recordvanilla
In odamex, this will record a vanilla doom demo.
Ex. If you wanted to record a demo of a map01 run, you would use recordvanilla map01 demotitle
You can also run odamex with "+recordvanilla map demoname" on the commandline
recordlongticks
This is like recordvanilla, only it records demos in the longticks format. Consult the Doom Wiki.