[mythtv] commdetector2

Robert Tsai mythtv at tsaiberspace.net
Sat Sep 2 05:35:11 UTC 2006

On Sat, Sep 02, 2006 at 12:59:17AM -0400, Daniel Walton wrote:
> > > - Blank frames are marked pretty reliably for digitial
> > > recordings but for analog where the blank frames aren't as dark
> > > (sometimes in digitial they are 100% black) I saw a lot of
> > > misses.  Right now a MAXRANGE of 32 seems to do the trick but I
> > > am reflagging everything to make sure I'm not getting any
> > > non-blanks flagged as blanks with this setting.
> >
> > The trade-off of a bigger range is that other
> > monochromatically-colored frames (say, a grey-out scene like in a
> > snowstorm or something) might be mistakenly identified as "blanK"
> > frames.
> How difficult would it be for the commdetector to distinguish a
> blank white or grey screen vs a blank black screens?  The higher
> maxrange value is very much needed for analog recordings.

Probably not hard. You basically want to also add a maximum value, in
addition to some range.

The range is also used to detect aspect ratio changes. The
letterboxing/pillarboxing is sometimes black, sometimes grey, etc.

> > The trade-off with aggressively increasing this value (e.g., go as
> > far back as necessary to find a blank frame) is that if a
> > commercial break is actually *not* delimited by blank frames
> > (e.g., broadcast resumes immediately after commercial with no
> > blank frames), then you might pick up an inter-commercial blank
> > frame as the resumption of your regularly-scheduled show.
> I have a recording of a show on FX with the following timeline:
> 0:14:17 logo disappears
> 0:14:18 first blank screen of the commercial break
> 0:17:19 last blank screen of the commercial break
> 0:21:47 logo re-appears
> This currently gets flagged as a commercial from 0:14:17 to 0:21:47
> (4 1/2 minutes too long) because the station waited longer than my
> 35 second MAXBLANKADJUSTMENT setting to show the logo after coming
> back from the commercial break.  If the code did "go as far back as
> necessary to find a blank frame" then it would fix the flagging for
> this scenario but I follow what you are saying about the case where
> there is no blank frame when the show resumes. How you set this just
> depends on how you want the flagger to act when it isn't 100% sure.
> I'd prefer that it not flag any of the show as commercials and if it
> misses flagging some commercials then I can skip over those parts
> manually.

I am hoping that audio analysis can handle these kinds of cases.


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