[Cin] Anamorphic 16:9 SD-DV(D) widescreen to AV1.webm

[Andrea paz]

A convenience when doing these tests is to apply the "Downsample"
filter to the timeline track and set it, in H and W, to at least the
value 40. This will immediately show whether the pixel shape is square
or rectangular, and, in the latter case, whether it is stretched
vertically or horizontally.
There is also to mention the "Auto aspect ratio" option in Set Format.
It always returns the pixel (PAR) to the square shape by changing the
DAR. If you leave the Auto checked box, every time we make a change it
is reset to the square pixel. Auto, however, turns off if you set one
of the presets and you have to re-enable it manually.
Crop or sometimes pad (letterbox) is unavoidable when we impose a
different aspect ratio from the starting one.
I'm running tests with Terje's sample (thanks!) and getting the same
results as him. I honestly don't understand the difference in
rendering between CinGG and ffmpeg. In Cingg the initial SAR (actually
the PAR) goes from 4:3 (=1.333) to 64:45 (=1.422). However, 1,422 is
the correct value (for CinGG), to see Raffaella Traniello's guide:
http://www.g-raffa.eu/Cinelerra/HOWTO/anamorphic.html

I still have to make a new build with Andrew's last 2 patches (for DV
16:9) to see if anything changes.