RCW 42.56.010(3) defines "public record" to include any writing containing information related to the conduct of governing. RCW 42.56.010(4) then defines "writing" broadly to include (emphasis added):
handwriting, typewriting, printing, photostating, photographing, and every other means of recording any form of communication or representation including, but not limited to, letters, words, pictures, sounds, or symbols, or combination thereof, and all papers, maps, magnetic or paper tapes, photographic films and prints, motion picture, film and video recordings, magnetic or punched cards, discs, drums, diskettes, sound recordings, and other documents including existing data compilations from which information may be obtained or translated.
So while a video is not "writing" in the colloquial sense, bus videos are still a public record subject to production under the PRA unless an exemption or prohibition on disclosure applies. The extent to which exemptions or prohibitions on disclosure could apply depends entirely on what is contained on the video recording.