Hi
You seem to be using version 3.041 which is the latest incarnation of VP (That's my number..It's actually labelled 3.04)
As far as my comment re: emptying the cache. I referred to this only in the context of trying to load a project from an earlier version of VP and doing it BEFORE you try loading the .vpj file. A bit like starting with a clean slate. The cache is regenerated.
If you did EMPTY the cache completely (i.e. opened it and deleted the ENTIRE contents) then it takes quite a bit longer to regenerate the files when the .vpj file is loaded. Subsequent loading of the project though will be appreciably faster.
If your project has loaded already as seems to be the case from your video, then the cache will be largely up to date although it will continue to load items as they are generated like thumbnail data etc. This means that the for the section being treated the preview is not available. Note that tthe cache MAY also contain other files relating to older DIFFERENT projects whcih may slow things down.
This is why in 3.04 and later, clearing the cache using the option within the program will only remove the files that are not being used in the current project.
I do notice however that you seem to have a lot of clips in your video judging by the position of the scroll bar to the right of the media list window. It's normal, of course to have many clips in a project but I think this may be the crux of the problem with this version. VP has to generate all the thumbnails for these, save them to the cache, print them in the media list window instead of icons. Generate all the thumbnails required to display regularly in the sequence line instead of the landscape icon, set up all the transitions etc. and etc.
As Borate mentions, this is pretty labour intensive for the PC and can take an appreciable time particularly with the larger format HD videos.
I would suggest you try using the earlier version. (2.41)which is decidely faster. Unfortunately you have probably created your current project with 3.04 and saved the .vpj file. This will not now load in 2.41 as I noted in a previous post.
However. If you WANT to try this, and it will mean starting from scratch..I think you will find it will work OK.
Load version 2.41
Use "Any video converter" to convert all your clips to MPEG2 clips (keep them at the same size) I find these are much faster than the HD MPEG4 clips I get from my camera.
Load these to VP and redo the video.
Things will load and save much faster and you shouldn't get any "Waiting for preview" prompts (or hardly any)
You can see the green bar moving quicker and your video will preview almost straight away and the end result looks OK.
Nat