Problems with sup and srt

[malimuc]

Does anyone know the reason why, when changing subtitles, it happens that they are not synchronized with the sound? Namely: I have a srt file that I am converting to sup. I replace the sup file in tsmuxeRGui, for example English SDH with Slovenian, and when I play a movie with the inserted sup file, the subtitles seem to be out of sync with the sound! If I do the same process, but instead of sup I insert srt, than is everything OK! What is the difference between sup and srt, even though 95% of the time the sup file works OK, but in some cases it doesn't?
Has anyone encountered similar problems? Maybe some explanation or help? This is happening when I try to editing full Blu-ray movies!

best regards

P.S.: To convert from sup to srt I use programm easySup v0.5

[cubicibo]

If your SUP file does not have the correct framerate set in the stream, tsmuxer will rescale its timestamps, this will cause a drift.

[StainlessS]

SubtitleEdit has a "Visual-Sync" thingy for retiming subs,
set time of first sub, and time of last sub, and hit "Sync" button.