AW: [mythtv-users] Automatic Commercial Detection - how to get it

Flo Kohlert flokohlert at muenchen-mail.de
Fri Sep 24 17:03:28 EDT 2004


>I've yet to look at the audio data enough to know this or not, but I've
heard
>and read that it's not volume, it's something else that changes that makes
>it seem louder.  I don't know.  I haven't even delved into trying to
process
>the audio to detect commercials, that's a whole 'nother beast.  Things like
>audio silence during blank-frames and such would really help proper
>detection.
>
>--
>
>Chris

I'm not a coder by any stretch of the imagination, but if you like I'll see 
if I can pull apart a few MPEG's and have a look at the waveforms and 
suchlike and see if I can figure out what's going on.

As I don't know how Myth works (i.e. how it would "see" the audio if and 
when it scanned it - I'm imagining just as a regular waveform), if anyone 
could proffer an idea for the best way for a patch that looked at the audio 
would work, I'd be much obliged. Also, if there's any audio manipulation 
done by either Myth's software encoding or by the ivtv-range that anyone 
knows about I imagine it would prove very helpful. In the meantime I'll 
check out some of the other links posted above.

Bear in mind I've only got access to the UK's terrestrial channels, so if 
there's any major differences between these and your NTSC streams I imagine 
I'll be up shit creek ;) 

It´s not louder at least not here in germany, working for a tv-production
company i can safely say that the channels tolerance against high peaks are
somewhat more tolerant regarding commercials but not significant as all of
the program runs through limiters before getting on your tv. So they´ll
allow peaks of +2db sometimes on ads they might reject on normal programs,
but you would barely notice this. 

The biggest difference is that you got nearly no dynamics on ads as they are
heavily gated and then compressed, which makes it feel louder (no quiet
moments). A thing you´d never do on movies/series as you´d kill a
possibility to create suspense.

So you could use this for detection but it would probably fail on nearly any
musicvideo and many heavy action passages.

flo



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