macronencer,
First:Disclaimer, I am just experienced enough with video to be dangerous.(been messing with it since Win3)
SHS is not a video editor. As you have learned, you cannot change the frame rate inside SHS. You would have to use a Video editing program to re-encode the fila at a different frame rate. This is a very elaborate process.
The AVIs I have seen and made are locked at 29.97fps(NTSC-US standard). Are you working with PAL files?
I have seen mpg. and WMV files at 25fps.
If you import a 25fps file into SHS, it will recognize that. Use the Frames setting on the big clock. If you use the SMPTE setting, it is timing at 30fps, even though the actual video file may be different, at least from what I've seen.
"Just discovered something else FYI: This is purely and simply a calculation error. If I switch to "frames" mode then it says (for example) "50" at 2 seconds. "
This is not an error. If you are playing a file at 25fps, of course you would see 50 frames at 2 sec.
If you must work with 25fps files, use the Frames timer.
I was able to get a 1 frame error at 6 minutes on a test file. I attribute this to variations in equipment, encoders, etc.
If you zoom in horizontally on the tracks, you can pinpoint an event farly precisely.
Do you have any video editing software? If so, I might suggest rendering a work copy of the video with markers in an overlay video track.
Insert a white frame or something to mark critical spots.Hope that helps some.
You are delving into a challenging area .Best of luck to you, and keep it fun.