I received an email from Mike BlueHair, co-founder of Film the Police PDX. He confirmed what I found: filming the police is legal in Oregon, and added a few specifics about what’s allowed:

If you are someplace where there is no reasonable expectation of privacy. like any public building/bank lobby /hotel lobby/ red and black cafe Oregon is a one party consent state in regard to both audio and video recording. meaning you have the right to film anything you like in public. you may stand on public property like a sidewalk and film private property. that being said if your on somebodies property and they ask you to leave you have to leave or you could be arrested for Trespassing. this does not apply to public buildings of any sort!
Many officers don’t know the law, or as Mike thinks will try to “con you” into not filming them. In the beginning of the video, the officer tries to tell him that he can’t film people on their private property— and Mike firmly and politely tells him he’s wrong. Then at the end of the video (11:21), he asks the supervisor to tell the offending officer the law: Oregon is a one party consent state for audio and video, and he has the right to film people on private property. The video is very satisfying to watch…