subtitles do not sync after permanent writing

[srckaimal]

I download movies and write permanent subtitles to them using Virtualdub and vobsub without much difficulty.First I get the subtitle from subscene(usually) and then check it in the VLC player and if it is in sync write them permanently.
But sometimes after writing them, when I play the AVI file in the same VLC player it is out of Sync!
What can be the reason and how can I prevent it?
Please help.

[jagabo]

Use a better source filter in VirtualDub to make sure it gets the video frame rate right.

[srckaimal]

Thank you for the reply.But how can I do that?

[jagabo]

Get an appropriate import filter for the file type you're opening. Put in in VirtualDub's plugins folder. Then use that filter when you open the source video ("Files of type" pulldown in the "Open Video File" dialog).

https://www.videohelp.com/tools/Virtualdub