Play from current transcode if same video requested from two clients

[lazyboy0172 7]

Currently if two clients request the same video on the server the server transcodes the video twice at the same time. This is further complicated when two clients request the same tv channel through embytv; emby requests the same channel on multiple tuners. This process could become much more efficient if Emby was able to recognize that the requested video was currently being pushed elsewhere and pushed the same transcoded videos through to the new client. At the very least this would be a more efficient way to handle multiple clients for the server, and would also include a side benefit of being able to push the same tv stream through embytv to multiple clients around the home, allowing the same channel to be broadcast around the home while only taking 1 tuner- great for football season!