USB audio output support allows hardware vendors to build hardware such as audio docks that interface with Android devices. This functionality is also exposed with the Android Open Accessory Development Kit (ADK) to give all developers the chance to create their own hardware.
So far there's no indication that they are using a standard for digital output...it could be its own standard with API calls through Android Open Accessory Development Kit
But nonetheless..this is great news.
EDIT: Just looked up the ADK website http://developer.android.com/tools/adk/adk2.html
To play audio over USB, you must use a device running Android 4.1 (API Level 16) or higher:
Plug the AC power adapter into the ADK.
Connect the Micro USB AB connector (small, rectangular plug) to the Phone port on the ADK board.
Unlock your Android device and connect the Micro USB B connector to your device. Note: Your device must support Android USB accessory mode. Devices that support this mode include Google Nexus devices.
On the Android device, you should see a prompt to connect to the ADK DemoKit 2012, select Cancel and allow the ADK to connect as a media device only.
Navigate to an application that plays music or other audio.
Play a song or sound and listen to it on the ADK speaker!
Note: When using the ADK with a USB connection to an Android device, make sure the AC power adapter is plugged in. A USB connection to a computer does not provide sufficient voltage to power both the ADK and a USB connection to a device.
Seems to be a pretty standard USB audio thing, but seems maybe the DAC or device needs some capability to send a usb control request to get the phone to start sending data to the dac??
Seems like maybe existing stuffs might work if you had a hacked rom to toggle this accessory mode manually? If we were really lucky this USB Control request that is needed to start the streaming mode is more standard than it seems?? Regardless it really seems were are just a minor USB DAC chip tweak away from android phone USB Audio goodness at worse.
Confirmed that fiio e7 does not work with the new android 4.1 os on a galaxy nexus toro. I just tried it and have played around with it for a while trying to get it to work. This is a huge let down for me. Looks like I might be spending the money on that galaxy S3 after all.
Yeah, I think we will need the source released to get this working on legacy DACs maybe. Toro could have issues just because we need 4.1 proprietary files though. GSM might already work if some of this is proprietary file related as I figure its update hit some of those. It may take DAC updates without hacked AOSP built Roms also. Seems we are closer than ever though.