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

[Loren Merritt]

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.

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