Can't transfer movie from camera roll to ANYWHERE !!!

I filmed my child in a school production on my iPhone 6s Plus. The movie file is ~40 minutes and ~820MB. I can view it on my iPhone with no problem, but I can't transfer it from my iPhone to ANYWHERE ELSE!!!

1) tried sending to YouTube (this is the end goal so that the rest of the family can view it). Try to send it directly from camera roll and I get a "Video is Too Long" error. No problem, since I have a verified YouTube account. Go through Safari (and Chrome -- tried both) and it compresses the file, then gives a "File Type Unknown" error and won't upload. Same problem when using the YouTube App. Same problem when using Capture app

2) tried sending the movie file to Dropbox. I have ample space on my Dropbox folder for the movie (over 2GB available). I go through the Camera Roll and select Send to Dropbox. It says "An Unknown error occurrd" and won't go any further.

3) tried copying to my Mac (Macbook Air, El Capitan (latest upgrade), connected via USB) with Photo. The movie can be selected, but it gives and error when trying to copy it to the computer (I can't remember the exact error but it's file format related -- I'll have to check exactly what the error is when I get home tonight).

4) tried copying to Windows 8.1 PC (again through USB). I mount the iPhone, Allow Access to the computer, and then browse Apple iPhone > Internal Storage > DCIM > 100APPLE . All of my videos and pictures are present -- except for the one that I am interested in. It is still on the iPhone (I can go into the camera roll and view it while it is hooked to the PC, as with all the other images/movies), but it isn't visible. I do have another large movie that I took earlier (~675 MB), and it is visible to the PC.

I'm really stumped on how to proceed next. I don't want to have to snail mail my phone to each member of the family so that they can watch it . Any clues on what to try next?

Thanks.