The VideoLAN Forums

When VLC plays back a multichannel PCM file, does it attempt to send multichannel output to iOS, or does it downmix to stereo internally before handing off the to the audiocore APIs?

Right now, we down-mix everything to a 2.0 layout, which is output as PCM (Float 32) to the AudioUnit APIs. For a future release, we will support SPDIF passthrough as the APIs we need for that were made available for iOS 8. We just didn't come around to port the respective Mac code yet.

But even SPDIF is still only 2.0 for PCM, right? As I understand it, SPDIF is only multichannel for compressed formats such as AC3 and DTS.

Yes, that's correct. SPDIF is a simple passthrough for AC3 and DTS.

Are you aware of an iOS compatible multi-channel output device which we can use to develop PCM multi-channel support?

Assuming that iOS has true USB Audio Class 2.0 support, you could potentially use something like this: https://sewelldirect.com/Soundbox-Pro-USB-Sound-Card

I've got one on order to test out right now, hence my questions.

There's more than a handful of devices that support multichannel input on iOS, using the camera connector kit. But I can't seem to find similar info for multichannel output.

http://en.ntrack.com/pro-audio-on-ipad.php

EDIT: RME also claim that their device supports iOS: http://www.rme-audio.de/en/products/fireface_ucx.php
"Playback will use analog outputs 1 and 2, or even more channels if the app supports such operation. The UCX can optionally copy the iPad playback channels 1/2 to outputs 7/8 and SPDIF/ADAT, for easier monitoring. All outputs can be processed independently (volume, EQ, dynamics, FX return)."

Nice, thanks a lot! We got the USB plug already so only the audio device itself is missing