The MPEG2 Standard is defined in ISO-13818, which is comprised of the following documents (some of them are also published by ITU):
- ISO-13818-1 aka ITU-T H.222.0
- Systems (definition of the MPEG2 Stream Formats, the decoder model and the timing/synchronization model)
- ISO-13818-2 aka ITU-T H.262
- Conformance testing (read if you want to write a multiplexer or an encoder)
- DSM-CC (Digital Storage Media Command and Control, used to transmit MHP applications and other data
- Advanced Audio Coding (AAC)
See ISO for a full list of MPEG2 standards documents.
You can buy all these documents from ISO, however they are quite expensive.
As the MPEG2 Standard is a superset of the MPEG1 Standard, you will find that it refers to the MPEG1 standards douments (this is especially true for audio coding). You might need to read ISO-11172, too.