Resize/Upscale questions

[Selur]

My video file VHS PAL capture to lossless HuffYUV with VirtualDub, 720x576 25i, DAR 4:3, PAR is not set in the header, but I assume it is 1150/1053 as it is from an analog content.

If there's a DAR, there is also a PAR.

Hybrid uses the PAR since it does not change through cropping.

If Hybrid without cropping and resizing properly shows your content without distortions, it will not distort the image unless:
a. you overwrite the Input PAR
b. your disable 'Auto adjust'
so any setting otherwise used will will not distort the image.

It means 720x576 has to be cut to 704?

I would not crop to 704 if that removes active image content.

Do I have to crop frame to 704x576 to get the accurate 4:3 ratio, or 720x576 is the correct value

If the image isn't distorted I would not crop active content.

Is Input PAR correct 12:11?

Why should it?
Assuming your VHS capture wasn't a capture or a mp4 which uses that PAR and you now try to somehow rescue that content ?
There is no way to say that PAR x:y is correct without looking at the content and even then you need something that allows you to properly see distortions,...
(a circle, square or similar)

Is my workflow correct?

the steps you listed look fine, assuming you enabled Blu-ray compatibility in x264 otherwise:

Crop/Resize>Base> LetterBox – checked (Width 1280, Height 720) grayed out, cannot be changed

would not happen automatically.

I was trying to upscale to 1920x1080 following?

Only difference between resizing to 1920x1080 than to 1280x720 would be:
a. a different resize width (height would be auto adjusted)
b. different letterboxing.

The Picture Resize, Target Resolution does not allow to change values to above 984x720.
What do I do wrong?

you probably should also enable: "Crop/Resize->Misc->On Source Change->Maximize letterboxing"
By default Hybrid assumes that if you upscale to be Blu-Ray compatible you want to minimize the letterboxing, thus 1280x720 is the correct solution and 904x720 would be the max resolution which:
a. fits into the letterbox
b. properly displays your content

If you enable "Maximize letterboxing" Hybrid knows you want to go for the maximum available size and thus will aim for 1920x1080 and you are able to use higher resolutions.

Cu Selur