Hi @coolhandluke, thanks a lot for the info. I spent some time yesterday, trying different things, and I was not successful to get rid of that black poster attribute, it seems that what is happening, is that IE is briefly showing the image that is created as part of the data-poster attribute, and then switches to the video and there is a momentary time period where this blank frame is shown.
I have not found a workaround for this, it seems to be only affecting to IE 11. IE 11 by the way does render sites differently than other browsers and seems to have more issues with background video than other browsers, from the research I have done on the net.
Another option is to re-encode the video, it could be that IE does not like the encoding so well, so is showing that black space due to that. If you could send me the original video file, via we transfer or just email it to me, I will re-encode and do a test with that. I was able to reproduce the issue with the original issue (also Waldo did too) and now I want to test with a new re-encode.
Thanks in advance!