Hi there!

I'm currently working as a multimedia designer and I do all these (except for programming).

What you would want to go for is a course in multimedia design. Usually this type of course will touch briefly on all mentioned : Graphic design, game art and development, app/ web design / programming, audio video, and animation.

You can learn this via cert / diploma /degree course (MMU/ Saito for example)or if you want a much shorter way, short courses (learning centers or online courses like Udemy / Sifoo Art / Youtube) are good enough to get you familiarize with all these field. But keep in mind that it all depends on how much time you are willing to spend on each subject to master it.