I assume we would like open source/freeware first and then move onto the paid stuff if it is truly necessary.
Your requirement for pausing/repeating/freezeframing sections places you pretty much squarely in non linear editor country -- youtube's thing is at player level from what I have seen. Trouble is open source full on non linear editing is of the "useful or easy -- pick one" persuasion with the timeline based stuff that most using the paid stuff get used to being nowhere to been seen for the most part*. If you want to convert or add very nice filters then carry on and the only thing that will ever trouble you is finding out if you are licensed to use the codecs but full on editing poses a greater challenge.
I know how I would do it but many do not agree with me that avisynth is simple (though as you are a programmer you might well agree that avisynth is the good stuff) and the other windows compatible freeware editors of note** in avidemux and virtualdub could potentially be troubled here unless you want to cowboy style it: both will happily duplicate a frame and insert it in the video for you leaving you room to sub and/or dub things as well as edit new sections into it, with the exception of virtualdub's mask function (which is a mask rather than a frame duplication) that is more of something you can do rather than "extend clip out and mask". Subtitle support comes in the way of support for all the nice subtitle formats which does allow you to do some great stuff but it is not quite at simple timeline type level where you could easily click and drag things around to give you more time when you want it and edit it all in house.
*If you are doing a timeline in avisynth it is because you are doing a timeline. If you do not want to be constrained to a timeline based workflow then avisynth will not make you.
**I have not really tried blender or VLC's video editor options as far as video goes in some time and tended to use avidemux on linux or just not properly edit stuff on it, now linux has avisynth/avxsynth I think I am mostly sorted there too so I have no checked out the rest (and there are quite a few).
After this we look to the commercial. Before going too far Windows movie maker, for as much as I usually deride it there is a reason it has got as many fans as it has and though its output options are shockingly limited (I only have the XP version in front of me but it did not get that much better as time went on) you can do an awful lot with it.
