File conversion requires some settings that seem odd

[TVBroadcastAudio]

Hello,

I'm attempting to convert old SD 4x3 video into QT H264 files. Due to the capture device they're captured as 16x9 HD H264 files and then converted to 4x3 SD files. Using VLC to do the conversion I must enter some odd values to get the desired resolution and aspect ratio, and the resulting QT Info window shows some things I don't understand. I'm hoping someone here can shed some understanding.

Capture -
- MacOS 10.14.6.
- BlackMagic H264 Recorder, HDMI input.
- Playback = VHS with HDMI output - always outputs 16x9 HD stretched.
- Resulting files = H264/AAC, 8Mb/s, 1920x1080 5994p.

Conversion to 4x3 -
- MacOS 11.6.4 for test purposes.
- VLC v3.0.16
- Desired files - H264/AAC, 3Mb/s, 640x480, 5994p, 4x3

The issues -
- In the video conversion settings, entering 640x480 as the desired resolution results in a 480x480 file and visually it's obviously square and not 4x3.
- Entering horizontal resolution values above 640 result in an increasing resulting file resolution.
- To achieve a final resolution approximating 640x480 requires entering a horizontal value of 740 pixels resulting in a horizontal resolution of 641.
- The file has the correct 4x3 aspect ratio is listed as 641x480, and looks correct.

This may be an oddity I can work with except that the Info window in QT seems to know something is off -
- it displays a "pixel aspect 629:726" data field that doesn't exist on the original HD file.
- the Resolution field says "740x480 (641x480)"
- Multiplying the entered 740 value by the "pixel aspect" value of 629/726 results in 641, the resulting resolution, so the math adds up.

Therefore something is being conveyed that I don't understand.

I've included links to three screenshots -
- VLC video conversion settings needed to generate a file approximately 641x480 4x3 SD.
https://www.dropbox.com/s/m72stk5lp63p5 ... s.png?dl=0

- The QT Info window for the original HD file.
https://www.dropbox.com/s/ww10z2xlfay3l ... o.png?dl=0

- The QT Info window for the converted file illustrating the odd data entries.
https://www.dropbox.com/s/0miknhj6e7lqy ... o.png?dl=0

Could someone shed some light?
Is it normal when changing aspect ratio to have the pixel aspect ratio change?
Is there a way to not do that?
Is the file actually 740h and the display device is scaling to it's native pixel aspect resulting in an apparent 641h?
Will this odd pixel aspect ratio scaling cause problems on certain devices?

Thanks,
TVBA