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In <1992Sep03.042045.5095@ecst.csuchico.edu> rmintz@ecst.csuchico.edu (Rich Mintz) writes:

>I'm interested in building a device (or making my 386sx 
>act like one) that will be able to distinguish television 
>commercials from television programs. I've talked to a 
>few people and have heard of a couple of ways it is said 
>that this can be done.
> 
>First, I was told that the audio during commercial 
>announcements on tv is boosted higher than that used for 
>normal programs (for obvious reasons). However, I've 
>tried all kinds of analysis with volume levels, averages 
>over specific periods of time, etc, using my computer's 
>sound card (with stereo capability), with no luck at 
>finding any dependable pattern to distinguish    ads from 
>shows.
> 
This idea has been around for some time, unfortuantely as you have
discovered the levels arent really changed. However from having the
TV on in the background adverts do sound louder. I can only imagine that
they are compressed (an audio technique which compresses dymanic range)
more heavily to make you notice them (drums etc seem to be higher in the
sound mix). IF this is so it may be possible to try and discrimate on this
basis, although I havent got a clue how.

>Someone else told me they had heard that what I'm wanting 
>can be acomplished by analyzing the video transmission 
>for the presence of computer-encoded information that 
>accompanies programs, but not commercials. I assume he 
>was referring to Closed-Captioned (CC) text sent along 
>with many shows for the benefit of the deaf who have 
>special receivers for these signals.
> 
In the UK Tv signals are sent with quite a bit of information. Firstly there
is Teletext, a viewdata system (which includes the CC text); timing markers
for opt-out stations to que to (these are in other spare lines but I dont
know where) and most importantly the little funny square. On our commerical
stations two queue markers are sent at the right hand edge of the screen in
the top 20 or so lines, these look to be some sort of tone which masks the
signal underneath. The tv companies use these to que in local adverts in
networked programmes. I think the first marker appears 30seconds before the
adverts. So you could build a box to look for this and once its found it
wait 30secs and kill the audio. However I dont know if this is present
in US systems.

>Any suggestions? Thanks.
> 
>   Rich -> rmintz@cscihp.ecst.csuchico.edu

Raggy

-- 
Raggy                 | God smiles upon the little children, the alcoholics, and
u9dmlb@ohm.york.ac.uk | the permanantly stoned. S.King.