[mythtv-users] Skipping adverts in UK using DVB-T - supported ?

[Tom Hughes]

In message <200501192307.j0JN7Wcd007133 at panther.bc2va.org>
          "Chris Pinkham" <cpinkham at bc2va.org> wrote:

> > Haven't updated my cvs version yet to try the new detection, but does
> > it also monitor for aspect ratio changes?  Just noticed while watching
> > tv yesterday quite a few channels change aspect ratio when they switch
> > to the adverts (I'm in the UK).
> > 
> > In this situation it could be a very accurate way for detecting ads.
> 
> Is this a physical aspect ratio change or does the frame stay the same
> ratio and have black bars on the top/bottom?  I have a sample of a UK
> broadcast that uses the black bars and will be trying to code up something
> to detect that transition so it can be used to determine where commercials
> start/stop.  If you mean a physical frame aspect ratio change, then I'd
> like to detect this at some point but don't have any sample recordings
> to test with right now (I'm in the U.S. with analog cable).

Well it would be black bars on the side of the program if anything
rather than black bars on the top and bottom of the adverts.

In a DVB-T stream there are two ways of handling aspect ratios. For
simple 4:3 vs 16:9 it can be done with a simple flag. In that case
then the transmitted data is always the full picture area and the
flag tells the receiver what aspect ratio to use when displaying
the data - the resolution doesn't change, so would be 720x576 or
704x576 in the UK depending on the channel.

The other option is to use an AFD where a 16:9 picture is transmitted
and if the content is 4:3 then there are black bars on each side. There
is then an Active Format Descriptor (AFD) which indicates which part
of the transmitted picture to display. That allows more choice of
ratios but in the UK at least only 4:3 and 16:9 are used.

Some channels use AFDs in the UK and some use the simple flag. Most
of the AFD channels don't have adverts however, but I think there is
one that does - certainly Five was, but it may have changed recently.

I'm not sure how Myth handles those two cases however, or what you
see in the stream when you read it back from disk.

Tom

-- 
Tom Hughes (tom at compton.nu)
http://www.compton.nu/