[MEncoder-users] How does one interlace progressive content?

[Grozdan Nikolov]

On Sunday 05 August 2007 02:45, Loren Merritt wrote:
> On Sat, 4 Aug 2007, Grozdan Nikolov wrote:
> > I have a 25fps progressive PAL DVD and I want to make it interlaced
> > during encoding. Do I have to only add the tinterlace=4 filter to the
> > filter chain or do I also have to provide a -ofps value?
>
> tinterlace=4 will give you 12.5fps interlaced output. That can't possibly
> look better than 25fps progressive even on interlaced displays.

so how are interlaced PAL DVDs made? I have a couple of them here and mplayer 
always reports 25fps frame rate

I did a small test here with tinterlace=4 on a 25fps progressive PAL DVD and 
during encoding, mencoder printed a lot of duplicate frames but the result 
was a 25fps file (or at least that's what mplayer and avidump reports). The 
file played just fine without sync issues and I could see the interlacing

>
> While it's technically possible to write a full-framerate interlacer, I
> don't remember ever hearing of it being done. The method would be: apply a
> motion-compensating temporal interpolation algorithm to double framerate
> (which does not exist in mplayer), then apply tinterlace.
>
> > Also, is the above procedure the same if you want to interlace a
> > 23.976fps progressive NTSC content?
>
> Don't change the video at all, just set the repeat-field flags when
> muxing. This of course does not result in interlaced video, it results in
> telecined video. But it's the algorithm used to put any film on dvd.
>
> > what about 29.97fps progressive content?
>
> Same as 25p.
>
> --Loren Merritt
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