When watching live TV in MythTV, press R to start recording. Now, I have yet to find a simple hotkey to stop the recording right then and there – pressing R again does stop it, but it also deletes the recording (or cancels
it).
To stop the recording, you first need to exit the watching mode by pressing Esc. Next, from the main menu, go to Manage Recordings and then Upcoming Recordings. From the list available there you can then select the program currently being recorded with the up and down arrows. When selected, pressing Enter finally gives you the choice of stopping the recording (again, selectable with up and down arrows and the Enter key).
When I began to look for the solution for this problem, I was amazed (and truth be told, extremely frustrated as well) that Google didn’t have a direct answer to what seemed to me to be a pretty obvious question. However, it looks like the operating logic behind MythTV is based heavily on using program guides and scheduling instead of on what is perhaps a little old-fashioned way, controlling the start and stop of recording manually.