I was uploading a video at YouTube but my internet connection was interrupted and PC was shut down. I turned on PC and when my internet connection was restored, I opened YouTube Studio and saw that 91% of the video was uploaded. But the YouTube studio gave me options to cancel upload or delete the video. I had the impression that it already picked up the file again and started uploading from where it left off. I waited for few minuets but the progress was still at 91% uploaded.
If you are in the middle of video upload and PC gets shut down, power is interrupted or internet connection goes off and your video remains half uploaded, you can just start the progress from same level.
I did not started the upload process from zero. This is what I did to continue upload process even when my PC was shut down and internet was interrupted.