California's wiretapping law does not apply to conversations in public where the persons being recorded do not have a reasonable expectation of privacy, It also does not apply to police who are public officers in their official capacity. Only private conversations where an expectation of privacy exists require dual consent. It is perfectly legal for you to record a traffic stop for instance, and the cops are probably recording it anyway.
California's wiretapping law is a "two-party consent" law. California makes it a crime to record or eavesdrop on any confidential communication, including a private conversation or telephone call, without the consent of all parties to the conversation. See Cal. Penal Code § 632. The statute applies to "confidential communications" -- i.e., conversations in which the participants have an expectation of privacy. A California court has ruled that this statute applies to the use of hidden video cameras to record conversations as well. See California v. Gibbons, 215 Cal. App. 3d 1204 (1989). If you are operating in California, you should always get the consent of all parties before recording any conversation that common sense tells you might be "private" or "confidential." In addition to subjecting you to criminal prosecution, violating the California wiretapping law can expose you to a civil lawsuit for damages by an injured party. See Cal. Penal Code § 637.2.
Conversations that occur in a public space or in an area where the parties do not have any expectation of privacy are not covered by the wiretapping statute. Therefore, you generally are free to record a conversation happening between people in a public place, such as a street, a park, or on the steps of a courthouse, even without consent. For example, a California court has upheld a television network's right to use a hidden camera to videotape a conversation that took place during a business lunch on an outdoor patio of a public restaurant. See Wilkins v. NBC, Inc., 71 Cal. App. 4th 1066 (1999). The court held that because the information being recorded was not secret or confidential, the statute was not violated, and the network was free to videotape.