4K video (4096 px wide by 2160 px high) is the cutting edge video format to offer your customers. You could use this as your transcoder source but as you've probably noticed the file size is quite huge and would take a very long time(4-8 times as long per format) for the set to be created using the transcoder. Our suggestion for now is to upload the 4K file as a downloadable format(You can create a new media type that is not embedded so the system can link to it) and for you to create a 1080p @ > 8000K bitrate MP4 version that you use as your transcoder source as you normally would when uploading a new set into the 'source' folder.
Currently there is little support to stream a 4K video file because of the incredible bandwidth requirements. Eventually web browsers will support playback of the 4K streams when the adoption of the H265 codec is implemented for playback in web video players. Until then your members will need to download and playback the file on whatever medium/player has support for it(VLC player, DIVx Player, Media Player Classic)
Let us know if you have any other specific questions regarding 4K video and support for it.
