@poisondeathray
LWLibavVideoSource helps indeed. The framerate is fine.
It was downloaded with AnyStream. No other adjustments. So I started to clickthrough StaxRip and ran into the issue. Wondering why it takes so long and files size gets unfamiliar high
Other files, received the same way, are fine, using LSMASHVideoSource.
EDIT: I see, I can change the Source filter to LWLibavVideoSource in StaxRip. Still wondering, because unter Settings -> Video there is a check for "Add filter to automatically correct the frame rate", would expect an AssumeFPS here, because the Logfile shows a difference in "Media Info Source File" = 23.976 and following "Source Script Info" = 1.5321345
Anyway, if it something normal, thank you for the hint.