Interestingly both Xiaomi and Blackview #Android phones will get quite near 25fps, old Xperia XZ3 forces video to near 30fps (so I decided not to use it)
#ShutterEncoder (a gui frontend for #ffmpeg available for mulitple platforms) can also conform variable frame rate #video by transcoding it back to H264 (or other suitable codec) and selecting conform in advanced features (*not* standalone conform function, that just changes metadata so doesn't work)
Also got a cheap #gimbal for the Xiaomi phones ( Blackview is too heavy for it), it works well without using the app as well as a pair of 2,4 GHz external microphones - these only work with the Blackview, but have *very* strong audio, to the point of clipping on loud sounds (which explains why so many youtubers have clipped audio)