The best way to create high quality slow motion video is to work with original footage recorded at a high frame rate...
...The next best option is with software that uses optical flow techniques to create smooth 'slo-mo' from standard frame rate video clips. This can produce much better slow motion video quality than that obtained from the simple frame interpolation techniques used by many consumer video editing programs. - These can often produce quite 'jerky' results... especially at so called 'super slo-mo' rates..
Commercial options that use this 'optical flow' technique include Twixtor, Boris BCC and FCPX. These can all give excellent results, but have one problem in common - they are expensive!
You can however get comparable results by using free software that also uses 'optical flow' - MVTools
The clip below as an example of a 'slo-mo' video clip, made using that software...
One problem with using MVTools is that it uses text 'scripts', rather than a Graphical User Interface (GUI). So it does have a bit of a learning curve for those not familiar with this way of editing.
MVTools is a plugin for AviSynth, which also uses scripts. Scripts are often described as being a difficult way to edit video, but they can be quite simple to use, once the basics have been mastered - and it's no where near as 'scary' as some folk would have you believe!
These pages are only intended to provide a simple guide on how to use the parts of AviSynth and MVTools required to create high quality 'slo-mo' video clips.
If you are interested in learning more about other AviSynth functions - of which there are many - there is lots of information already online....You could start HERE for example.
The pages linked to from the headings at the top and bottom of this page will describe a simple way of using MVtools - in conjunction with other free tools - to add accurately timed and smooth slow motion edits to your video clips.
Start by clicking on the 'Setting up Virtualdub' heading below - or at the top of the page...