Twelve states—California, Connecticut, Florida, Illinois, Maryland, Massachusetts, Michigan, Montana, Nevada, New Hampshire, Pennsylvania, and Washington—require the consent of all parties for you to record a conversation..

say something like "Officer, I'm not interfering. I'm asserting my First Amendment rights. if recording something you are not a part of.
The lesson for you is this: If you want to limit your legal exposure and present a strong legal case, record police openly if possible. But if you videotape on-duty police from a distance, such an announcement might not be possible or appropriate unless police approach you. If you live in one of the 12 all party record states, you might say something like "Officer, I'm familiar with the law, but the courts have ruled that it doesn't apply to recording on-duty police."
since op lives in California i said she should mention it because some of the states have been ruling that this "law" is unconstitutional.