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

[Trent Piepho]

On Wed, 1 Nov 2006, Nico Sabbi wrote:
> > the file in question the average frame time was set to 0.0166833 in
>
> 59.94 fps
>
> > what I think is a PAL format HD recording. That value is half the
> > frametime of what an NTSC frame should be so maybe the recording was
> > actually NTSC progressive scan but I dont know. And I dont know what
> > the average frame time should be for progressive scan - presumably it
> > is half??? I need more samples where I can be sure of the source).
>
> 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.

One of the ATSC standards they have to choose from is 1280x720 at
60000/1001 _frames_ per second.  Yes, frames, not fields.  Yes, that is
double the NTSC frame rate (and it's not interlaced either).

> The decoder will have to deal with this change somehow in order it to show
> it correctly on tv (that accepts 59.94 _fields_ per second, not _frames_
> per

For an old standard definition TV.  North American digital broadcasts are
designed for high definition TVs, which can display 59.94 frames per
second.

> second as  indicated by the sequence headers), and repeat the other field
> when indicated in the stream, so what's the benefit of this abomination
> is really beyond my understanding.

The benfit is that the transmission is the proper standard.  It the same
reason NTSC DVDs don't use a 24 fps frame rate, but use 30 fps and
soft-telecining.  Same reason PAL DVDs don't use 24 fps either.  The
standards say DVDs are 30000/1001 fps for NTSC and 25 for PAL.  So if you
have 24 fps film, it needs to get converted.