[mythtv] (How) does allow re-record work?

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

    > Date: Wed, 25 Jul 2007 02:16:42 -0400 (EDT)
    > From: f-myth-users at media.mit.edu

	> > Date: Tue, 24 Jul 2007 21:57:38 -0400
	> > From: Tony Lill <ajlill at ajlc.waterloo.on.ca>

	> > I was thinking progamatically. I've modified the commercial flagger to
	> > recognize recordings with long blank stretches (tested and working) or
	> > long frozen stretches and do "something". Just working on the
	> > something bit.

    > Can you post your patches?

Here's another thing that such analysis might catch & would be good to
add, but I'd need some advice on how to do so (and seeing your patches
might help a bit w/the video side):

I frequently have recordings in the midnight-6am range trashed by the
local cable co inserting 30-60 second "mandatory weekly test" messages
in place of whatever they're ostensibly transmitting.  They seem to
pick a random channel up in the Discovery/TLC/Bravo/SciFi/etc ranges
and a random time, so it's not as if I can just avoid recording a
particular channel in a particular timeslot.

And since the interruptions are brief and randomly-distributed, there's
no feasible way right now to avoid them besides watching everything---
even though repeats of things aired then are common (also at times that
might be vulnerable) and a repeat could be automatically snagged if some
automation can detect the insertion.  [Whereas, by the time someone can
watch one the next day, the damage is done and the repeat has aired.
Yet it's infeasible to rerecord -everything- that was recorded during
25% of the day just to recover from one insertion/week...]

The inserted tests are typically static white text on a red background
and have distinctive modem tones at the start and end, no doubt to
alert automated equipment if the test was instead a real emergency
broadcast.  (I -think- they might do similar things with Amber Alerts,
but I've only seen one of those and probably no longer have the bits
to check.)

I'm thinking that something which was scanning the audio track could
presumably detect those tones and flag the recording, but (a) I don't
know what exactly those tones are (presumably somebody can point me at
the standard describing this?) and then I'm not sure what tool might
be most-easily run on an audio stream to pick out just those tones.
(Bonus would be if those tones were unique enough that, e.g., random
modem noises in a movie wouldn't false-trigger; of course, checking
for static video content at the same time would be pretty definitive,
but much more complicated.)

Any ideas?