Implement Camera module for webcam access on all platforms (currently only for iOS and macOS)

[Ansraer]

Godot version:
Any version

OS/device including version:
Anything other than ios/osx

Issue description:
Godot's Camera Server and module only have support for ios and OSX. This means that trying to interact with a webcam on other platforms always fails.

There have been efforts to add support for other platforms, but none of these attempts have ever been successful.
The most promising one (#44498) attempts to add support for Windows using Media Foundation but is currently only compatible with msvc.

Steps to reproduce:
Try to use the camera server on any non apple platform

Minimal reproduction project:
https://github.com/BastiaanOlij/godot3_test_projects/tree/master/TestCameraServer

UPDATE:
There are a couple of different open PRs.
Windows: #49763 (3.x only, but should be easily portable to master)
Linux: #47967 and #53666

[Calinou]

Related to #13139 (another feature that needs to be implemented on non-Apple platforms).

[BastiaanOlij]

Note that it does also work with ARCore though that work never ended up getting merged and is now moving to a plugin.
There were attempts at implementing native Android support, can't remember what that got stuck on.

There have also been a few projects attempting to implement webcam support on Linux but getting stuck on less then stellar support for various cameras

The problem is that some of the more complete cross platform camera libraries are all behemoths unsuitable to be included in Godot (like OpenCV)

[Ansraer]

The problem is that some of the more complete cross platform camera libraries are all behemoths unsuitable to be included in Godot (like OpenCV)

Its even worse than than that. While there are smaller libraries all they did was to write a wrapper around ffmpeg or opencv and hide that fact in a footnote of the readme.
In addition, both ffmpeg and opencv use various deprecated native libraries (e.g. directshow) and, to add insult to injury, their buildsystem is a horrible outdated mess that is NOT cross platform.
After spending a few days trying to write a PR to add more platform support I came to the conclusion that the best solution will be to manually add support for each platform using native apis.
At the point of writing that would be v4l2 for linux (which appears to be actually useable!), media foundation for windows (this one is more problematic. MS uses various Macros and shortcuts that cause most compilers to dislike compiling it. I managed to get it working by manually redefining some of the macros and ignoring certain warnings, but it wasnt pretty.) and ndk for android (also looks useable).

[Schmetzler]

What is with the HTML5 support. How would one go about that? There seems to be a pretty easy way to use webcams with JavaScript... But I don't have an idea how to use this with godot?

[Calinou]

What is with the HTML5 support. How would one go about that? There seems to be a pretty easy way to use webcams with JavaScript... But I don't have an idea how to use this with godot?

Like with many advanced HTML5 features, enabling webcam access requires permission from the user. Exposing webcam support to Godot would also require handling the permission request, converting the data so it can be read from Godot, etc. It's a lot of work.