What's new in v0.9.0-beta.4

One change: USB-C headphones and dongles now work.

USB-C audio output

Plug USB-C headphones or a USB-C to 3.5mm dongle into the top port, the one
labelled OTG, and audio moves to them automatically. Unplug and it comes back to
the speaker on its own. A new USB-C entry appears in Settings > Display &
Sound while something is attached, so you can also switch by hand.

Volume is remembered per output, the same way the 3.5mm jack and Bluetooth
already were. Set headphones to one level and the speaker to another, and each
comes back where you left it.

This never worked before, in Leaf or in stock firmware. Nothing was wrong with
the hardware: the handheld already switched the port to host mode on its own and
recognised the headphones as an audio device. Leaf simply never told the audio
system the device had appeared, so nothing could see it, including RetroArch's
own audio device list.

Charging still works while headphones are in. The bottom port, labelled DC,
handles power and is separate from the OTG port, so you can do both at once.

The volume jump you may not have noticed

While fixing the above we found an older bug. After the output changed on its own
— plugging in headphones, a Bluetooth headset connecting — the first press of a
volume button jumped to a different level instead of stepping up or down by one.

That affected the 3.5mm jack and Bluetooth too, not just the new USB-C path,
and it is fixed for all three.

Testing notes

USB-C audio has been tested with exactly one set of headphones on one handheld,
so this is the part that needs other people trying it.

Worth reporting either way:

• Which USB-C device you tried, and whether it worked. Headphones with a
  built-in DAC and plain USB-C to 3.5mm dongles take the same path, but only
  headphones have actually been tried.
• Plug and unplug while a game is running, not just at the menu. Audio should
  follow immediately and come back to the speaker on unplug, with no restart.
• Volume behaviour across a switch. Set different levels on speaker and
  headphones, then swap a few times.
• The 3.5mm jack and Bluetooth, since the volume fix touches those as well.
  Nothing there should have changed except the jump.

Two things that are expected, not faults:

• A USB-C device in the OTG port disconnects USB ADB. The port has to switch
  to host mode to talk to the headphones, which shuts down the connection your
  computer was using. Wi-Fi ADB is unaffected.
• Anything already playing keeps its volume for a moment on the first switch
  to USB-C, until that output has a saved level of its own. Set it once and it
  sticks.

Everything from beta.1 through beta.3 still applies.