I have been able to get my Harmony working with Channels via the Nvidia Shield thanks to the various forums posts and guides found on here (see another post I made explaining which profile I'm using: Harmony hub and windows profile pairing problem)
However, I haven't been able to figure out how to map the record button on the remote to something Channels recognises.
I thought Button Mapper would be the solution, but perhaps I've not configured it correctly because it hasn't worked. Was the following correct?
- Mapped F5 to Record
- Opened Button Mapper on my Shield Android TV
- Press "Add Buttons" and the same again
- Pressed my Record button, which detected it as F5.
- Selected the F5 mapping and pressed "No thanks" to "Pro Features"
- Pressed "Single tap"
- From the drop-down menu I chose "Media" and then selected "Record".
- Pressed Back, Back, and then Exit.
- Launched Channels and went to Guide. Pressed the Record button but nothing happened.
To confirm, I've enabled Button Mapper in the Android TV Settings -> Device Preferences -> Accessibility -> Services -> Button Mapper.
Another option according to this guide (https://getchannels.com/docs/apps/remote-control/advanced/#remote-shortcuts), is to add a Windows Computer device to your hub and add it to your Shield Activity as an extra device. The trouble is, when I mapped "Record" from that device to a button on my Harmony, the remote screen said "You have to use the Harmony App to pair this device". As my Shield is already paired within the Activity, I can't see any way to pair another device, so got no further there?
If someone could help me figure this out please, I will definitely be a subscriber. I'm within the 30 day trial atm and have to make this wife friendly, so the Record button is my final obstacle. 
Thanks in advance!