What is the Block Mode (optical)

A block is recorded in a certain mode:
Audio, M1, M2, M2F1, M2F2, DVD mode

On CD all Blocks contain 2352 bytes.  This is what you end up with if you extract raw.  Depending on the Mode, the user data portion is different.

Furthermore, every block is accompanied by 8 subchannels.  Each subchannel can contain 12 bytes.  The P and Q subchannel bytes are the most important and contain data necessary for correct operation.  They are tampered with the most in case of copy protections.  The other subchannels can contain data but are seldom used and not many CD readers can actually correctly retrieve all that data.  CD-Text is located in the subchannel bytes in the lead-in.

On DVD the story is completely different.  DVD only knows one Mode (DVD Mode)