Had to rebuild iTunes library and it won't accept most of the videos it previously had? Why?

Question

I'm having a strange problem with iTunes -
My boot hard drive recently crashed and took iTunes and my library with it. Fortunately I had all of the music and video files themselves backed up on another drive. When I reinstalled the OS and iTunes and then attempted to add all of the music and video files back into the new, blank iTunes, it accepted all of my music files but it kept crashing when I tried to add the video files back in.
The details: using a 24" iMac 2.4 GHz Intel Core 2 Duo with OS X version 10.9.4 both before and after the hard drive crash, and iTunes version 11.2.2 was my working copy of iTunes with all of my media files happily loaded in it's library, but the newly installed iTunes was at first 11.3.0 and now 11.3.1. Neither with version 11.3.0 nor 11.3.1 will it load all the video files into the library (haven't tried downgrading to 11.2.2, maybe I should? but we'll get to that in a minute).
I have about 300 video files of several different file types (.mpg, .mp4, .m4v, .mov) which over the years I had added to iTunes as I acquired them, and at the time of the hard drive failing, they were ALL in my iTunes library and I'd never had iTunes reject any file types. They all played fine as well as being a part of the library. And since I had added them over the years, they were added during quite a few different versions of iTunes as it was upgraded over time.
So, after I added all the music back into iTunes on the new drive, I attempted to add the videos all at one go, but it crashed after only 5 or so files being incorporated. Thinking it may have been too many at once, I tried adding them in smaller batches, but had the same problem. I took a look at what it had added before crashing each time, and found that every time it would load only mpeg 4 files, either .mp4 or .m4v, and would crash as soon as it encountered an .mpg or .mov. So I added all 50 or so of the mpeg 4's, and then tried adding the .mov and .mpg files individually and found that no matter which one it was, it was apparently the file type it didn't like, not the individual files themselves. Randomly trying about 75 led me to that conclusion, but I didn't try all 250, so I guess it's possible there might be some .mpg's it would take, however I only had about 10 .mov files and it won't take ANY of them. Considering all of these files regardless of their type were part of my old iTunes library for years and worked just fine, I don't understand why it won't take them again. I tried adding them by dragging them to the open iTunes pane, and by using the import command, and neither way works, all that happens is it crashes. Every time.
I tried converting these files to mpeg 4 types, and when I do that, it will take the converted version. However, a lot of them don't come out right when converting them, either the audio is messed up or the dimensions of the movie are incorrect and stretched or squished. It seems I could fix this problem by making sure every video file I add is an mpeg 4, but since I'm having so much trouble converting them properly and it's terribly time consuming, I was hoping someone would have insight into this strange, strange problem. I tried to see if this was a known issue with iTunes, that it only takes mpeg 4 files now, but I can't find anything about that. Anyone know if that's the case? And therefore hopefully an upcoming patch will fix it? Or is it just a weird, weird problem with me only?
Very frustrating, hopefully someone can help me out. Even if there's no apparent fix, maybe someone can recommend a good application for converting movie files that is easy enough to use for someone who's not familiar with the process, i.e. maybe it can auto-detect things like the audio quality and dimensions so it comes out right without me having to be a real whiz at it? Thank you all very much in advance for your help!

Answer 1

OK, so I have now found that this is apparently normal for iTunes, to only accept mpeg 4 movie files, all the searching I did before I must have worded it wrong because I couldn't find anything about this, incredibly. Had been looking for why iTunes won't take all the files it previously did, like if it had been changed, and it hasn't, it's allegedly always taken only mpeg 4 files. Also I had been searching for why iTunes crashes every time I try and add/import anything but mpeg 4 files, and even sometimes with mpeg 4 files. That isn't normal, it's supposed to just do nothing apparently as I've just found out. So for these reasons I didn't find the answer despite my searching all over the web.
So I guess that answers my own question now, but I'm still perplexed as to why I absolutely, definitely, without any doubt, had several hundred movies of a few different video file types loaded, accessible and playable in my iTunes library that everything here claims iTunes never accepted. It apparently shouldn't have been possible for me to have done this, but for probably 10 years it's been this way.
Perhaps since I don't remember adding these files to iTunes anymore recently than maybe 6 or 7 years ago, the iTunes back then did accept all kinds of file types? Or could I have somehow had some video codecs or software that expanded the capability of my movie players like Quicktime Player that unwittingly also allowed iTunes to take those files as well? All I know is somehow it worked! So now my question is how did I have it working before, so that maybe I can make it work again.