Sometimes you can eliminate problems by opening a file with a particular program, and then getting that program to regenerate/recreate and then save the file. The process of regenerating the file has the effect of cleaning the file, because the program starts from scratch and completely recreates the file from what is shown on the screen.
I have seen this trick work with Adobe Acrobat files. I had a huge document (over 100 pages) that simply would not print. I had Adobe Acrobat Pro, so on a lark, I decided to print the file to Adobe -- that is, to create a new PDF file from the existing PDF file. Adobe then completely recreated the file from scratch, saving the new file under a new file name (I did it that way rather than overwriting the original file). I was now able to open and print the new file.
Perhaps there is a video editing software that will read your video file, then recreate it into a new file. If you save it to a format other than MP4, it will have to recreate it from scratch, because it will have to convert every detail of the file into the new format. I think that is your best chance of cleaning up the file. Once you have cleaned up the file in this way, you should be able to then edit the newly-generated file as needed.
Make sure you make a backup copy before doing this, in case this process corrupts the file even more.
