Advanced example: sounddevice streaming

[bmcfee]

Is your feature request related to a problem? Please describe.

We somewhat often get questions about how to use librosa for stream-based processing of a live audio capture. The "PCEN Streaming" example gets us part of the way there, but it uses soundfile's block streaming mode and not a live device.

Describe the solution you'd like
We could add an example using the sounddevice package to do a frame- or block-based processing example with callbacks or asyncio.

The main challenge in setting this up would be getting the documentation to build consistently offline. I wonder if there's a way that we could mock this in the documentation build to simulate having a live device?

As a stretch goal, it would be great if the example could generate an animated display.

[bmcfee]

https://sphinx-gallery.github.io/stable/auto_examples/plot_8_animations.html#sphx-glr-auto-examples-plot-8-animations-py shows how to do animations in general.

[bmcfee]

spatialaudio/python-sounddevice#431 has some ideas for how to arrange a virtual device via jack

[bmcfee]

Looking back upon this today, it seems that the sounddevice folks have examples for stream-processing from ffmpeg output, which I think should do the trick nicely for us.

https://python-sounddevice.readthedocs.io/en/0.4.6/examples.html#play-a-web-stream