[FFmpeg-user] Command line option to convert to square pixels?

[Dan Flett]

> On Nov 18, 2011, at 18:06 , Jamie Tufnell wrote:
> 
> > How can I convert to square pixels IF necessary, AND 
> maintain height 
> > based the input file's display aspect ratio?
> > 
> > I want to force the width of the output file, but set 
> height based on 
> > the input file's display aspect ratio and convert to square 
> pixels if 
> > necessary.
> > 
> > Right now I use -vf "scale=640:-1" and I want to extend that to 
> > convert to square pixels as well.
> > 
> > e.g. the same command line option would have the following effects:
> > 
> > (no square pixel conversion necessary)
> > in: 1440x810 PAR 1:1 DAR 16:9   => out: 640x360 PAR 1:1 DAR 16:9
> > in: 1440x1080 PAR 1:1 DAR 4:3   => out: 640x480 PAR 1:1 DAR 4:3
> > 
> > (convert to square pixels)
> > in: 1440x1080 PAR 4:3 DAR 16:9  => out: 640x360 PAR 1:1 DAR 16:9
> > 
> > Is there a way to do this?
> > 
> 
> have you tried using an expression in the scale filter that 
> uses the sar constant (http://ffmpeg.org/ffmpeg.html#scale) 
> to compute width correctly and then use the setsar filter 
> with a value of 1:1 to force square pixels? 
> 
> I would guess that should do the job.

When doing any sort of scaling, the first thing in my -vf sequence is this:

-vf scale=iw*sar:ih

This scales the width to make square pixels.  Any subsequent transformations
are then done on square pixel video.