I would like to change the shutter speed by starting the camera on the terminal with javascript.

It seems that this article and the link from it deal with a similar topic, but it may be possible to do so with an experimental API that only works with Chrome.
getUserMedia lock focus/expose

What I would like to do, once the page starts taking snapshots, lock the getUserMedia camera's focus/exposure, so that in between snapshot intervals the environment can change without the light balance changing or the camera refocusing.
What I want to do is lock the focus/exposure of the getUserMedia camera when the page starts taking snapshots so that the environment can be changed during the snapshot interval without changing the light balance or refocusing the camera.

Not yet.Unfortunately, WebRTC does not allow photo-level access to cameraas, but a new Image Capture spec is being worked on to solve this. None of the browsers implementation it through.> Still. Unfortunately, WebRTC does not allow photo-level access to the camera, but we are working on a new ImageCapture specification to resolve this. However, none of the browsers have been implemented yet.

Take photo when the camera is automatically focused
Why the difference in native camera resolution-vs-getUserMedia on iPad/iOS?

If you read the article around here, it seems that you can manipulate the shutter speed indirectly by manipulating information related to exposure and iso.

Shutter speed - Wikipedia /Shutter speed-Wikipedia

Shutter speed refers to the time when the shutter is opened and the film or imaging device is exposed (exposed) to light through the lens (also abbreviated as exposure time, shutter speed, SS) when taking a picture with a camera.

CAMERA EXPOSURE

MediaStream Image Capture

W3C Working Draft, 6 April 2021 9.4.MediaTrackSettingsdictionary
DOMSstring exposureMode;
double exposureCompensation;
double exposureTime;
doubleiso;

MediaStream Image Capture API

Experimental This is an experimental function.
Check your browser compatibility chart before using it in production.

Use your camera on the web – WebRTC (getUserMedia) on WebView

Fine controls
For your information, I will list the results of each browser.
Google Chrome

"exposureCompensation": true,
"exposeMode": true,
"exposeTime": true,
"iso": true,

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