Larry my friend, believe it or not once I had the "process" in hand it was rather straightforward. Yet, it bamboozled me for nearly a year...so I am not bragging. Here are a couple of tips I learned from others on the forum.
1. Check the length of your video. There is a 100 mb limit and for my first one I kept very short 13.5 mb to make sure I was well under the limit.
2. WAIT,WAIT,WAIT - I, like you, was used to uploading pictures that happen almost instantaneously. I think I was cutting the process short by failing to watch the screen and WAIT for the process to finish. It took about 20 seconds, which seems like a long time when you are waiting, to upload the video into my reply box on the thread. Note...when it did that, I still thought that I had failed because the "black box" that appeared in my unposted reply would not open the video. Fear not, I found that you have to "POST" the reply first to see the result
3.After you post, you will see a message in the reply window..."Video is uploading (or some such)" and you have to WAIT again until that finishes and then finally your video is in the thread.
I am convinced that at some stage or another, being used to almost instantaneous response, previously I was inadvertently cutting the process off by hitting the "play" button too soon and thus stopping the upload. I plan to try some more just to see if I really can do it, but my final advice is be patient, and watch for the messages in the screen, it takes some time .