[mythtv-users] Daddy, what's a commercial

Dewey Smolka dsmolka at gmail.com
Thu Jan 11 16:24:01 UTC 2007

On 1/11/07, Damian Surr <damian at gingermagic.com> wrote:
>  I'm intrigued by this feature.
>  Currently making a shopping list of things I need to turn my old PC into a
> MythTV media centre, so I've not actually used Myth yet.
>  How does it detect and delete/skip the commercials? Sounds clever. Does it
> work everywhere, or a US thing? (I'm in the UK)

There are a couple of algorithms that can be used separately, or all
of them in combination. There is: Blank Frame detection -- Myth looks
for completely blank frames, which usually come at the beginning and
end of commercial breaks; Scene Change -- Myth looks for drastic
changes in picture composition; Scene Change + Blank Frame; Logo
Detection -- Myth looks for persistent images like on-screen logos,
tickers, scoreboards, etc; and All Methods in combination.

I use Blank Frame Detection in the US, which flags commercials with
around 90-95 percent acuracy. For things like sports the accuracy is
close to 100 percent, while for films with a lot of dark scenes, the
accuracy falls to around 85 percent. I haven't really experimented
with other detection methods which are probably better suited to

I've heard that com flagging is a bit more spotty in the UK, although
I have no direct experience with this.

>  If you wanted to watch live tv, for example a 2 hour film, would you pause
> the start and estimate the time of adverts, then start watching advert free
> 20 minutes later or something?
>  Or don't any of you watch live TV any more?

Com flagging can run concurrent with recording provided your processor
is strong enough to handle both tasks. I have a P4 2.5 GHz which
manages com flagging in real time.

About the only things I ever watch as they're recording are sporting
events, though. For three-hour baseball or US football game, starting
to watch after it's been recording for an hour or 1.5 hours is usually
enough to get through the whole game before catching up with the live

Other than that, I pretty much never watch live tv.

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