[Hooner]

XBMC for iOS does not appear to allow digital audio passthrough over HDMI.

I have an iPad 3 connected via HDMI to a Onkyo 5.1 digital audio receiver with the official Apple digital AV/HDMI adapter. With audio set to "HDMI" and speaker configuration on "5.1", I still get only 2-channel PCM audio. In fact, no matter what audio output setting (and why is there a selection for optical/coax?) or speaker configuration, the results are the same. The setting for "audio output device" cannot be changed, but remains locked on "default."
I have tested this with both XBMC v12 Frodo for iOS and the xbmc-20130202-3e048f8-master-ios.deb nightly build.

Digital audio passthrough to allow for full 5.1 surround sound is possible since Apple's own default Videos.app allows for playback of full 5.1 digital audio over the HDMI adapter. This seems to be real missed opportunity since I can envision people increasingly using their older iPads as part of their home theater system with XBMC.

[Ned Scott]

It's probably something not well documented, since most iOS developers aren't making their own player instead of using Apple's. In the past Apple has only listed iOS devices with the HDMI adapter as supporting stereo output, so it's also possible that this is only a feature in the last generation or two of iOS devices, and our iOS devs might not have one of those (not sure?). XBMC for iOS also has some pretty significant audio issues lingering from the new AudioEngine (wiki) in XBMC, and I suspect that will also complicate things.

It is awesome to hear that it is at least theoretically possible with the hardware, though.

[Memphiz]

Well i tried this once with my ipad1 (ios 4.3 - long time ago) - i needed to make the options for passthrough visible of course. But all i got was static noise from my amp. Basically there is no accessible way in the apple api to force 16bit output - so it uses some float conversion i guess which destroys the pass through. The fact that apple got it working in their own stuff does not mean that other developers are able to benefit from it without using apples core player components (and we don't use those because they are way to restricted for what we need in xbmc).

Though i would be able to provide you with a testbuild which has the pass through options enabled if i get some spare time (really busy atm).

[Hooner]

Thank you for your replies. I'm surprised to hear that not more people are interested in using their iPad as a home theater computer.

I'd be happy to try out a testbuild with playthrough enabled. Whenever you have time is fine with me. It would be a great feature to have in iOS XBMC.

[Memphiz]

You can also try to edit /var/mobile/Library/Preferences/XBMC/userdata/guisettings.xml and change/add

Code:

<audiooutput>
  <ac3passthrough>true</ac3passthrough>
  <dtspassthrough>true</dtspassthrough>
</audiooutput>

[Hooner]

Thanks for your suggestion. I tested this, but get only static. What about changing the parameter for passthroughdevice?

Code:

<audiooutput>
        <ac3passthrough>true</ac3passthrough>
        <audiodevice>IOSCoreAudio:default</audiodevice>
        <channels>8</channels>
        <dtspassthrough>true</dtspassthrough>
        <guisoundmode>1</guisoundmode>
        <mode>2</mode>
        <normalizelevels>true</normalizelevels>
        <passthroughdevice>default</passthroughdevice>
        <stereoupmix>false</stereoupmix>
</audiooutput>

[Memphiz]

There is only one audiodevice on ios. So basically you experienced the same as i did. Well not much i can do about it (on ATV2 we normally fixed this by setting it up to output 16bit audio - this is a setting of ios on atv2 - sadly this option is missing on all other ios devices).

Bummer...

[doclip]

I am interested to see about any new discoveries on this matter.
Any success on passthrough of AC3/DTS to receiver?

[Memphiz]

There was a user somewhere who said it works for him. But no other discoveries made. It might just be a thing of the right receiver which would support non 16bit audio (float).