[FFmpeg-user] Crop, Scale, Pad without distortion

[Hans Carlson]

On Mon, 27 Jan 2020, Devin Heitmueller wrote:

> FWIW, I've done a bunch of aspect ratio conversion based on AFD (including
> cropping out letterbox/pillarbars and dealing with nonsquare pixels), and
> I've had the best success with crop->pad->scale.  There is also at least
> one bug in the scale filter where it doesn't properly handle upstream
> filters changing the properties of the the scaler input link, which causes
> incorrect scaling.
>
> I've got a tree which addresses those issues.  Let me know if you want a
> link.

I would a love a link.  Any good examples might help me understand better. 
Thanks.

> Almost all of those issues come down to sar/dar problems, so you should
> turn up the logging and look at the sar for each link in the filter graph
> to debug.

Yes, I'm sure that's my problem... I just don't have a good enough 
understand to figure out what sar/dar need to be and where/how they 
should be used.  Any help is appreciated.