SDL2 - Add video recording support

[glisignoli]

Like the windows version. It would be good to have some sort of video file output

[dinkc64]

This is a good idea, but only if it can be pulled off in a way which doesn't require importing something huge like ffmpeg into our project.

[glisignoli]

I've been looking for other examples where a SDL2 output is rendered to a file. The only examples I can find is using SDL_SaveBMP.

https://github.com/xmoto/xmoto has some method of recording to files, so that might be a good starting point.

https://github.com/xmoto/xmoto/blob/f0da37df08e71ccba4d796e81749f5e0a4da34a3/src/xmoto/VideoRecorder.cpp

Even if the audio and video streams were saved to separate files then something could be used to merge them afterwards (provided they sync correctly)

[barbudreadmon]

@glisignoli i'll mention it : i don't think @tmaul (who wrote this sdl2 port) will have free time to work on this anytime soon, so external PRs are very welcome if you want new features implemented in this port.

Otherwise, the reason why i recommended the libretro port for linux when you asked on discord was because it has all kind of features, including this one.