[MPlayer-dev-eng] Re: [PATCH] further dvr-ms playback improvements

[Trent Piepho]

On Fri, 3 Nov 2006 sci-fi at hush.ai wrote:
> On 2006-11-02 04:48:03 -0600, Trent Piepho <xyzzy at speakeasy.org> said:
> > On Wed, 1 Nov 2006 sci-fi at hush.ai wrote:
> >> On 2006-11-01 06:05:38 -0600, Trent Piepho <xyzzy at speakeasy.org> said:
> >>> On Wed, 1 Nov 2006, Nico Sabbi wrote:
> >>>> the frame time doesn't depend on the progressiveness/interlacing
> >>>> of the video, but on the framerate. For some time now, for some obscure
> >>>> reason,
> >>>> many american broadcasters have been transmitting ntsc content
> >>>> tricked (changing the repeat-* in the sequence headers) so as to make
> >>>> the video stream look like encoded ad double the framerate.
> >>>
> >>> Broadcasters stick with one resolution/framerate all the time.  They don't
> >>> switch back and forth from commercials to programs, video source to film
> >>> source, native HD to up-convert, and so on.
> >>
> >> etc. as you say.  Several series are sourced from videotape
> >> at 30fps (let's forget fractions eh? ;) ), so when a
> >> commercial comes on that's shot on film, we see it switch to
> >> 24fps.  And vice-versa when the show is film and a
> >> commercial is on tape.
> >
> > Do you have a sample ATSC recording that switches framerate?
>
> As I said, I have hundreds ;) ... I think I found a good
> sample to put up, let me double-check with you to see if
> this is what we're talking about here:-
> I see a lot of these messages on the mplayer console while
> it plays most D-SDTV firewire recordings:
> DECVIDEO:
> demux_mpg: 24000/1001fps progressive NTSC content detected, switching
> framerate.

That's what I suspected.  That isn't changing framerates.  The broadcaster
is just turning soft-telecining on and off.

This is exactly what Nico said some broadcasters are doing for an "unknown
reason".  They insert repeat-field codes or encode duplicate frames to
convert their input material at say 30 or 24 frames/sec into their
(non-changing) output rate of say 30 or 60 frames/sec.  Everyone knows why
they do this to convert 24 frames/sec into 30 frames/sec interlaced on
DVDs.  The reason this is done to convert 30 frames/sec into 60, is that
the ATSC broadcast standard getting used is 60 frames/sec, and so that's
what must be output.

> Being nitpicky, this isn't from ATSC ("over the air"), but
> QAM (digital cable/satellite).  Signal format shouldn't

To be nitpicky, satellite doesn't use QAM, but QPSK.  The new DVB-S2
standard also supports BPSK, 8-PSK, 16-APSK, 32-APSK.