FFMS2 is only slightly inaccurate in that it is off by half a frame, but depending on the current framerate, the delay may be huge. Take the following example:
Code:
frame number timecode (in ms)
0 0
1 1000
2 2000
3 3000
If you set the fpsnum to 1000 and fpsden to 1 (basically 1000 FPS), frame 3 would show up at time 2500 ms. While this is an extreme example, it is still off by 500 ms. Dss2 is off by 1 frame meaning frame 3 would get a time of 2000 ms.
As to why not a bug report, well I didn't want to wait for it to be fixed, but I can write one if you want. I also had fun programming this, so might as well. Another thing was I couldn't tell if the framerate I choose in FFMS2 dropped frames or not.