[mythtv] Commercial Detector questions

Paul Andreassen paulx at andreassen.com.au
Sat Dec 10 06:02:52 EST 2005

On Sat, 10 Dec 2005 05:45 am, Chris Pinkham wrote:
> >  - Australia doesn't have blanks between ads so changed MAX_COMM_LENGTH
> > to match MAX_COMM_BREAK_LENGTH (is this the right thing to do?)
> I think that would accomplish what you want yes.  In SVN, you could use
> the undocumented 'CommDetectMaxCommLength' setting in the DB.

Will this ever be a mythtv-setup option, instead of undocumented?  Or better 
yet autodetected.

> >  - Patches to match my global record before of 5 minutes and after 10
> > minutes - Pick format from 5 minutes to last 10 minutes
> > 	- Move Logo detecting 6 minutes in and if not detected try in 15 minutes
> > in (it maybe more sensible to reduce my before time to 1 minutes)
> With current SVN, we now have the ability to know the program's scheduled
> start and end times in addition to the actual recording's start and end
> times. I think that post-0.19, we could make mythcommflag look inside the
> scheduled timeperiod for the format and logo and not at the actual
> recording start since we may have started recording early.  I made a note
> on my TODO to look into this unless you want to take a look at it.

See attached commflag-svn_start_stop_times.patch.  This patch hasn't been 
compiled so probably has bugs. I'm not sure that the macro MAX is acceptable 
MythTV coding style.      

> The 6 vs 15 minute thing would have to be able to handle in-progress
> recordings also, so it wouldn't try them unless we were far enough behind.
> For in-progress recordings, we could delay until requiredHeadStart seconds
> past the actual program's scheduled start time to handle the logo
> detection.

I've dropped the second attempt at logo detection because during testing it 
wasn't any more successful.  It was actual worse on my test video.  Even a 
third test was useless.

> > Does it make sense to +10 score when format matches?  My understanding is
> > format matches mean either show or ad.  And format non matches mean ad.
> For this, are you thinking take out the +10 when formatMatch >
> (fbp->frames * .90) and leave in the -10 when formatMatch <
> (fbp->frames * .10)?
> Your logic makes sense, we are more sure that something is not part of the
> show if it's format does not match the show so we can -10 there, but
> we aren't as sure what it is if the format does match so why +10 in that
> case.  I made a note about this also.

See attached commflag-svn_format-aspect.patch.  This patch hasn't been 
compiled so probably has bugs.  I did test this on 18.1 and it works much 
better for my recordings.  Aspect changes untested because I don't have them.  
The difference in score due to frame block size is because the larger blocks 
are more meaningful for this test.  Are they?

> Just to give you an idea of what other things I may be looking into
> shortly, here are a few things from my TODO:
> * Keep track of min/max brightness found during logo detection so we can
>   use that information later to determine what is really a blank screen and
>   what is not.  (ie, if the min is only 50, we might want to try to
>   compensate in some of our other thresholds)
> * Fade detection, checking the last X number of frames to see if the
>   brightness is constantly increasing or decreasing.
> * Better logo detection.  I looked into this for a while but haven't messed
>   with that code at all recently.  Detecting the logo is easy using
> something like sobeil, checking for the logo in each frame after you've
> found what the logo looks like that is the part that is a bit harder since
> we're dealing with video.

I did some basic image processing a uni but nothing like this.  Its hard for 
me to write code for svn when I'm using 18.1.

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