trying to correct jerky video- help please!

I recently downloaded an HD video only to discover that upon playing, there
was frequent jerkiness. It's difficult to describe, but several times a
minute during play there will be a short (some milliseconds) sudden movement
or freeze. The video is watchable, but this is bothersome and I want to try
and correct it. What was strange was that none of my FULL HD videos showed
this, even though all were flv and with the same codec as the standard HD,
then I seemed to find the culprit: the standard HD vids had a different
frame rate than the Full HD ones. The FULL HD's, at 24 fps, play smoothly
with no sudden jerks, however the standard HD's are at something like
23.8something. I tried using AVIdemux and did direct stream copy except to
change frame rate from native 23.8 to 23.5 (the program chose the 23.5) and
this seemed to get rid of most of the jerky movements and I offset the audio
slightly figuring it would do the trick. However the closer to the end the
video came, the more out of sync the audio became. Now I'm not sure how to
proceed and ask for any help or advice. All I want to do is take these
originals and get rid of the jerkiness and retain original quality. These
originals are FLV's and I'm just keeping them that way until I can get rid
of the jerkiness.

Thanks in advance for any help.

Bill