I know I sound like a pedant but so many of these old TV recordings are uploaded this way on youtube. I was so annoyed by this infact that a few years ago I made a dumb extension that squeezes the video element back to 4:3 [1]. I'm not sure if this still works though.
[1] https://chromewebstore.google.com/detail/doddimnledmldclhlbf...
And here's the clip with aspect ratio corrected: https://www.stretch.site/?videoUrl=https%3A%2F%2Fwww.youtube...
It cares about overall pixel size, and for example standard 720x576 standard def 4:3 video will be brutally compressed compared to the exact same video upscaled using any non-AI upscaler (even nearest-neighbour) to 1440x1080.
I dug into this a bit a while ago, and could probably post my finding here if anyone was interested.
As an uploader you should never add black bars (if they are in the source, crop them out before uploading) and of course never distort the video. This ensures the best playback experience for all devices.
In an ideal world yes. In practice, the YouTube layout looks weird on aspect ratios that aren't 4:3 or 16:9. If you upload any vertical video it gets categorized as a short, so that's out of the window - and even for things like 21:9 you get a teeny tiny player on desktop since it just fits the width.
Quick googling suggested that square video under 3 minutes will be automatically classed as "shorts", which much of HN hates and may never have seen.
Wes Anderson's "The Grand Budapest Hotel" has every section of the movie shot in the time appropriate aspect ratio.
If you buy the Blu-ray it's presented in 16:9 and 1920x1080 throughout, it's just masked to suit.
They won't ever squash or stretch video though, so this means the original uploader stretched the 4:3 content to 16:9 at some point before upload