OK quick update. Changed the Min.Bitrate to 10,000,000 Bit/s (same as 10Mbit/s) and altered Max resolution as directed. Left everything else alone. Immediately got 1080p streams! Yay! So that worked. Quality is vastly improved as well. Less block noise and banding.
Next I upped the Min.Bitrate to 20,000,000 (same as 20Mbit/s) just to see if it would choke or stutter (I have 1Gbit/s Internet so 20Mbit/s shouldn’t stutter due to that being a bottleneck). Works good so far. Can’t say the quality is noticeably better than 10Mbit/s but I haven’t watched that many videos yet. Could be the limiting factor is the source material, I dunno.
Sam, as you can see above I got 1080p streams working. I know the YouTube add-on isn’t your product. However, is there a way to have OSMC automatically set InputStream Adaptive to max resolution and/or higher bitrates? I guess the ideal thing would be to ship OSMC with the YouTube add-on already installed and configured but you may not be able to do that due to license restrictions.