[mythtv-users] CBS/NBC 1080i and telecine

Andrew Gallatin gallatin at cs.duke.edu
Thu Jul 16 17:36:35 UTC 2009

Tom Dexter [digitalaudiorock at gmail.com] wrote:
> On Thu, Jul 16, 2009 at 11:54 AM, Andre Newman<mythtv-list at dinkum.org.uk> wrote:
> >
> > On 16 Jul 2009, at 16:02, Tom Dexter wrote:
> >>
> >> longer appears to be the case. ?Maybe over time they'll stop these
> >> various bizarre practices.
> >
> > Please don't complain, this is an example of a broadcaster actually doing
> > the right thing for once!
> > I hadn't thought for a moment that any US broadcaster would be so far
> > thinking to encode in this manner, I'm off right now to try playing some
> > telecine'd CBS shows at 24fps, that 3:2 pulldown drives me nuts. If I'm
> > really lucky I can flip the 3:2 pulldown flags in the transport stream and
> > play the stream at 25fps.
> >
> > Many many thanks for spotting this and pointing it out.
> >
> > Andre
> >
> I wasn't complaining about the change at all...the mixed frame rate
> stuff is one of the bizarre practices I was referring to.  I meant
> that the change could be a sign that they're getting their act
> together.  I really don't understand why they're mixing progressive
> and interlaced frames...that's really odd.

As I understand it, it allows them to get better quality for the
bandwidth they use.  This seems to be done locally by the stations
with the most clue.  Our local CBS affiliate (WRAL) was the first HD
station in the country, and they do it.  The stations with no clue
(PBS, CW) don't do it.  According to somebody on the AVS Forums

  The old Harris Flexicoder that was in use at many many DTV stations
  did not support inverse telecine. So telecine flags are beginning to
  appear more often now as stations upgrade their encoders (and are
  smart enough to enable inverse telecine or more likely lucky enough
  that it's already been enabled in the default configuration from the
  encoder manufacturer).

What's *really* bizarre and uncommon is that our local Fox affiliate
inserts repeat first flags into its HD syndicated reruns at 720p.  I think
they must somehow be doubling the orginal 24pfs to 48fps and then
using repeats to stretch it to 60fps.  Here's mplayer playing a "Two
And 1/2 Men" re-run:

Warning! FPS changed 47.952 -> 59.940  (-11.988010) [7]  %  1.3% 21 0 
A:  24.1 V:  24.1 A-V:  0.009 ct: -0.511 1407/1317 36% 27%  1.3% 21 0 
demux_mpg: 24000/1001fps progressive NTSC content detected, switching framerate.
A:  24.1 V:  24.1 A-V:  0.008 ct: -0.511 1408/1318 36% 27%  1.3% 21 0 
demux_mpg: 30000/1001fps NTSC content detected, switching framerate.
Warning! FPS changed 47.952 -> 59.940  (-11.988010) [7]  %  1.3% 21 0 
A:  24.2 V:  24.2 A-V: -0.027 ct: -0.517 1412/1322 36% 27%  1.3% 21 0 
demux_mpg: 24000/1001fps progressive NTSC content detected, switching framerate.

for a slightly more detailed analysis.

MythTV in the 0.19 / 0.20 range would completely choke on shows like
this.  You'd see surges of fast and slow motion.  I need to see how it
behaves these days.  Apparently, many TV tuners (Vizio) have a problem
with this too.


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