In 38 of the 50 states it is plainly allowed to record police, as long as you don't physically interfere with their work. Police might still unfairly harass you or ask you to stop but you will not be charged for illegally recording police.
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. However, all but 2 of these states-Massachusetts and Illinois-have an "expectation of privacy provision" to their all-party laws that courts have ruled does not apply to on-duty police (or anyone in public). In other words, it's technically legal in those 48 states to openly record on-duty police.
A lawyer in North Carolina was recently stopped and police did not think he knew his rights. Watch his footage here...https://www.facebook.com/BrockLawOfficesPC/posts/1363503737044947