openwith VS mpv.el

Just kidding. Of course you can open files with a key binding. I personally use a hacked version of openwith package. I wanted exactly same thing as you, to be able to open a file in external application with a key shortcut, so I have hacked original openwith.el to achieve this. My setup is like this: I press S- to open a file in external application. If I press just it will open a file in Emacs itself. So S- on a pdf file opens it in Okular in gnu/linux and just opens a pdf in Emacs with pdf-tools. You can see my setup on github if you are interested. Scroll down to * Pacakges/Dired.

I wanted libmpv in Emacs, but it ain't happening. Emacs does not have built-in music player. I think it can play ogg files, but I am not sure. I personally use mpv, but I guess vlc is fine. You could probably use moc or mpg123 if you prefer something even lighter. But mpv plays anything and works in both Windows and gnu/linux so I prefer to use it. You can also send it directories or single files, so you can just & in a filename in Dired. Otherwise EMMS is what everyone uses. I think there is also a simpler frontend to mpv but I have no idea how good it is, I have never used it, I just remember when author announced it here in this reddit.