On Mon, 21 Feb 2005, Steven Boswell II wrote:

> >If you have a progressive frame in 4:2:0, then
> >the first chroma line is the average from lines 1
> >and 2.  The second chroma line is the average of
> >3 and 4.

        Right - for 4:2:0.  The "average from lines 1 and 2" and 'lines 3 and
        4' are the ":0" of 4:2:0.  4:1:1 is not subsampled vertically.

> So, if I have a DV file of a 3-2 pulldown of a

        If you have a DV file you have 4:1:1 data and not 4:2:0 so there's
        no chroma line switching needed.

> 24fps source, and I want to convert it back to
> 24fps, I first have to swap lines 2 & 3 of every 4
> lines of the 4:1:1 color, in order to get the
> progressive-frame color to come out right.

        With 4:1:1 all that I think is needed is to undo the 2:3 pulldown to 
        get rid of the repeated fields.  That will give you a 24 (well, 
        24000/1001 ;)) 4:1:1 progressive image.  Then later on when you 
        convert to 4:2:0 y4mscaler will do the right thing with respect to
        the chroma.

> >Of course - but I got a headache the last time I
> >looked at the sources :)
> 
> Eeek...I hope the author responds & gives us an idea
> of how feasible this is.

        It shouldn't be _too_ hard to use the chroma subsampling numbers
        from the stream in place of hardcoded divide by 2 and 4.  Perhaps
        getting yuvkineco handling 4:1:1 data will be sufficient.

        Cheers,
        Steven Schultz



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