h264 Cap at ~2 threads for encoding?

[Mitch Capper <mitch.capper@…>]

After setting HTTPLiveStreamThreads to 16 and seeing mythtranscode say its encoding with 16 threads (rather than the default 2) the CPU usage only went from 170%->220% (despite plenty of additional free cpus). I do see a hardcoded c->slices = 8; in avformatwriter.cpp for h264, which sets the picture subdivisions im not sure if that is too low for more threads or its something else.

If anyone has any initial thoughts or suggestions I am open to it, otherwise I will start tweaking settings to see if we can allow for more threads.

There is such reference to a cap from about 4 years ago: ​http://www.gossamer-threads.com/lists/mythtv/users/531170#531170