I can understand the issue with trying to avoid video uploads. I think HTML5 might be the way to go and avoid plugins. There’s an example of using HTML5 to play local video here with source code.
There’s also Flowplayer (flowplayer.org) an embeddable HTML5 video player which supports local files here (demo http://demos.flowplayer.org/scripting/filereader.html)
You might try contacting other developers using Cesium, who have integrated video, such as Power Tracks who uses HTML5 as explained in the blog here
There’s some related developer discussion here
Hope this helps