The ffmpeg process will use all available CPU usage to transcode as quick as possible, unless you have throttling enabled.
My Emby Server PC is a Quad-Core Q6600 2.4Ghz with 8Gb ram and I don't have any issues transcoding to my Now TV and Roku boxes. Slight issues with 1080p videos transcoding to Nexus Player and Amazon Fire TV.
Maybe, but in my case, it seems to use all available CPU for the most part, and cause the playback to be VERY inconsistent (pausing/buffering nearly constantly, to the point that it's entirely unwatchable, even on the very low resolution settings).
However, loaded up process lasso and took a look.
It looks like the MediaBrowser Server app, AND ffmpeg are being ran at the "below normal" CPU priority. Using ProcessLasso to FORCE this to "Normal" looks to have completely fixed the issue for me.
I'm not sure why it would be set to below normal, but it's clearly impacting performance of the server.
I'm not sure what I can post to help identify the issue in my case, but I'm more than willing to grab anything from the system, or even let a dev take a hands on look at my system.
Because installing and configuration Process Lasso is a hack. The issue needs to be fixed in the code.
So anyone else still having this issue, I'd recommend try to see if Process Lasso (or similar) fixes this issue for you.
Also, a suggestion, could you limit the number of threads that ffmpeg uses, instead of defaulting to "0" (all). This would help prevent it from eating all available CPU power.