What you are looking for is called a "difference key". It supposedly determines what is different from the background and keys it over. I don't believe Vegas has this. Hitfilm might, After Effects calls it a difference matte.

That would work well, but for lazy people it can be a fair bit of work with a moving person. There is a technique where the background can be extracted via the difference between background (without human) and background with human in forground. I used to have a YT video bookmarked that talked about, but it was quite complex. The beauty of it was that it required no manual masking, although not sure how effective it was

'difference key' - thanks, that does sound familiar. I was searching for 'green screen effect without having greenscreen' and wasn't getting anything of interest, but i'll try again

I did a search and there are a lot of hits for difference key matte.

There is no way to easy achieve this in Vegas Pro, difference keying would not help for such a scene. The technology used in the video above is totally different. It recognizes faces and bodies of human beings and then removes everything else.

It works the same way as phones create fake depth of field, and that's AI based but I was reminded of differential keying, and as long as you have a clean plate of the background, and the background does not change at all, not even lighting I thought it should work. I will give the ignite Pro differential key plugin a go that Mohammed_Anis discovered. I am happy there is a plugin as from memory doing it manually using vegas is a little complex

If the subject moves very little as in you sample video, manual masking with the bezier tool will be your best free method as @Musicvid mentions. If you aren't getting paid to produce this, it may or may not be worth the effort though depending on the quality you need along the edges as you'll still have plenty of keyframes you'll need to tweak.

For Twitch Streamers there's often a need to separate them from their background for some sort of visual reaction or effect usually for comedic purposes, so within that purview the viewer is more accepting of something not looking entirely realistic/professional. I have rotoscope ptsd. I can not see the ignite pro 4 plugins, will try to reinstall. This is a clip from the default tutorial you see when searing for differential key and vegas pro. That looks ok.

@Former user

https://www.vegascreativesoftware.info/us/forum/how-to-remove-just-the-background-from-a-video--108599/#ca669265

@Former user The thing is, Color Difference key is a lesser version of Chroma. Well, not exactly, but its primary use is chroma.

I'm just giving folks here the benefit of the doubt, but I'm sincerely doubtful of its application for what you want.

Difference keying and color difference keying are two pairs of shoes. Simply spoken, difference keying is based on pulling the matte by the difference of two pixel values while color difference keying is based on pulling the matte on substracting two color channels.
Color difference keyers can be very powerful and superior to chroma keyer, e.g. Ultimatte is based on color difference keying.

In the example mentioned in the initial post a color difference keyer could not be used as there is no color background.

Ignite Pro offers both, a color difference keyer as regular FX (though Ignite's chroma keyer is better in most cases) and a difference keying as compositing mode. Compared to Vegas Pro's own difference keying the one from Ignite adds a threshold adjustment and blurring and softening of the mask.