[mythtv-users] Recording from STB that requests channel access pins

[f-myth-users at media.mit.edu]

    > Date: Wed, 13 Jan 2016 10:41:01 -0500
    > From: Eric Sharkey <eric at lisaneric.org>

    > Alternatively, you could have a daemon monitor MythTV's output
    > directory, and analyze all video as it's being written to disk.  Any
    > time it sees a pin entry screen, it sends the code, independent of
    > mythtv.

That sort of thing is essentially what I did for silence/EAS/black-screen
detection.  (Polling the dir for newly-created files was an easy loop,
and if it took non-negligible resources, I'd use inotify or something.)

But be wary of, uh, eccenticities if you're asking by-time for single
frames; mplayer at least seems to occasionally barf in weird ways (not
finding it, or returning something far away in time), requiring some
bombproofing.  Maybe your mplayer is better behaved, or you'll use
something else.