rvm:
Suppose we wish to change the framerate from a video's default (say, 30 fps) to a slower framerate (say, 25 fps). If we insert the option "-fps 25" in Option--Preferences--Advanced--Mplayer/mpv--Options, hit Apply and then OK, the framerate clearly changes when the video starts to play again, but the Status Bar does not update to show the new framerate; the default framerate continues to show. Only a restart of SMPlayer changes the Status Bar framerate to 25 fps.
There also seems to be an issue with playing videos that have portions that are in slow motion. SMPlayer--or maybe MPV--doesn't seem to handle slow-motion well. Sometimes the video just hangs up, sticks on a single frame. Unfortunately, I can't seem to get a handle on just what's going on. If I do, I'll get back to you on it...