Recording has been .TS format, and sometimes worked.
I've uninstalled 23, re-installed 22, tested, then uninstalled 22 and re-installed 23. I also removed my Ceton InfiniTV, updated the drivers and firmware in my HD HomeRun, and tested TV again in MC.
Getting similarly unusable results was discouraging after all that.
So, I tried some other troubleshooting: and when I switched from Red October HQ (that I've been using for a long time without issues) to Red October Standard, TV worked again. Of course, watching my 3D Blu-Ray MKVs doesn't work when I do that workaround for this new problem, so I'll have to switch my viewing "mode" back-and-forth for different kinds of content until this functionality is restored. But this is a work-around I can control, so I'll deal with it this way for awhile.
Thanks for the ideas and assistance.