the frequency domain so the amplitude is no longer significant. The combined RF signal is then used to determine which areas should be a pit or land based on whether the signal is above or below zero.
The way digital audio was added is also interesting. It's based on audio CD technology which is a purely digital format using EFM (eight to fourteen modulation) to encode bits on the disc as pits and lands in a way that can be reliably recovered (direct encoding is problematic because you need a sufficient number of level transitions in order to do clock recovery and probably for some other reasons I"m not aware of). It turns out that there is a bit of unused RF spectrum below the lowest carrier of the analog signals. On NTSC discs this gap is almost big enough to fit CDDA EFM when viewed as an analog signal, so they basically just reduced the sample/data rate slightly to make it fit and then mix in the EFM to the analog RF as if it were another analog FM signal. On PAL discs, the gap was too small so one of the analog audio channels is sacrificed to make room.
The way digital audio was added is also interesting. It's based on audio CD technology which is a purely digital format using EFM (eight to fourteen modulation) to encode bits on the disc as pits and lands in a way that can be reliably recovered (direct encoding is problematic because you need a sufficient number of level transitions in order to do clock recovery and probably for some other reasons I"m not aware of). It turns out that there is a bit of unused RF spectrum below the lowest carrier of the analog signals. On NTSC discs this gap is almost big enough to fit CDDA EFM when viewed as an analog signal, so they basically just reduced the sample/data rate slightly to make it fit and then mix in the EFM to the analog RF as if it were another analog FM signal. On PAL discs, the gap was too small so one of the analog audio channels is sacrificed to make room.