The general rule of thumb is ~2000 points on passmark per 1080p transcode for a dedicated machine. An 4th gen i5 NUC should be OK for 1 1080p stream or perhaps 2 720p streams simultaneously. I dont think the 5th Gen will be drastically different.
Edit... dont know why I didnt check if there was 5th gen scores...
http://www.cpubenchmark.net/cpu.php?...0U+%40+1.60GHz
http://www.cpubenchmark.net/cpu.php?....30GHz&id=2459
Basically they are about the same result as their predecessors.