According to the Reporters Committee for Freedom of the Press' First Amendment Handbook, twelve states forbid the recording of private conversations without the consent of all parties. Maryland is one of them.
And now a guy who was recording his own antics on a motorcycle is facing a felony charge because he continued recording during a traffic stop. David Rittgers has more on the Cato@Liberty blog.
Laws that ban all surreptitious recording to get at wrongful recording are overbroad and damaging. Laws that prevent the recording of police officers are particularly wrongheaded. Maryland needs some technology liberation.