[mythtv] New Method for Commercial Detection.

Steven Adeff adeffs.mythtv at gmail.com
Tue May 2 18:22:22 UTC 2006

On 5/2/06, Robert Dunn <anakinberrybread at paradise.net.nz> wrote:
> Lucas Meijer wrote:
> >   if I don't record anything for two weeks,
> > chances are good all the known commercials have stopped airing, making
> > the system unable to "relearn" the
> > new commercials..
> >
> One possible way to reduce this is to run the commercial detection all
> the time, if the PVR is switched on and tuned to a channel.

When LiveTV exits Myth no longer listens to the tuner, recording has

> > One quickly goes to think of an online database of known commercials
> > (probably region specific), but that
> > off course would have problems of its own: (deliberate) corruption of
> > the database with incorrect fingerprints,
> > being the first one that comes to mind.
> >
> This isn't as much of a problem as you would imagine, the reason this
> technique can work is because commercials repeat, where as programs do
> not. Even if someone were to submit keys for the latest episode of a TV
> Show. They wouldn't detect the program unless it aired again before the
> keys 'timed out' and were removed from the database. Over here there are
> very few TV shows which would have the same episode aired within a
> couple of weeks of each other.
> >think that
> >this method would have to be used in conjunction with other methods to
> >determine where the blocks start and end, otherwise it could be very
> >cpu intensive to analyze a whole hour long show second by second looking
> >for signatures that match the known lists.  In your testing, how have you
> >handled this kind of situtation or have you just done analysis to compare
> >two clips to see if they contained the same audio.  Another thing that
> >will complicate this is the fact that analog broadcasts will not be
> >identical every time, so you wouldn't always get a 100% match as you
> >with an exact digital copy.
> In my embedded DSP device, I could generate keys and check a smallish
> database of keys (with no search optimizations at all) in real time. The
> time consuming thing is the checking of a database. The goal for my
> I mentioned is to achieve commercial detection in real time, which
> on the number of keys needed I think should be achievable. I dont know
> about MythTV (im slowly learning) but is the commercial flagging done in
>real-time or as a post processing effect?

It is an option configurable by the user. It can be set to start while
recording (I believe the delay is somewhere around 10seconds behind "now"
currently). I personally don't real-time because I don't have the processor
speed to commflag the number of HD streams I can record in real-time and my
recordings drive is not fast enough to handle that many read and write

> This method relies on spectral components of the audio, and is highly
> robust (to quote the research paper) to noise so I dont imagine the analog

> broadcast would be a problem.

I wonder if Philips will integrate this into their recent patent to further
prevent us from skipping commercials...

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