[mythtv-users] Refresh Rate reported for interlaced output (was: New nVidia 169.07 and interlace changes)

[Tom Dexter]

On Dec 21, 2007 11:52 AM, Tom Dexter <digitalaudiorock at gmail.com> wrote:
> On Dec 21, 2007 10:37 AM, Michael T. Dean <mtdean at thirdcontact.com> wrote:
> > On 12/21/2007 10:26 AM, Tom Dexter wrote:
> > > Speaking of that patch, I'd still love to know why the frontend
> > > reports 60Hz output as 30Hz when the output is interlaced....which is
> > > what that patch changes.  I posted a question to the dev list about it
> > > some time ago and got no response:
> > >
> > > http://www.gossamer-threads.com/lists/mythtv/dev/302387
> > >
> >
> > 1080i60 is 1920x1080 pixel frames shown at 30 frames per second.  Each
> > frame is composed of 2 fields--each having half the number of lines of a
> > frame.
> >
> > 720p60 is 1280x720 pixel frames shown at 60 frames per second.
> >
> > There is no such thing as 1080i120 or 1080p60 in the ATSC
> > specification.  There is, however, 1080p30 and 1080p24, as well as
> > 720p30 and 720p24.
> >
> > http://www.hdtvprimer.com/ISSUES/what_is_ATSC.html
> >
> > Mike
> >
>
> Maybe I'm missing something...you're talking about frame rates
> correct?  I was talking about the refresh rate.
>
> The frontend reports a frame rate of 30 for 1080i60, which is correct,
> and the patch we were referring to doesn't change that.  However it
> also reports a refresh rate of 30 rather than 60.  Isn't supposed to
> be 60, as in the 60 fields per second?
>
> In any case, that reported refresh rate causes the frontend to
> disallow bob de-interlacing when running at 1080i, which works
> perfectly otherwise, and produces the best display of 1080i content I
> can get by far.  Seth will concur.
>
> Tom
>

Does anyone have any insight on this one...this still has me really perplexed.

Michaels response above is a bit like the response that was posted to
Viktor's bug 2903 (with the patch) where it was pointed out that a
50Hz interlaced display only has a 25Hz frame rate, when the frame
rate being reported isn't what's being questioned at all, but rather
the refresh rate.  The two values are stored separately in the
frontend, and the frame rates for 60Hz and 50Hz displays are in fact
stored as 30 and 25 respectively, but the refresh rates are also 30
and 25 rather than 60 and 50.

I understand that 60Hz interlaced displays have a frame rate of 30,
but do they not have a refresh rate of 60 rather than the 30 reported?

What's even more confusing is the fact that bob deinterlacing appears
to work with the patch and in fact looks great for those of us using
it with interlaced displays.  Everything I read about bob indicates
that is relies on doubling the frame rate, which certainly doesn't
sound like something that would work with 30 frame per second video on
an interlaced display.  I'd imagine that's probably what the reply to
bug 2903 was driving at.  I'm not sure what actually ends up happening
at the display for those of us doing this, but it certainly looks
great.

Tom