youtube – How can I add a new audio track with uploaded sounds or music?

It seems as if YouTube Studio is still in alpha. There is no obvious way to upload your own sounds or music to use as a track, and you’re stuck with their own canned sounds.

There’s even a link to an “audio library” which allows you to only to download mp3 files from the library of sound effects, but no apparent way to actually upload them (or your own audio files) to the video editor.

Is it possible to upload your own audio files, or is Google still figuring out video editing basics while we’re all waiting impatiently?