The subject has been discussed several times. Please take a look at
this thread.
There were some other attempts to correct line sync jitter (linked in the thread above). I have tested all of these functions - they are very vulnerable to noise which is an element of VHS recordings. Sometimes the resulting line jitter after correction is bigger and more random than that of the input video.
I do not know if someone has tested using a
cross correlation function to find the beginning of a line which might reduce the influence of noise.